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National Boards => General Highway Talk => Topic started by: tradephoric on May 18, 2015, 02:51:37 PM

Title: Crash prone 'modern roundabouts'
Post by: tradephoric on May 18, 2015, 02:51:37 PM
In 2013, a modern roundabout was constructed at the intersection of Ellsworth & State in Ann Arbor, Michigan.  Three years prior to the roundabout construction, the intersection averaged 16 crashes per year.  The first year after the roundabout was completed, Ellsworth & State experienced the highest number of accidents in the entire state of Michigan (168 total crashes). 

Ann Arbor roundabout has most crashes in Michigan
http://www.mlive.com/news/ann-arbor/index.ssf/2015/03/roundabout_on_ann_arbors_south.html
http://www.semcog.org/Data-and-Maps/Crash-and-Road-Data/Point_Id/81016689/view/RoadIntersectionCrashDetail

Are there other crash prone modern roundabouts that you are aware of? 
Title: Re: Crash prone 'modern roundabouts'
Post by: froggie on May 18, 2015, 03:57:00 PM
Speaks more to the (in)flexibility of Michigan drivers than it does any inherent safety risk with roundabouts.  New roundabouts elsewhere have seen major drops in the number of crashes.
Title: Re: Crash prone 'modern roundabouts'
Post by: NE2 on May 18, 2015, 04:20:09 PM
PARCLO B4
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on May 18, 2015, 04:26:03 PM
Here it is: https://goo.gl/maps/NGJmj .  Is that a 'standard' roundabout?  You almost drive straight out of the roundabout, rather than curve out.  Plus that right turn only bypass comes out very close to the actual roundabout. 

I think there's a legit design issue here.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on May 18, 2015, 06:27:21 PM
Speaks more to the (in)flexibility of Michigan drivers than it does any inherent safety risk with roundabouts.  New roundabouts elsewhere have seen major drops in the number of crashes.

The safety statistics most often cited to the public are based on a 2000 study done by the Insurance Institute for Highway Safety.  A few points should be considered.  Of the 24 roundabouts analyzed, only 3 were previously signalized intersections (21 intersections were non-signalized).  Also, no roundabout had an AADT of greater than 31,000 vehicles.  The study observed that modern roundabouts have the following safety benefits:
•   38% reduction in total crashes
•   76% reduction in injury crashes
•   90% reduction in fatal and incapacitating-injury crashes

In 2011, the Wisconsin Department of Transportation funded a study that analyzed 24 roundabouts in their state.  In the Wisconsin study, a roundabout with an AADT of 70,000 was analyzed (over twice the traffic volumes of any roundabout included in the 2000 study).  Of the 24 roundabouts analyzed, 11 saw crashes increase after the roundabout was completed and 6 saw crashes increase by over 40%.   Overall, they observed the following safety benefits:
•   9% reduction in total crashes
•   52% reduction in injury crashes

Here is a summary of the roundabouts analyzed in the Wisconsin study:
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Wisconsin_zpsgjcbnfpd.png)


Title: Re: Crash prone 'modern roundabouts'
Post by: Big John on May 18, 2015, 06:36:15 PM
^^ #7 STH 141?
WisDOT should know better than that. :pan:
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on May 18, 2015, 09:42:33 PM
^^ #7 STH 141?
WisDOT should know better than that. :pan:

Does traffic back up through the roundabout when a train goes by?

https://www.google.com/maps/@44.4588082,-87.950588,141m/data=!3m1!1e3
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on May 19, 2015, 02:38:26 AM
First year stats are such horse shit. Driver familiarity is a major preventer of collisions at intersections (drivers know what to expect; driver behavior, what each lane does, signal phases, etc). Changing literally anything will throw people off and you're probably gonna have a few additional collisions. I'll admit, that's a big jump, but I guarantee you tradephoric, the collisions will fall. Let's revisit this intersection in a couple years.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on May 19, 2015, 10:44:09 AM
First year stats are such horse shit. Driver familiarity is a major preventer of collisions at intersections (drivers know what to expect; driver behavior, what each lane does, signal phases, etc). Changing literally anything will throw people off and you're probably gonna have a few additional collisions. I'll admit, that's a big jump, but I guarantee you tradephoric, the collisions will fall. Let's revisit this intersection in a couple years.

Seeing a spike in crashes at SE Michigan roundabouts is not uncommon.  I touched on this in a previous thread.

The chart below looks at crash data of 16 major roundabouts built throughout SE Michigan between 2006-2009.  While PDO accidents spike the first year after roundabout construction, injury accidents drop from day one.  By year two people seem to get use to them and the PDO steadily declines from the initial spike.  This has at least been the trend for SE Michigan.
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/RBuntitled_zps758a2437.png)

If the crashes at Ellsworth & State jumped from 16 to 32, that would be par for the course.  However, it jumped from 16 to 168 crashes.  There’s a problem here.  To put this in perspective, the intersection with the 2nd most crashes in Michigan for 2014 had 87 crashes (12 Mile & Orchard Lake). 
Title: Re: Crash prone 'modern roundabouts'
Post by: Bickendan on May 19, 2015, 01:08:08 PM
Having glanced at the roundabout in question in Streetview, I don't see anything inherently wrong with the design. My gut says it's driver inflexibility and impatience, which will eventually largely evaporate as drivers get familiar with the design.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on May 19, 2015, 02:05:13 PM
Here are a list of roundabouts where total crashes have doubled since the completion of the roundabout (when averaging the 3 years before to 3 years after crash data).   To view the most up to date aerials you may have to input the coordinates into GE.  Do these roundabouts share any attributes that could explain the increase in crashes? 

(950%) Ellsworth Rd & State Rd (Ann Arbor, Michigan):
https://www.google.com/maps/@42.22941,-83.73873,17z/data=!3m1!1e3?dg=brw

(335%) Livernois Rd & Hamlin Rd (Rochester Hills, Michigan):
https://www.google.com/maps/@42.6518911,-83.1526542,137m/data=!3m1!1e3

(297%) Canal & 25th Street (Milwaulkee, Wicsonsin):
https://www.google.com/maps/@43.0311071,-87.9434376,92m/data=!3m1!1e3

(266%) SB US23 & Lee Road (Brighton, Michigan):
https://www.google.com/maps/@42.5059638,-83.759329,117m/data=!3m1!1e3

(135%) Cass Ave & Romeo Plank (Clinton, Michigan):
https://www.google.com/maps/@42.6113704,-82.9322543,117m/data=!3m1!1e3

(127%) STH 32/STH57 & Broadway (De Pere, Wisconsin):
https://www.google.com/maps/@44.4474383,-88.0602622,117m/data=!3m1!1e3
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on May 19, 2015, 02:06:38 PM
Having glanced at the roundabout in question in Streetview, I don't see anything inherently wrong with the design. My gut says it's driver inflexibility and impatience, which will eventually largely evaporate as drivers get familiar with the design.

But 3 years?   Usually familiarity takes a week for most drivers; maybe a month for more infrequent drivers.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on May 19, 2015, 02:27:06 PM
To jeffandnicole's point, in these studies no crash data is analyzed from the year the roundabout was constructed.  If a roundabout was completed in October, drivers have at least a few months to get use to before any crashes are included in the analysis.

For anyone interested, here's a link to the Wisconsin study:
http://www.topslab.wisc.edu/programs/safety/projects/roundabouts/WI%20Roundabout%20Evaluation%20Volume%202%20Safety.pdf


Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on May 19, 2015, 03:51:46 PM
For anyone interested, here's a link to the Wisconsin study:
http://www.topslab.wisc.edu/programs/safety/projects/roundabouts/WI%20Roundabout%20Evaluation%20Volume%202%20Safety.pdf

I'm sure it's in there, but I can't find it. Any idea what the common collisions were? (Like sideswipes, T-bone, etc).

Even if collisions are higher with roundabouts, I'm tempted to say that's preferable to, say, *consistent* fatal collisions. Have these roundabouts had fatal collisions? And were they contributed to driver error or a design fault? I ask that, because, roundabouts should work well -- their design is not the inherent cause of these collisions.
Title: Crash prone 'modern roundabouts'
Post by: 6a on May 19, 2015, 04:16:01 PM
Angle and sideswipe both had gigantic increases (at the Ann Arbor intersection). Like, those two accounted for almost all of the increase. I wonder if jeffandnicole is on to something regarding that right turn bypass bit. Looking at the crash increases it really does make me wonder if it's just people not staying in the correct lane. I'm not terribly familiar with the area - is this intersection near the university?

Closer to home here, I'm really curious to see what happens to this one, currently under construction:

(http://images.tapatalk-cdn.com/15/05/19/1bb12405f7a9e8b0cf49d995ebc3400d.jpg)

Traffic count sits at 50,000 currently, and even with left turns banned on the E-W route (SR 161) it's the third worst intersection for crashes in the city of Dublin. I believe it will be the first in the area to have a three lane section, but Dublin is the king of roundabouts locally, so like I said, I'm really curious to see the results.

Edit: oh wow, on that Ann Arbor one, you can see right across it. Could that be a cause for distraction?

(http://images.tapatalk-cdn.com/15/05/19/6e56d11a07db1e448e4e6bbf467d84b0.jpg)
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on May 19, 2015, 04:30:23 PM
Edit: oh wow, on that Ann Arbor one, you can see right across it. Could that be a cause for distraction?

That's a very good point. One of the reasons the Carmel, Indiana roundabouts are so successful is because of their decoration.
Title: Re: Crash prone 'modern roundabouts'
Post by: johndoe on May 19, 2015, 07:40:29 PM
Cool thread, good info.  I wonder if this roundabout has tangents on entry and what the fastest path speeds are. 
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on May 19, 2015, 10:11:22 PM
For anyone interested, here's a link to the Wisconsin study:
http://www.topslab.wisc.edu/programs/safety/projects/roundabouts/WI%20Roundabout%20Evaluation%20Volume%202%20Safety.pdf

I'm sure it's in there, but I can't find it. Any idea what the common collisions were? (Like sideswipes, T-bone, etc).

Even if collisions are higher with roundabouts, I'm tempted to say that's preferable to, say, *consistent* fatal collisions. Have these roundabouts had fatal collisions? And were they contributed to driver error or a design fault?  I ask that, because, roundabouts should work well -- their design is not the inherent cause of these collisions.
 

Check out Table 4 on page 20.  There was big increases in sideswipe-same direction (SSS) crashes in the Wisconsin study (increasing from 10 in the before condition to 75 in the after).   



Title: Re: Crash prone 'modern roundabouts'
Post by: Brian556 on May 19, 2015, 10:35:24 PM
I said it before, I do not like multi-lane roundabouts. They are just too complicated, and can confuse drivers.  Only single-lane roundabouts should be allowed. Even single lane roundabouts can have issues, especially if drivers enter them too fast. Also, if there is too high of a volume of traffic entering from one direction, the other directions can have a hard time even getting a chance to enter the roundabout. The ones in Windermere, FL have this problem, particularly the southern one.
https://www.google.com/maps/place/Windermere,+FL/@28.4949864,-81.5342674,398m/data=!3m1!1e3!4m2!3m1!1s0x88e7635aece2fef1:0xfac6dfbac566065e (https://www.google.com/maps/place/Windermere,+FL/@28.4949864,-81.5342674,398m/data=!3m1!1e3!4m2!3m1!1s0x88e7635aece2fef1:0xfac6dfbac566065e)

There is a new one in Flower Mound, TX that I don't care for due to the rather high traffic volume. To me it's a pain in the ass having to deal with the high traffic volume, and trying to figure out when it is safe to enter the roundabout, especially from a stopped position. I'd personally rather have a signal at this particular location:
https://www.google.com/maps/@33.0664592,-97.0879309,95m/data=!3m1!1e3 (https://www.google.com/maps/@33.0664592,-97.0879309,95m/data=!3m1!1e3)
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on May 19, 2015, 11:53:34 PM
I do not like multi-lane roundabouts. They are just too complicated, and can confuse drivers.

That is a gross over-generalization. There are plenty of multi-lane roundabouts (near me) that have zero issues.

In your defence, however, there are certainly areas in this country where the "courtesy" behaviour (necessary for a successful roundabout) doesn't exist. Texas springs to mind, along with much of the south and perhaps Midwest. Places like rural New England, the Pacific Northwest, and perhaps pockets of the Southwest are the best candidates for roundabouts, since they have the most courteous (and thus the most observant) drivers (at least in my experience).
Title: Re: Crash prone 'modern roundabouts'
Post by: renegade on May 20, 2015, 01:36:15 AM
Re:  State and Ellsworth in Ann Arbor:  It's a well-thought-out roundabout  Part of the problem is, northbound on State, there's a traffic signal which favors the side road about 150 yards north of the roundabout.  All the traffic-flow in the world is rendered useless if there's no place for it to go.  The other problem is that no one wants to learn to maneuver properly.  Some enter the roundabout without yielding to traffic already within, while others will gladly stop in the middle to let others in.  Hell, I personally witnessed on driver who said, "Fuck this" and turned left instead of going around.

Title: Re: Crash prone 'modern roundabouts'
Post by: KEK Inc. on May 20, 2015, 02:45:08 AM
I do not like multi-lane roundabouts. They are just too complicated, and can confuse drivers.

That is a gross over-generalization. There are plenty of multi-lane roundabouts (near me) that have zero issues.

In your defence, however, there are certainly areas in this country where the "courtesy" behaviour (necessary for a successful roundabout) doesn't exist. Texas springs to mind, along with much of the south and perhaps Midwest. Places like rural New England, the Pacific Northwest, and perhaps pockets of the Southwest are the best candidates for roundabouts, since they have the most courteous (and thus the most observant) drivers (at least in my experience).

I've run into dangerous congestion at these roundabouts when I went kayaking in Olympia last.

https://www.google.com/maps/place/Olympia,+WA/@47.0449015,-122.9119405,18z/data=!4m2!3m1!1s0x5491c9c1ae285569:0x4f146197e2881b83
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on May 20, 2015, 03:25:47 AM
I do not like multi-lane roundabouts. They are just too complicated, and can confuse drivers.

That is a gross over-generalization. There are plenty of multi-lane roundabouts (near me) that have zero issues.

In your defence, however, there are certainly areas in this country where the "courtesy" behaviour (necessary for a successful roundabout) doesn't exist. Texas springs to mind, along with much of the south and perhaps Midwest. Places like rural New England, the Pacific Northwest, and perhaps pockets of the Southwest are the best candidates for roundabouts, since they have the most courteous (and thus the most observant) drivers (at least in my experience).

I've run into dangerous congestion at these roundabouts when I went kayaking in Olympia last.

https://www.google.com/maps/place/Olympia,+WA/@47.0449015,-122.9119405,18z/data=!4m2!3m1!1s0x5491c9c1ae285569:0x4f146197e2881b83

I've gone through those a couple of times. Never had any issues, but the odd manner in which they facilitate through traffic would more than likely exacerbate traffic flow.

Any idea if Olympia publishes any stats on these roundabouts? The only documents I can find on the so-called "Gateway Project" (as it was called in 2003 -- how original) only seem to be promoting it, if you know what I mean.
Title: Re: Crash prone 'modern roundabouts'
Post by: KEK Inc. on May 20, 2015, 03:26:57 AM
I think they're a bit too close to each other.  I also went during rush hour.
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on May 20, 2015, 03:38:09 AM
I think they're a bit too close to each other.  I also went during rush hour.

I'd rather have two closely spaced roundabouts than two closely spaced signals. Then again, they don't seem that close?
Title: Re: Crash prone 'modern roundabouts'
Post by: cpzilliacus on May 20, 2015, 03:34:14 PM
A roundabout in the municipality of Mount Rainier, Prince George's County, Maryland on U.S. 1 (Rhode Island Avenue) just north of the District of Columbia border at 34th Street. 

This roundabout (https://www.google.com/maps/place/Mt+Rainier,+MD/@38.936294,-76.960984,3a,26.4y,47.29h,81.51t/data=!3m4!1e1!3m2!1s469xw_VJTQOCuZtYSmrG7A!2e0!4m2!3m1!1s0x89b7c7a0d961e31f:0x38df1d15661676d1!6m1!1e1) features a rather massive concrete "planter" inside, which gets crashed into somewhat often by drunk/impaired drivers headed out of D.C.

I don't think it is poorly designed, and it improves Maryland traffic safety by "intercepting" some of those impaired motorists before they crash into something else, or a pedestrian or bicyclist.
Title: Re: Crash prone 'modern roundabouts'
Post by: Brian556 on May 20, 2015, 03:46:12 PM
Quote from cpzilliacus:
Quote
I don't think it is poorly designed, and it improves Maryland traffic safety by "intercepting" some of those impaired motorists before they crash into something else, or a pedestrian or bicyclist.

Now that gives me an idea. Create "drunk driver traps" by creating "hazards" that you would have to be drunk to drive into, to protect the general public.
I'm not necessarily advocating concrete planters, but something like a runway truck ramp with mud, and sign it "mud pit". Since drunk drivers can't even read DO NOT ENTER or WRONG WAY signs, they wouldn't read the "MUD PIT" sign either, and would drive right into it.
Title: Re: Crash prone 'modern roundabouts'
Post by: 6a on May 20, 2015, 03:52:13 PM

I think they're a bit too close to each other.  I also went during rush hour.

I'd rather have two closely spaced roundabouts than two closely spaced signals. Then again, they don't seem that close?

These work just fine. A bit slow at rush hour but compared to the old signals it's a big improvement.

(http://images.tapatalk-cdn.com/15/05/20/434e6b90f4e62f7968f4416834fa3ba0.jpg)
Title: Re: Crash prone 'modern roundabouts'
Post by: froggie on May 20, 2015, 04:07:32 PM
The Wisconsin and Michigan experiences that tradephoric commented on are the general opposite of Minnesota's experience, at least anecdotally as I don't think MnDOT has done a comprehensive study yet.  They have studied a few roundabouts, including a rural roundabout in particular (on MN 13 in Scott County), built in response to multiple fatal crashes, where there were HUGE declines in overall crashes after the roundabout was completed.  There's also a study documenting a multilane roundabout in Richfield that did see a high number of crashes (there wasn't really anything to compare it to pre-construction), but after tweaking with signage and striping saw crashes and "illegal turns" (i.e. turning left from the outer lane) decrease by about half.  This Richfield study/research may hold the key to getting better results out of multilane roundabouts.

Title: Re: Crash prone 'modern roundabouts'
Post by: Sykotyk on May 20, 2015, 08:47:05 PM
I think there's two culprits: unfamiliarity of, and lack of obedience to the laws of traffic circles/roundabouts. So many drivers see the "Yield" sign as 'hurry up before the other guy gets there" rather than what it truly means, which is basically a stop sign that allows you to roll through if there's no side traffic. Not high speed. And it's not a race. And when traffic builds incredibly deep on more than one approach, the general rule of stop-signs take over and you take turns, rather than one road releasing everyone at once because tailgating through the yield and that stops everyone else from entering the traffic circle.

I've seen it in the northeast in the new smaller 'modern' ones. Funny the old ones up in Boston are handled fine. But make one about 100' diameter island in the middle, and suddenly it's a race to claim your spot in the middle.
Title: Re: Crash prone 'modern roundabouts'
Post by: roadfro on May 20, 2015, 10:15:02 PM
Here it is: https://goo.gl/maps/NGJmj .  Is that a 'standard' roundabout?  You almost drive straight out of the roundabout, rather than curve out.  Plus that right turn only bypass comes out very close to the actual roundabout. 

I think there's a legit design issue here.

I would agree with you. While it is designed to be a standard roundabout (as opposed to other traffic circles), it is lacking with some design features that can lead to issues.

The lack of deflection angles on the exits encourages circulating drivers to speed up while exiting, which I imagine contributes to collisions. In particular, the southbound exit point has no deflection at all.

The right turns also appear to be an issue. It looks like it easy to just turn right, without having to stop/yield, enter the circulatory area, then exit...instead sort of just not slowing and turning right since it looks like it's wide enough to just sneak by.

The southbound right turn bypass really just doesn't make sense. A right turn bypass lane in a roundabout only makes sense if it is free flowing. That seems like it might be a source of issues, and looks like it could be more angle accidents at that point instead of sideswipes. It also looks like that right turn would have visibly issues if there is also a car stopped in the lane adjacent to the "bypass" lane.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on May 20, 2015, 10:22:00 PM
I do not like multi-lane roundabouts. They are just too complicated, and can confuse drivers.

That is a gross over-generalization. There are plenty of multi-lane roundabouts (near me) that have zero issues.

Early findings of 5 multi-lane roundabouts in Washington State show that there has been a 56% increase in total crashes.  It’s not uncommon to see an increase in crashes at multi-lane roundabouts because drivers are exposed to a lot more sideswipe crashes.  The Washington State crash data is linked in this article below (click 'Early findings in Washington state'):

http://www.seattletimes.com/seattle-news/new-roundabout-aims-to-make-hwy-9-safer-in-growing-marysville/

Multi-lane roundabouts do a great job at reducing injury crashes but there is growing evidence that they don't reduce total crashes.  Single-lane roundabouts, OTOH, do a better job at reducing total crashes, but have less of an impact in reducing injury crashes.  This chart in the Wisconsin study illustrates these points.

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/singlevsdouble_zps1r60v17i.png)
Title: Re: Crash prone 'modern roundabouts'
Post by: Tarkus on May 20, 2015, 10:29:30 PM
As I've mentioned on other threads, Oregon's multi-lane roundabouts are absolutely terrible.  The one at US-101/OR-202 in Astoria has, over the long term, resulted in a 150% increase in crashes, without any reduction in accident severity, and even pro-roundabout traffic engineers I've talked to concur with the notion of that roundabout being terrible.  Given the wacky mess that was there before the roundabout, screwing things up that bad is quite a feat.  Of course, given that it was built by ODOT, I can't say I'm surprised, sadly.

Even worse is the one at MLK Pkwy, Pioneer Parkway, and Hayden Bridge Way in Springfield.  It cost almost $10 million to build, and it had almost 200 accidents between 2009 and 2013, with volumes only running 15,000-20,000 ADT.  The city's own transportation study showed it having an accident rate nearly 3 times that of the second-place intersection on a per MEV basis, but because it cost so much to build, they aren't rushing to fix it.

I think single-lane roundabouts do have a place--situations involving weird intersection geometry on mid-speed collectors and arterials (30-40mph range, and especially if people actually use their turn indicators)--but multi-lane roundabouts have had a very mixed record nationwide, and they're prohibitively expensive.
Title: Re: Crash prone 'modern roundabouts'
Post by: lordsutch on May 20, 2015, 10:38:23 PM
I don't think anyone ever argued that roundabouts reduce collisions overall. What they argued was that, by reducing conflict points and angle of incidence (particularly head-on and T-bone collisions), they reduce the severity of the collisions that do occur, particularly compared to all-way stop and signalized intersections.

I also think some of the first-year collision issues are the result of insufficient public education efforts, particularly in areas with few existing roundabouts. Putting in place a temporary VMS on each leg 500 yards or so upstream that says "YIELD TO CIRCULATING TRAFFIC" for the first three months or so would do wonders.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on May 20, 2015, 11:15:39 PM
I don't think anyone ever argued that roundabouts reduce collisions overall. What they argued was that, by reducing conflict points and angle of incidence (particularly head-on and T-bone collisions), they reduce the severity of the collisions that do occur, particularly compared to all-way stop and signalized intersections.

That's exactly what's being argued though.  Listen to what Jeannie Willis has to say about the expected safety benefits of a 3-lane roundabout currently under construction in Dublin, Ohio (6A touched on this roundabout previously in this thread).  What are the residents of Dublin to think if her predictions don't come to pass?  At that point, who cares right?  It will already be constructed.


Quote
“They improve safety.  We will reduce crashes.  It won’t eliminate crashes.  The frequency of the crashes will be reduced and the severity will be reduced, of the crashes, meaning the number of injury related type crashes will be substantially reduced.”

-Jeannie Willis, Engineering Manager, City of Dublin
Title: Re: Crash prone 'modern roundabouts'
Post by: Bickendan on May 21, 2015, 12:35:51 AM
I don't think anyone ever argued that roundabouts reduce collisions overall. What they argued was that, by reducing conflict points and angle of incidence (particularly head-on and T-bone collisions), they reduce the severity of the collisions that do occur, particularly compared to all-way stop and signalized intersections.

That's exactly what's being argued though.  Listen to what Jeannie Willis has to say about the expected safety benefits of a 3-lane roundabout currently under construction in Dublin, Ohio (6A touched on this roundabout previously in this thread).  What are the residents of Dublin to think if her predictions don't come to pass?  At that point, who cares right?  It will already be constructed.
Uh... is this supposed to be a disagreement to what lordsutch said?
Title: Re: Crash prone 'modern roundabouts'
Post by: lordsutch on May 21, 2015, 12:47:34 AM
That's exactly what's being argued though.  Listen to what Jeannie Willis has to say about the expected safety benefits of a 3-lane roundabout currently under construction in Dublin, Ohio (6A touched on this roundabout previously in this thread).  What are the residents of Dublin to think if her predictions don't come to pass?  At that point, who cares right?  It will already be constructed.

Well, I can't speak for the specific roundabout being built; it's entirely possible that the existing intersection is so dangerous that it will reduce both the absolute frequency and severity of crashes (the data suggest some roundabouts do lead to less crashes than the intersections they replaced, and without systematically distinguishing between what the previous intersection type was it's hard to predict which will reduce crashes and which will lead to more crashes).

Assuming this is the intersection in question (https://www.google.com/maps/place/Dublin,+OH/@40.0995925,-83.1097332,250m/data=!3m1!1e3!4m2!3m1!1s0x8838ecc4d450a11f:0xc2176815689028!6m1!1e1), given the weird angle of the existing intersection I suspect the multilane roundabout will be an improvement on both scores.
Title: Re: Crash prone 'modern roundabouts'
Post by: Bickendan on May 21, 2015, 12:56:41 AM
That looks like the intersection in question. I didn't know Tim Horton's was on this side of the 48 though.
Title: Re: Crash prone 'modern roundabouts'
Post by: KEK Inc. on May 21, 2015, 02:31:15 AM
Speaking of bypass lanes, this sort of defeated the purpose of one.

https://www.google.com/maps/place/Sammamish,+WA/@47.56748,-122.054552,3a,88.7y,306.83h,90.46t/data=!3m4!1e1!3m2!1sZJeqqwehPIZI-Jr77sbkZg!2e0!4m2!3m1!1s0x549071edd8f91263:0xcd921b1280bf0b3a!6m1!1e1

Sometimes it's faster just to go in the roundabout.

---
The big danger of multi-lane roundabouts are that drivers not familiar with the area might notice they're in the wrong lane while in the circle and decide to make an illegal maneuver that may result in a collision.  Proper signage would be better.  I think WisDOT has an overhead mast arm with information on which lane to go to for their multi-lane roundabouts. 
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on May 21, 2015, 02:46:43 AM
I do not like multi-lane roundabouts. They are just too complicated, and can confuse drivers.

That is a gross over-generalization. There are plenty of multi-lane roundabouts (near me) that have zero issues.

Early findings of 5 multi-lane roundabouts in Washington State show that there has been a 56% increase in total crashes.  It’s not uncommon to see an increase in crashes at multi-lane roundabouts because drivers are exposed to a lot more sideswipe crashes.  The Washington State crash data is linked in this article below (click 'Early findings in Washington state'):

I wish that study included newer roundabouts. They stopped gathering data at two-thirds of those intersections ten years ago. That's hardly meaningful data.

Speaking of bypass lanes, this sort of defeated the purpose of one.
...
Sometimes it's faster just to go in the roundabout.

That one has always confused me. First, trucks aren't allowed through it (perhaps they should straighten the slip lane?) and now the slip-lane merge following the roundabout has had its merge area removed. I guess too many people failed to yield.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on May 21, 2015, 07:14:56 AM
I don't think anyone ever argued that roundabouts reduce collisions overall. What they argued was that, by reducing conflict points and angle of incidence (particularly head-on and T-bone collisions), they reduce the severity of the collisions that do occur, particularly compared to all-way stop and signalized intersections.

That's exactly what's being argued though.  Listen to what Jeannie Willis has to say about the expected safety benefits of a 3-lane roundabout currently under construction in Dublin, Ohio (6A touched on this roundabout previously in this thread).  What are the residents of Dublin to think if her predictions don't come to pass?  At that point, who cares right?  It will already be constructed.
Uh... is this supposed to be a disagreement to what lordsutch said?

Uh... Yes. 

Lordsutch said "I don't think anyone ever argued that roundabouts reduce collisions overall."  Jeannie Willis, the engineering manager for the City of Dublin, argued that "the frequency of the crashes will be reduced".
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on May 21, 2015, 08:13:00 AM
I'm pretty sure any road design that's created to increase accidents is, um, how should I put it...fucked up.

I'm pretty sure the design & intent of a roundabout is to reduce congestion.  They are also supposed to reduce accidents, and when accidents occur, they are less severe.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on May 21, 2015, 01:23:11 PM
Here are a list of roundabouts where total crashes have doubled since the completion of the roundabout (when averaging the 3 years before to 3 years after crash data).   To view the most up to date aerials you may have to input the coordinates into GE.  Do these roundabouts share any attributes that could explain the increase in crashes? 

(950%) Ellsworth Rd & State Rd (Ann Arbor, Michigan):
https://www.google.com/maps/@42.22941,-83.73873,17z/data=!3m1!1e3?dg=brw

(335%) Livernois Rd & Hamlin Rd (Rochester Hills, Michigan):
https://www.google.com/maps/@42.6518911,-83.1526542,137m/data=!3m1!1e3

(297%) Canal & 25th Street (Milwaulkee, Wicsonsin):
https://www.google.com/maps/@43.0311071,-87.9434376,92m/data=!3m1!1e3

(266%) SB US23 & Lee Road (Brighton, Michigan):
https://www.google.com/maps/@42.5059638,-83.759329,117m/data=!3m1!1e3

(135%) Cass Ave & Romeo Plank (Clinton, Michigan):
https://www.google.com/maps/@42.6113704,-82.9322543,117m/data=!3m1!1e3

(127%) STH 32/STH57 & Broadway (De Pere, Wisconsin):
https://www.google.com/maps/@44.4474383,-88.0602622,117m/data=!3m1!1e3


The central island diameter for all these roundabouts is 115 feet or less.  Are the increase in crashes due to the fact that the roundabouts are just too small?  I understand the whole idea of modern roundabouts is to slow down the speed of traffic, but if they are too tight drivers seem to have more difficulty with the following tasks....

A). judging gaps in traffic to enter the roundabout (leading to angle crashes).
B). physically staying in their lane while navigating through the roundabout (leading to sideswipe same crashes).

There are plenty of multi-lane roundabouts with central island diameters of over 150 feet (with entry and exit deflection angles to keep the speed of traffic down).  Could larger multi-lane roundabouts be more effective at reducing total crashes?  I'm thinking of a roundabout like this...

https://www.google.com/maps/@45.7550012,-108.6169408,162m/data=!3m1!1e3
Title: Re: Crash prone 'modern roundabouts'
Post by: english si on May 21, 2015, 02:34:38 PM
This (https://www.google.com/maps/@51.602441,-0.631994,3a,70.4y,164.82h,69.89t/data=!3m4!1e1!3m2!1s-yrhCch_NuWYODXdEKPSiA!2e0) 10ft island diameter multi-lane roundabout doesn't see accidents. It does have traffic issues, but that is because of other factors (like not having a N-S bypass of the town, not enough space there) than because it is a roundabout.
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on May 21, 2015, 02:45:51 PM
Here are a list of roundabouts where total crashes have doubled since the completion of the roundabout (when averaging the 3 years before to 3 years after crash data).   To view the most up to date aerials you may have to input the coordinates into GE.  Do these roundabouts share any attributes that could explain the increase in crashes? 

(950%) Ellsworth Rd & State Rd (Ann Arbor, Michigan):
https://www.google.com/maps/@42.22941,-83.73873,17z/data=!3m1!1e3?dg=brw

(335%) Livernois Rd & Hamlin Rd (Rochester Hills, Michigan):
https://www.google.com/maps/@42.6518911,-83.1526542,137m/data=!3m1!1e3

(297%) Canal & 25th Street (Milwaulkee, Wicsonsin):
https://www.google.com/maps/@43.0311071,-87.9434376,92m/data=!3m1!1e3

(266%) SB US23 & Lee Road (Brighton, Michigan):
https://www.google.com/maps/@42.5059638,-83.759329,117m/data=!3m1!1e3

(135%) Cass Ave & Romeo Plank (Clinton, Michigan):
https://www.google.com/maps/@42.6113704,-82.9322543,117m/data=!3m1!1e3

(127%) STH 32/STH57 & Broadway (De Pere, Wisconsin):
https://www.google.com/maps/@44.4474383,-88.0602622,117m/data=!3m1!1e3


The central island diameter for all these roundabouts is 115 feet or less.  Are the increase in crashes due to the fact that the roundabouts are just too small?  I understand the whole idea of modern roundabouts is to slow down the speed of traffic, but if they are too tight drivers seem to have more difficulty with the following tasks....

A). judging gaps in traffic to enter the roundabout (leading to angle crashes).
B). physically staying in their lane while navigating through the roundabout (leading to sideswipe same crashes).

There are plenty of multi-lane roundabouts with central island diameters of over 150 feet (with entry and exit deflection angles to keep the speed of traffic down).  Could larger multi-lane roundabouts be more effective at reducing total crashes?  I'm thinking of a roundabout like this...

https://www.google.com/maps/@45.7550012,-108.6169408,162m/data=!3m1!1e3

Many modern roundabouts have small diameter medians; with a slightly raised inner ring apron for large vehicles.  Most don't seem to have any issues with accidents.
Title: Re: Crash prone 'modern roundabouts'
Post by: Brandon on May 21, 2015, 04:03:46 PM
That looks like the intersection in question. I didn't know Tim Horton's was on this side of the 48 though.

48?  I think you mean 49th, and yes, they are on both side of the border.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on May 21, 2015, 09:29:52 PM
Another crash prone roundabout is at 14th Street & Superior in Lincoln, Nebraska.  This triple-lane roundabout was completed in November 2012.  In the first 11 months of operations, crashes quadrupled from 27.3 to 119.8.  In October 2013, the roundabout was converted to a two-lane roundabout.  Since the conversion, annualized crashes have dropped to 40.4 (which is still 47% higher than it was before the roundabout was constructed).  Here’s an article discussing the roundabout in greater detail:

https://lincoln.ne.gov/city/mayor/media/2014/050114.htm

I have my doubts that the triple-lane roundabout currently under construction in Dublin, Ohio will see a reduction in total crashes (even though this is what the engineering manager of Dublin is predicting). Instead of learning from others mistakes, the City will forge ahead and construct it as a triple-lane roundabout.  A year later, the City will be perplexed why there are so many crashes at the roundabouts and hire a consultant to perform a safety audit.  The consultant, after being handed a big bag of money, will come to the conclusion that the roundabout should be reconfigured to a two-lane roundabout to reduce the total number of crashes.

Here are other examples of triple-lane roundabouts that have recently been reconfigured to two-lane roundabouts (look at historical imagery to see the changes):
https://www.google.com/maps/@42.5417215,-83.4000249,139m/data=!3m1!1e3
https://www.google.com/maps/@42.5422709,-83.3803509,139m/data=!3m1!1e3
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on May 22, 2015, 12:43:36 AM
Another crash prone roundabout is at 14th Street & Superior in Lincoln, Nebraska.  This triple-lane roundabout was completed in November 2012.  In the first 11 months of operations, crashes quadrupled from 27.3 to 119.8.  In October 2013, the roundabout was converted to a two-lane roundabout.  Since the conversion, annualized crashes have dropped to 40.4 (which is still 47% higher than it was before the roundabout was constructed).

They only gave it 11 months? Jesus. So immediate top-tier performance or bust? I think crashes would drop over time, no need to act so hastily.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on May 22, 2015, 10:27:01 AM
Another crash prone roundabout is at 14th Street & Superior in Lincoln, Nebraska.  This triple-lane roundabout was completed in November 2012.  In the first 11 months of operations, crashes quadrupled from 27.3 to 119.8.  In October 2013, the roundabout was converted to a two-lane roundabout.  Since the conversion, annualized crashes have dropped to 40.4 (which is still 47% higher than it was before the roundabout was constructed).

They only gave it 11 months? Jesus. So immediate top-tier performance or bust? I think crashes would drop over time, no need to act so hastily.

I think roundabouts with three entry lanes are growing out of favor.  Roundabouts with three entry lanes were constructed as part of the US41 project in Wisconsin.  From my understanding, Wisconsin has no plans to design new roundabouts with three entry lanes moving forward.  DaBigE might have more information regarding this based on some posts I've read of his.

Here are some videos of crashes that occurred at Maple & Drake (before the roundabout was converted to two entry lanes).  This roundabout had three entry lanes for several years before it was converted to two entry lanes: 

Title: Re: Crash prone 'modern roundabouts'
Post by: triplemultiplex on May 22, 2015, 11:27:30 AM
(297%) Canal & 25th Street (Milwaulkee, Wicsonsin):
https://www.google.com/maps/@43.0311071,-87.9434376,92m/data=!3m1!1e3

I have to wonder if the number of collisions at this intersection where one or more operator was intoxicated is significantly higher.  It's an exit route for fans leaving Brewer games and for patrons dumping off money at the Potowatomi Casino.  Two situations where drinking is encouraged.
It is said that drunks are more prone to side-swipe collisions and roundabouts are purposefully designed so if there is a crash, it will be low-angle and hopefully non-injurious.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on May 22, 2015, 01:27:05 PM
(297%) Canal & 25th Street (Milwaulkee, Wicsonsin):
https://www.google.com/maps/@43.0311071,-87.9434376,92m/data=!3m1!1e3

I have to wonder if the number of collisions at this intersection where one or more operator was intoxicated is significantly higher.  It's an exit route for fans leaving Brewer games and for patrons dumping off money at the Potowatomi Casino.  Two situations where drinking is encouraged.
It is said that drunks are more prone to side-swipe collisions and roundabouts are purposefully designed so if there is a crash, it will be low-angle and hopefully non-injurious.

Maybe, maybe not.  Livernois & Hamlin looks pretty innocuous yet that multi-lane roundabout saw over a 300% increase in total crashes. 
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on May 22, 2015, 02:50:18 PM
Another crash prone roundabout is at 14th Street & Superior in Lincoln, Nebraska.  This triple-lane roundabout was completed in November 2012.  In the first 11 months of operations, crashes quadrupled from 27.3 to 119.8.  In October 2013, the roundabout was converted to a two-lane roundabout.  Since the conversion, annualized crashes have dropped to 40.4 (which is still 47% higher than it was before the roundabout was constructed).

They only gave it 11 months? Jesus. So immediate top-tier performance or bust? I think crashes would drop over time, no need to act so hastily.

I think roundabouts with three entry lanes are growing out of favor.  Roundabouts with three entry lanes were constructed as part of the US41 project in Wisconsin.  From my understanding, Wisconsin has no plans to design new roundabouts with three entry lanes moving forward.  DaBigE might have more information regarding this based on some posts I've read of his.

Here are some videos of crashes that occurred at Maple & Drake (before the roundabout was converted to two entry lanes).  This roundabout had three entry lanes for several years before it was converted to two entry lanes: 

I'm fine with reducing the amount of lanes at roundabouts, but only if it's related to "too much capacity" instead of uneducated drivers (Bloomington Hills for example). Basic math suggests that more collisions occur at three lane roundabouts because three lane roundabouts can process more cars.
Title: Re: Crash prone 'modern roundabouts'
Post by: Quillz on May 22, 2015, 03:04:24 PM
Speaks more to the (in)flexibility of Michigan drivers than it does any inherent safety risk with roundabouts.  New roundabouts elsewhere have seen major drops in the number of crashes.
Yup, I'm actually writing a paper on roundabouts right now and this has largely been my conclusion, too. Driver behavior (i.e. being unfamiliar with how roundabouts work) is the main cause of accidents within a roundabout. The design in of itself has been consistently shown to be safer than most traditional signalized or stop controlled intersections.
Title: Crash prone 'modern roundabouts'
Post by: 6a on May 22, 2015, 05:44:28 PM
That's exactly what's being argued though.  Listen to what Jeannie Willis has to say about the expected safety benefits of a 3-lane roundabout currently under construction in Dublin, Ohio (6A touched on this roundabout previously in this thread).  What are the residents of Dublin to think if her predictions don't come to pass?  At that point, who cares right?  It will already be constructed.

Well, I can't speak for the specific roundabout being built; it's entirely possible that the existing intersection is so dangerous that it will reduce both the absolute frequency and severity of crashes (the data suggest some roundabouts do lead to less crashes than the intersections they replaced, and without systematically distinguishing between what the previous intersection type was it's hard to predict which will reduce crashes and which will lead to more crashes).

Assuming this is the intersection in question (https://www.google.com/maps/place/Dublin,+OH/@40.0995925,-83.1097332,250m/data=!3m1!1e3!4m2!3m1!1s0x8838ecc4d450a11f:0xc2176815689028!6m1!1e1), given the weird angle of the existing intersection I suspect the multilane roundabout will be an improvement on both scores.

That is indeed the intersection. It's hard to tell from that view obviously, but SB traffic goes up a somewhat sharp incline immediately before the light. I've mentioned that left turns are banned on the E-W route, and even with that and the SB bypass road it's the third worst crash intersection in the city. That's why I said...


Uh... Yes. 

Lordsutch said "I don't think anyone ever argued that roundabouts reduce collisions overall."  Jeannie Willis, the engineering manager for the City of Dublin, argued that "the frequency of the crashes will be reduced".


Here are some videos of crashes that occurred at Maple & Drake (before the roundabout was converted to two entry lanes).  This roundabout had three entry lanes for several years before it was converted to two entry lanes.

...I really do wonder if that will be the case in this instance. Call me an eternal optimist on this one. However, with the area already being quite well educated in roundabouts and I can only assume the quirky hill at the intersection being addressed, can it really get worse than #3 in the city? (As I type this my curiosity is piqued as to what the others are and how that one relates. Off to the bowels of the Internet...)

In those videos it appears the problem in that layout is three *through* lanes. The Dublin one is only three lanes in a quarter of the design (the SB bypass is being retained.) but only two of those are through lanes. The innermost lane will be restricted to left-turning traffic. If the mockup I posted is correct as to striping, it would appear the problem of a driver in the inner lane trying to go straight is addressed. Of course we all know lines don't keep cars in their place, as Mr. FedEx learned in your last video.

So, time will tell I suppose. I do admit to a raised eyebrow when I first saw the design and, if anything, it should have enough traffic (and our eyes) from the beginning to judge whether this design is genius or garbage.

Edit: here is the current view SB (speed limit 45)
(http://images.tapatalk-cdn.com/15/05/22/d8bfe789db5b2d53ed14437bbd8a83d2.jpg)

And NB. Note each direction gets an exclusive green phase.
(http://images.tapatalk-cdn.com/15/05/22/8dc28705647388d26b246f122bc65bf9.jpg)
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on May 22, 2015, 07:19:12 PM
I'm fine with reducing the amount of lanes at roundabouts, but only if it's related to "too much capacity" instead of uneducated drivers (Bloomington Hills for example). Basic math suggests that more collisions occur at three lane roundabouts because three lane roundabouts can process more cars.

Traffic volumes at 14th Street and Superior is down from the 2008 peak.  The 4 fold increase in crashes at this roundabout was not because more vehicles were navigating through the intersection.  Similarly, traffic volumes didn't drop overnight when the roundabout was converted from three lanes to two.
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on May 22, 2015, 09:42:46 PM
I'm fine with reducing the amount of lanes at roundabouts, but only if it's related to "too much capacity" instead of uneducated drivers (Bloomington Hills for example). Basic math suggests that more collisions occur at three lane roundabouts because three lane roundabouts can process more cars.

Traffic volumes at 14th Street and Superior is down from the 2008 peak.  The 4 fold increase in crashes at this roundabout was not because more vehicles were navigating through the intersection.  Similarly, traffic volumes didn't drop overnight when the roundabout was converted from three lanes to two.

It's not pure volume. It's throughput. The intersection is pushing a whole bunch more cars through every second compared to a smaller roundabout. There's basically a higher likelihood of a collision because there's more cars that can collide. You can avoid this by making the roundabout smaller, but the intersection capacity is likewise reduced.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on May 22, 2015, 10:33:01 PM
It's not pure volume. It's throughput. The intersection is pushing a whole bunch more cars through every second compared to a smaller roundabout. There's basically a higher likelihood of a collision because there's more cars that can collide. You can avoid this by making the roundabout smaller, but the intersection capacity is likewise reduced.

I got what you're saying now Jake.  You make a good point.
Title: Re: Crash prone 'modern roundabouts'
Post by: colinstu on May 23, 2015, 10:02:50 AM
(297%) Canal & 25th Street (Milwaulkee, Wicsonsin):
https://www.google.com/maps/@43.0311071,-87.9434376,92m/data=!3m1!1e3

I have to wonder if the number of collisions at this intersection where one or more operator was intoxicated is significantly higher.  It's an exit route for fans leaving Brewer games and for patrons dumping off money at the Potowatomi Casino.  Two situations where drinking is encouraged.
It is said that drunks are more prone to side-swipe collisions and roundabouts are purposefully designed so if there is a crash, it will be low-angle and hopefully non-injurious.

Umm... guys? I don't know where that 297% number is coming from but check out historical aerial imagery in Google Earth.

An intersection didn't even EXIST in that location before the roundabout, it was a a curved thru-road with a dirt road going over train tracks coming off the middle of it for the heavy industry that was present in the valley.
Canal St didn't even exist between the Brewers Parking lots and 25th St.

It was that way up until 2005 when Canal St between those two locations began as well as the roundabout taking shape. It wasn't completed until 2006, and more people probably didn't figure out that completed road existed until even later.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on May 23, 2015, 11:05:47 AM
Umm... guys? I don't know where that 297% number is coming from but check out historical aerial imagery in Google Earth.

The number came from a study funded by the Wisconsin Department of Transportation.  Looking at the historical aerials, I wouldn’t have included 25th Street & Canal in the analysis since the geometry of the before and after conditions is quite a bit different.  Recently, a three entry leg roundabout was constructed in Michigan that has seen a significant increase in total crashes.  I haven’t mentioned the location of the roundabout in this thread since it added another leg to the intersection that wasn’t previously there (and analyzing the before and after crash data wouldn’t be fair IMO).

Am I surprised that the Wisconsin Department of Transportation funded a report that analyzed a roundabout with dissimilar before and after conditions?  No.  This is the same agency who designed these crash prone multi-lane roundabouts to begin with.  To be fair, several of the roundabouts included in the report have similar before and after conditions.  If you take out the results of the 25th Street & Canal roundabout, the remaining multi-lane roundabouts saw an overall increase in crashes. 
Title: Re: Crash prone 'modern roundabouts'
Post by: DaBigE on May 25, 2015, 01:52:02 AM
I think roundabouts with three entry lanes are growing out of favor.  Roundabouts with three entry lanes were constructed as part of the US41 project in Wisconsin.  From my understanding, Wisconsin has no plans to design new roundabouts with three entry lanes moving forward.  DaBigE might have more information regarding this based on some posts I've read of his.

As far as I know, we're designing the last roundabout in Wisconsin that will have 2, three-lane entries. Yes, Wisconsin does now have a phobia/moratorium of any additional roundabouts with three-lane entries (with the exception of one region). Other states seem to be sharing the trepidation as well. We've worked on a few three-lane designs for other states, but many have ended up being scaled back. In many cases, three lane entries aren't needed for a long time, and depending on the analysis software/skill of the analyst, may never be needed. Attempting to design for 20-year forecasts can be very tricky/dangerous, especially for new developments.

There is a growing belief that many roundabouts are being over-designed, which leads to larger than necessary designs. The problem in the US is lack of reliable data (number of years of available of data), and correction factors that vary depending on what portion of the country you're in. If you read the WisDOT FDM section on roundabout design (FDM 11-26 (http://roadwaystandards.dot.wi.gov/standards/fdm/11-26.pdf) if you're interested), Wisconsin uses it's own critical headways and follow-up headway values for capacity analysis.

There's also big debate over how to handle trucks (semis - WB-62s, WB-67s): should they stay in-lane, and if so, where? Just on the entry (aka Case II)? Throughout the roundabout movement (Case III)? Neither (Case I)? That can also lead to larger than necessary designs > faster operating speeds > more crashes.

Am I surprised that the Wisconsin Department of Transportation funded a report that analyzed a roundabout with dissimilar before and after conditions?  No.  This is the same agency who designed these crash prone multi-lane roundabouts to begin with.  To be fair, several of the roundabouts included in the report have similar before and after conditions.  If you take out the results of the 25th Street & Canal roundabout, the remaining multi-lane roundabouts saw an overall increase in crashes.

All I am going to say on this is there's a lot of flaws that can be found in WisDOT's roundabout crash studies (Phase III is set to be released later this summer).

The take-home message has been severe injury/fatal crashes have seen significant decreases. Fender-benders (aka PDO crashes) have gone up significantly in multilane roundabouts. Having read through many crash narratives, the majority have been attributed to failure to yield or improper lane usage). The stupid maneuvers people try to pull...it's almost so common it ceases to amaze me any more.
Title: Re: Crash prone 'modern roundabouts'
Post by: froggie on May 25, 2015, 12:18:13 PM
DaBigE (and tradephoric too for that matter), have you looked into the research MnDOT completed last year on signage and striping with multilane roundabouts?  This is just one study of one multilane roundabout, but they found tweaking signage and striping led to significant decreases in the number of crashes caused by yield failures and improper lane usage:

http://www.dot.state.mn.us/research/TS/2014/201404TS.pdf (summary)

http://www.dot.state.mn.us/research/TS/2014/201404.pdf (study)
Title: Re: Crash prone 'modern roundabouts'
Post by: DaBigE on May 25, 2015, 11:48:50 PM
DaBigE (and tradephoric too for that matter), have you looked into the research MnDOT completed last year on signage and striping with multilane roundabouts?  This is just one study of one multilane roundabout, but they found tweaking signage and striping led to significant decreases in the number of crashes caused by yield failures and improper lane usage:

http://www.dot.state.mn.us/research/TS/2014/201404TS.pdf (summary)

http://www.dot.state.mn.us/research/TS/2014/201404.pdf (study)

Yes, I am fairly familiar with that study. My biggest issue with the study is that it's impossible to tell what had the most effect on driver behavior since they implemented two relatively significant changes at the same time. My gut says it was the change in signing, based driver observations on obeying markings as well as changes Madison, WI made to this roundabout (https://www.google.com/maps/@43.1212745,-89.2990561,191m/data=!3m1!1e3), after it was in the top 5 worst intersections in the city for crashes for several years. It has since dropped off the radar/top ten. Several signs were added; no pavement markings were changed. Unfortunately Google StreetView doesn't show them, but the city added a few lane reminder signs in the outside corners (one significant problem was crossing crashes at the exits), as well as a standard NO RIGHT TURN with a LEFT LANE plaque on the eastbound approach. Similar to my roundabout size comment, many [designers] think this roundabout is sized a bit too large, as speeds are quite high.

What's interesting about that MnDOT study is many of the changes they implemented closely mimic WisDOT standards for roundabout signing/marking (although we tend to favor overhead signing when possible, rather than ground-mount). I've worked on a couple Minnesota roundabouts and trying to implement overhead signs is a PITA.
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on May 26, 2015, 01:26:22 AM
Not sure what kind of signing might be helpful, but two additions that I think we could adopt from the UK:

1) Pavers indicating movement direction:

(http://www.mss-concrete.co.uk/mm/concrete-stone-cutting.jpg)

2) larger chevrons indicating movement direction:

(http://www.sabre-roads.org.uk/wiki/images/2/23/A9_Tore_Roundabout_-_Chevrons.jpg)

While I'm not entirely certain how relevant left turns are at roundabouts these days (most studies, which I'm sure cover the stats, confuse me to no end), I would think these practices would put a stop to it. I know number 1 has been used before (couldn't quote any examples, I'm just certain I've seen it) but number 2, while we use chevrons, I don't think we've ever used it to such an extent. Perhaps while we're at it, we ought to bring back the circular one-way sign.

DaBigE, despite my suggestions above, do you think there is such a thing as signage overload? If so, do you think it holds some relevance to this here conversation?
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on May 26, 2015, 11:56:11 AM
There's also big debate over how to handle trucks (semis - WB-62s, WB-67s): should they stay in-lane, and if so, where? Just on the entry (aka Case II)? Throughout the roundabout movement (Case III)? Neither (Case I)? That can also lead to larger than necessary designs > faster operating speeds > more crashes.

I’m very interested in this comment DaBigE.  Assuming there is an adequate entry deflection angle to slow the speed of traffic, wouldn’t larger roundabouts potentially result in fewer crashes and not more crashes?  With larger roundabouts, it’s easier to physically stay in your lane (likely resulting in fewer side-swipe crashes).  In addition, drivers might be able to judge available gaps in traffic better, since there is greater distance between legs.  With smaller roundabouts, entering drivers seem to be guessing what circulating vehicles intent is (since there isn’t as much distance between legs).   

The multi-lane roundabouts in SE Michigan that have seen significant increase in total crashes all seem to have smaller footprints (IE. central island diameters of 100 feet or less).  The roundabout at Ellsworth & State (that saw nearly a 10x increase in crashes) has a central island diameter of 100 feet.  Conversely, there are several examples of larger roundabouts in SE Michigan with central island diameters of greater than 150 feet that haven’t seen significant increases in crashes (with some seeing significant crash reductions).
Title: Re: Crash prone 'modern roundabouts'
Post by: DaBigE on May 26, 2015, 07:05:03 PM
There's also big debate over how to handle trucks (semis - WB-62s, WB-67s): should they stay in-lane, and if so, where? Just on the entry (aka Case II)? Throughout the roundabout movement (Case III)? Neither (Case I)? That can also lead to larger than necessary designs > faster operating speeds > more crashes.

I’m very interested in this comment DaBigE.  Assuming there is an adequate entry deflection angle to slow the speed of traffic, wouldn’t larger roundabouts potentially result in fewer crashes and not more crashes?  With larger roundabouts, it’s easier to physically stay in your lane (likely resulting in fewer side-swipe crashes).  In addition, drivers might be able to judge available gaps in traffic better, since there is greater distance between legs.  With smaller roundabouts, entering drivers seem to be guessing what circulating vehicles intent is (since there isn’t as much distance between legs).

While the amount of deflection is important, where and how the deflection ties into the circulatory is just as/more important. Many of the designs I've seen implemented lately are what we refer to as "hockey stick" designs... where the R1 entry curve that is too far upstream which results in a very flat entry at the circulatory (long tangent). These long tangents allow drivers to accelerate as they approach the yield point where they instead should be slowing down. Combine that with a larger roundabout diameter (ICD*), the faster the vehicle speeds though the roundabout (R1 & R2 speeds). The larger roundabouts may work safer when circulating volumes are higher or when the roundabout is operating closer to its capacity. However, the majority of crash reports I've seen occur during the off-peak times. During off-peak times, you might as well not paint any lines, as drivers tend to follow the fast-path though the roundabout. The faster the roundabout operates, the more willing drivers are to take smaller gaps, and crash doing so because they misjudged the speed of the circulating vehicle.

This is not to say that small roundabouts are the best. Like Goldilocks, there is a "just right" size. The general consensus regarding ICD is an inverse relationship between size and safety due to the direct relationship between size and speed.

The multi-lane roundabouts in SE Michigan that have seen significant increase in total crashes all seem to have smaller footprints (IE. central island diameters of 100 feet or less).  The roundabout at Ellsworth & State (that saw nearly a 10x increase in crashes) has a central island diameter of 100 feet.  Conversely, there are several examples of larger roundabouts in SE Michigan with central island diameters of greater than 150 feet that haven’t seen significant increases in crashes (with some seeing significant crash reductions).

A central island diameter of 100-feet is way to small even for a single lane roundabout. A typical minimum ICD for a multilane roundabout is approximately 160-feet. Assuming approximately 28-feet of pavement for the circulatory, that would net you a central island of 132-feet 104-feet (truck apron inclusive).

*NOTE: designers generally refer to the size of the roundabout based on the diameter to the face of the outside curb of the circulatory, or the inscribed circle diameter

**Edited to correct math error
Title: Re: Crash prone 'modern roundabouts'
Post by: DaBigE on May 26, 2015, 07:30:38 PM
DaBigE, despite my suggestions above, do you think there is such a thing as signage overload? If so, do you think it holds some relevance to this here conversation?

YES. That is precisely why there is minimum recommended spacing between signs in general and maximum recommended amounts of legend in a guide sign. I cringe a little every time I have to deal with an intersection of more than two or three routes. Post too many signs, and drivers will ignore them. This is why I don't like the Ped Xing sign being posted at every. single. crosswalk. For every sign you post, there is a perception-reaction time associated with it. Despite what some think, posting another sign will not correct an overall design flaw or lack of education.

I am a firm believer in less is more - to a point. The key is getting the important information to the driver at the right time. That is why I personally prefer overhead lane signage to post-mounted, especially in urban areas. Getting drivers into the appropriate lane early when approaching a roundabout is critical.

Not sure what kind of signing might be helpful, but two additions that I think we could adopt from the UK:

1) Pavers indicating movement direction:

(http://www.mss-concrete.co.uk/mm/concrete-stone-cutting.jpg)

This has been tried once or twice before, and the end result was a PITA to install and maintain. It's too subtle for many US drivers to comprehend. With so many central islands being used for public artwork, many think it's just part of the design. IMO, it's a waste of money.

Quote
2) larger chevrons indicating movement direction:

(http://www.sabre-roads.org.uk/wiki/images/2/23/A9_Tore_Roundabout_-_Chevrons.jpg)

In my experiences, wrong-way movements with regards to a roundabout appears to be a shrinking problem. Referencing the discussion with tradephoric, properly executed deflection should render these signs virtually useless. Improper yielding is the biggest concern, which is why WisDOT uses the plaque TO TRAFFIC FROM LEFT, with other states and municipalities using variants of that.

Perhaps while we're at it, we ought to bring back the circular one-way sign.

Testing may prove me wrong, but I don't think another style of sign is going to gain compliance. Only a vehicle with lights and siren seem to work.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on May 26, 2015, 10:05:53 PM
A central island diameter of 100-feet is way to small even for a single lane roundabout. A typical minimum ICD for a multilane roundabout is approximately 160-feet. Assuming approximately 28-feet of pavement for the circulatory, that would net you a central island of 132-feet (truck apron inclusive).

The top 5 highest crash frequency intersections in Oshkosh, Wisconsin are at multi-lane roundabouts with central island diameters of 100 feet or less.  Here is a table of the Oshkosh roundabouts with the construction year highlighted in yellow:

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Oshkosh%20rank_zps1dessqqv.png)
http://www2.ci.oshkosh.wi.us/WebLink8/0/doc/711055/Electronic.aspx

I’m starting to see a theme...  multi-lane roundabouts with central island diameters of 100 feet or less have high crash frequencies (especially at roundabouts with high AADT).  Nearly every roundabout cited in this thread (apart from the triple lane roundabout from Lincoln, Nebreska) has had a central island diameter of roughly 100 feet.
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on May 26, 2015, 10:35:31 PM
A central island diameter of 100-feet is way to small even for a single lane roundabout. A typical minimum ICD for a multilane roundabout is approximately 160-feet. Assuming approximately 28-feet of pavement for the circulatory, that would net you a central island of 132-feet (truck apron inclusive).

The top 5 highest crash frequency intersections in Oshkosh, Wisconsin are at multi-lane roundabouts with central island diameters of 100 feet or less.  Here is a table of the Oshkosh roundabouts with the construction year highlighted in yellow:

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Oshkosh%20rank_zps1dessqqv.png)
http://www2.ci.oshkosh.wi.us/WebLink8/0/doc/711055/Electronic.aspx

I’m starting to see a theme...  multi-lane roundabouts with central island diameters of 100 feet or less have high crash frequencies (especially at roundabouts with high AADT).

It would probably be fair to see a longer list, which will show both 100' diameter roundabouts that don't have high crash frequencies, and roundabouts with larger diameters and how they rank. 
Title: Re: Crash prone 'modern roundabouts'
Post by: DaBigE on May 26, 2015, 11:28:07 PM
A central island diameter of 100-feet is way to small even for a single lane roundabout. A typical minimum ICD for a multilane roundabout is approximately 160-feet. Assuming approximately 28-feet of pavement for the circulatory, that would net you a central island of 132-feet (truck apron inclusive).

The top 5 highest crash frequency intersections in Oshkosh, Wisconsin are at multi-lane roundabouts with central island diameters of 100 feet or less.  Here is a table of the Oshkosh roundabouts with the construction year highlighted in yellow:

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Oshkosh%20rank_zps1dessqqv.png)
http://www2.ci.oshkosh.wi.us/WebLink8/0/doc/711055/Electronic.aspx

I’m starting to see a theme...  multi-lane roundabouts with central island diameters of 100 feet or less have high crash frequencies (especially at roundabouts with high AADT).  Nearly every roundabout cited in this thread (apart from the triple lane roundabout from Lincoln, Nebreska) has had a central island diameter of roughly 100 feet.

And after correcting my math error (forgot I was working with a diameter, not a radius :pan:), the 100-foot central island falls right at the prescribed minimum for a multilane roundabout size - at least according to WisDOT and NCHRP Report 679. In fact, Report 679 suggests a minimum ICD as low as 150-feet. IIRC, Europe has even more compact roundabouts, yet not nearly the crash problem.
Title: Re: Crash prone 'modern roundabouts'
Post by: DaBigE on May 26, 2015, 11:45:23 PM
A central island diameter of 100-feet is way to small even for a single lane roundabout. A typical minimum ICD for a multilane roundabout is approximately 160-feet. Assuming approximately 28-feet of pavement for the circulatory, that would net you a central island of 132-feet (truck apron inclusive).

The top 5 highest crash frequency intersections in Oshkosh, Wisconsin are at multi-lane roundabouts with central island diameters of 100 feet or less.  Here is a table of the Oshkosh roundabouts with the construction year highlighted in yellow:

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Oshkosh%20rank_zps1dessqqv.png)
http://www2.ci.oshkosh.wi.us/WebLink8/0/doc/711055/Electronic.aspx

I’m starting to see a theme...  multi-lane roundabouts with central island diameters of 100 feet or less have high crash frequencies (especially at roundabouts with high AADT).

It would probably be fair to see a longer list, which will show both 100' diameter roundabouts that don't have high crash frequencies, and roundabouts with larger diameters and how they rank.

It would also be valuable to note that Washburn & 9th, Koeller & 9th are part of a corridor of 4 closely-spaced roundabouts. Frankly, I'm surprised to not see the roundabouts at Wis 21/I-41/Washburn/Koeller appear high on the list, as those are also similarly designed roundabouts, a few with 3-lane entries. Maybe they show up further down on the list...can't tell right now because I get a server error when attempting to use the link tradephoric provided. However, IIRC, Wis 21 wasn't opened until 2012 or early 2013.

Does anyone have crash data for Carmel, Indiana?
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on May 27, 2015, 03:05:59 PM
It would probably be fair to see a longer list, which will show both 100' diameter roundabouts that don't have high crash frequencies, and roundabouts with larger diameters and how they rank. 

Here is a list of 40 multi-lane roundabouts that I think could be meaningful to this conversation.  This was queried from a database of over 5,100 modern roundabouts.  This was the criteria used to query out the list:

-roundabouts constructed within the last 10 years
-all approaches have 2 entry lanes
-roundabouts have 4-legs
-main & side streets are major state or county routes (ie. likely high AADT roundabouts)
-interchange roundabouts (and frontage road roundabouts) not included

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/RBtest_zpsbkjmf4ri.png)

Now the hard part is finding accurate before/after crash data to make any type of analysis.  Here is a google KMZ file that includes the 40 roundabouts in the chart above:

http://www.mediafire.com/download/cd570rarros2c3g/Multi-Lane+Roundabouts+%28with+high+AADT%29.kmz

Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on May 27, 2015, 04:49:38 PM
Crashes up at multi-lane roundabout in Cheyenne, Wyoming:

http://www.wyomingnews.com/articles/2014/08/15/news/19local_08-15-14.txt#.VWYsqEYmlBI
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on May 27, 2015, 04:50:41 PM
Three of Madison's most crash prone intersections are roundabouts:

http://www.channel3000.com/news/Three-of-Madison-s-most-crash-prone-intersections-are-roundabouts/16170598
Title: Re: Crash prone 'modern roundabouts'
Post by: colinstu on May 27, 2015, 05:08:07 PM
I think one important factor that needs to be considered is the severity of the crashes, not the number of them. Assigning weights to different kinds of crashes to how commonly they occur to more accurately compare them. What also needs to be considered are traffic counts. If traffic at the intersection doubles... Well no doubt there will be more collisions. All these variables need to be leveled out to make any kind of meaningful comparison.

Roundabouts (properly designed) vs 4-way intersection aren't going to have head-on or t-bone collisions. While they may have more fender benders (and thus more "crashes") ... The severity of those (and risk of injury / death) is much lower. I'd rather have more safe accidents then less deadly accidents.
Title: Re: Crash prone 'modern roundabouts'
Post by: DaBigE on May 27, 2015, 05:26:35 PM
Three of Madison's most crash prone intersections are roundabouts:

http://www.channel3000.com/news/Three-of-Madison-s-most-crash-prone-intersections-are-roundabouts/16170598

That article is from 3 years ago. Virtually all of Madison's roundabouts are out of the top ten list in the report from last year.
Title: Re: Crash prone 'modern roundabouts'
Post by: english si on May 27, 2015, 05:32:36 PM
I'd rather have more safe accidents then less deadly accidents.
Stannis the mannis isn't happy! (sorry, images are small)
(https://s-media-cache-ak0.pinimg.com/236x/17/e1/8b/17e18b76f82272bc6d5d78bcec056a84.jpg)
(https://scontent.cdninstagram.com/hphotos-xaf1/t51.2885-15/s320x320/e15/11226885_818816364855265_1929643643_n.jpg)
"more safe" is "less deadly".

I think you meant that you'd rather have more, but safer, accidents than fewer, but deadlier, accidents.
Title: Re: Crash prone 'modern roundabouts'
Post by: colinstu on May 27, 2015, 05:35:24 PM
Yup that's what I mean. Phrasing. Figure it out. :P
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on May 27, 2015, 05:58:39 PM
Three of Madison's most crash prone intersections are roundabouts:

http://www.channel3000.com/news/Three-of-Madison-s-most-crash-prone-intersections-are-roundabouts/16170598

That article is from 3 years ago. Virtually all of Madison's roundabouts are out of the top ten list in the report from last year.

According to the article, none of the intersections were in the top 25 list before they were converted to roundabouts though.  I think the crash results are meaningful.  Keep in mind, this is around the time Rep. Craig introduced a bi-partison bill that would give more control to local communities to what roundabouts get built and less control to Madison bureaucrats.  Did the early crash results from Madison and Oshkosh play a part in that?  I think the public takes notice (and voice concerns to their elected officials) when they read articles stating that crashes have spiked after the completion of a roundabout. 
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on May 27, 2015, 07:49:36 PM
Excerpts from an article discussing New Berlin interchange roundabouts (http://www.newberlinnow.com/news/56607067.html):

Quote
In fact, new figures from the city show that drivers were more likely to have a crash in the Moorland Road/Rock Ridge roundabout last year than at any other major intersection in New Berlin.  There were 2.08 crashes per 1 million vehicles through the intersection, the highest crash rate among the top 25 New Berlin intersections in 2008.

^This double-lane roundabout has a central island diameter of 120 feet.

Quote
New Berlin's other roundabout, at Moorland Road and Interstate 43, had the third highest crash rate with 1.43 crashes per 1 million vehicles.

^This triple-lane roundabout has a central island diameter of 190 feet

The roundabout with the larger central island diameter has a lower crash frequency (1.43 crashes per 1 million vehicles vs. 2.08 crashes per 1 million vehicles).  Are bigger roundabouts better at lowering crash frequency?
Title: Re: Crash prone 'modern roundabouts'
Post by: english si on May 28, 2015, 05:30:32 AM
The roundabout with the larger central island diameter has a lower crash frequency (1.43 crashes per 1 million vehicles vs. 2.08 crashes per 1 million vehicles).  Are bigger roundabouts better at lowering crash frequency?
Depends - there comes a point where circulating traffic is going too fast and needs to be slowed down for safety and capacity's sake.

And of course, crashes are more likely to be severe on bigger islands due to the faster speeds. Still better than a signalised crossroads for that though.
Title: Re: Crash prone 'modern roundabouts'
Post by: DaBigE on May 28, 2015, 09:45:56 AM
Three of Madison's most crash prone intersections are roundabouts:

http://www.channel3000.com/news/Three-of-Madison-s-most-crash-prone-intersections-are-roundabouts/16170598

That article is from 3 years ago. Virtually all of Madison's roundabouts are out of the top ten list in the report from last year.

According to the article, none of the intersections were in the top 25 list before they were converted to roundabouts though.  I think the crash results are meaningful.  Keep in mind, this is around the time Rep. Craig introduced a bi-partison bill that would give more control to local communities to what roundabouts get built and less control to Madison bureaucrats.  Did the early crash results from Madison and Oshkosh play a part in that?  I think the public takes notice (and voice concerns to their elected officials) when they read articles stating that crashes have spiked after the completion of a roundabout.

Yes, the crash results are meaningful, all crash results are meaningful...especially more recent ones showing roundabouts are becoming safer (two roundabouts remained on the top-ten list for Madison, at least as of the 2013 data, but dropped in position): 2013 Madison Police Report (https://www.cityofmadison.com/police/documents/10MostDangerousIntersections2013.pdf), Madison.com 2014 News Story (http://host.madison.com/news/local/crime_and_courts/madison-s-worst-intersections-east-washington-and-stoughton-road-tops/article_c0acda33-4112-5cce-9eeb-1ed2d8edb19e.html). As both suggest, failure to yield and improper turn/lane usage top the list of reasons - two items that are not directly correlated with the size of the roundabout, but rather driver behavior. Two of the biggest prior offenders - the pair on Thompson Dr, dropped off the list after residing there for several years.

As for the failed legislation, when did adding more bureaucracy ever solve anything? Intersection projects are approved by the DOT, not by the legislators, however, they can persuade the DOT to increase the priority of a project. Many of the roundabouts that have been constructed (albeit mostly of the single-lane variety) have been for serious crash injury issues, which the roundabouts have largely cured. Locals already get a say and I know of at least a dozen projects that were changed because of local input. It doesn't help when people don't follow the process and decide to complain after the comment periods have passed. While I'm sure the crash records had some impact, the bigger reason is there still is a large hatred of all roundabouts, many times without logical reasoning. The funny thing is, survey after survey continues to show the tables completely turning after a roundabout has been opened to traffic, with the number of those not liking the roundabouts shrinking dramatically.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on May 28, 2015, 11:30:46 AM
Thank you for the links to the Madison crash reports DaBigE.  Unfortunately, the reports only include the top 30 crash prone intersections and neither Lien & Thompson, County Rd M & Valley View Rd, or Mineral Point & Valley View Rd were in the top 30 in the 2009 or 2010 reports.  Since they weren’t in the top 30, let’s assume then that intersections averaged 8 crashes per year before the roundabouts were constructed (which was how many crashes the #30 most crash prone intersection experienced in both the 2009 & 2010 crash reports).  What happened since the multi-lane roundabouts were constructed in Madison?

Lien Rd & Thomson Dr: constructed in 2010.  In 2011, it was the #1 most crash prone intersection in the region with 23 crashes.   Couldn’t find crash data from 2012 or 2013. 

County Rd M & Valley View Rd: constructed in 2010.  In 2011, it was the #3 most crash prone intersection in the region with 18 crashes.  In 2012 the crashes rose to 22 and in 2013 crashes rose to 25. 

Mineral Point & Pleasant View Rd: constructed in 2011.  In 2012, it was the #1 most crash prone intersection in the region with 46 crashes.  In 2013 crashes dropped to 30.

DaBigE, do you know where County Rd M & Valley View Rd currently stands in the ranking of most crash prone intersections in Madison?  The total number of crashes seem to be increasing year over year at this roundabout. 
Title: Re: Crash prone 'modern roundabouts'
Post by: DaBigE on May 28, 2015, 11:59:09 AM
Thank you for the links to the Madison crash reports DaBigE.  Unfortunately, the reports only include the top 30 crash prone intersections and neither Lien & Thompson, County Rd M & Valley View Rd, and Mineral Point & Valley View Rd were in the top 30 in the 2009 or 2010 reports.  Since they weren’t in the top 30, let’s assume then that intersections averaged 8 crashes per year before the roundabouts were constructed (which was how many crashes the #30 most crash prone intersection experienced in both the 2009 & 2010 crash reports).  What happened since the multi-lane roundabouts were constructed in Madison?

Lien Rd & Thomson Dr: constructed in 2010.  In 2011, it was the #1 most crash prone intersection in the region with 23 crashes.   Couldn’t find crash data from 2012 or 2013. 

County Rd M & Valley View Rd: constructed in 2010.  In 2011, it was the #3 most crash prone intersection in the region with 18 crashes.  In 2012 the crashes rose to 22 and in 2013 crashes rose to 25. 

Mineral Point & Pleasant View Rd: constructed in 2011.  In 2012, it was the #1 most crash prone intersection in the region with 46 crashes.  In 2013 crashes dropped to 30.

DaBigE, do you know where County Rd M & Valley View Rd currently stands in the ranking of most crash prone intersections in Madison?  The total number of crashes seem to be increasing year over year at this roundabout.

As far as I know, the 2014 data/report is not available yet. They were implementing some landscaping changes to try to get drivers to slow down further by selectively restrict their sight. I'm curious to find out how that has impacted driver behavior. Note that both of those west-side roundabouts have central islands 145-150-feet in diameter.

One must also keep in mind that got it's first modern roundabouts in 2004 (Thompson & Wis 30/Commercial Ave). Being on the far side of town, overall driver exposure to roundabouts was limited. The roundabouts at Mineral Point & CTH M were the first large roundabouts that drivers on the west side were exposed to. I'm curious to see the crash pattern for the newly-finished jug-handle intersection on the west side will reveal.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on May 28, 2015, 09:04:43 PM
As far as I know, the 2014 data/report is not available yet. They were implementing some landscaping changes to try to get drivers to slow down further by selectively restrict their sight. I'm curious to find out how that has impacted driver behavior. Note that both of those west-side roundabouts have central islands 145-150-feet in diameter.

It's not a fair comparison to begin with.  Pleasant View Road was constructed as part of the roundabout project so comparing the before/after crash data for these roundabouts is somewhat irrelevant.  I shouldn't have included it in the list of 40 (i didn't do a detailed before/after geometric comparison when compiling the list... it's a lot of data to go through!).    The fact that there was a big increase in crashes at these roundabouts isn't an indication that large central island diameters are more crash prone than smaller ones.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on May 28, 2015, 09:14:50 PM
A 5-leg roundabout in Valparaiso had 98 crashes in 2014.

(https://www.ci.valparaiso.in.us/images/pages/N1243/5%20Points%20Roundabout%20Rendering.jpg)

Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on May 29, 2015, 11:22:05 AM
The Insurance Institute for Highway Safety released a report in 2000 evaluating the safety of 24 intersections that were converted to roundabouts.  The report found the following:

Quote
The present study evaluated changes in motor vehicle crashes following conversion of 24 intersections from stop sign and traffic signal control to modern roundabouts. The settings, located in 8 states, were a mix of urban, suburban, and rural environments. A before-after study was conducted using the empirical Bayes approach, which accounts for regression to the mean. Overall, the empirical Bayes procedure estimated highly significant reductions of 39 percent for all crash severities combined and 76 percent for all injury crashes. Reductions in the numbers of fatal and incapacitating injury crashes were estimated to be about 90 percent.

http://safety.fhwa.dot.gov/intersection/resources/fhwasa09027/resources/Crash%20Reductions%20Following%20Installation%20of%20Roundabouts.pdf

The study was skewed towards evaluating single-lane roundabouts as only 9 of the 24 intersections evaluated were multi-lane roundabouts.  The 9 multi-lane roundabouts evaluated were all from Colorado and 6 of the 9 serviced interchanges along I-70.  The 3 non-interchange multi-lane roundabouts evaluated in the study were all along Avon Road in Avon, Colorado. When looking at aerials, there appears to be limited traffic generated along the side-street for 2 of the 3 roundabouts (IE. the side-street isn’t a major route).  Here is a list of all the roundabouts evaluated in the Insurance Institute study:

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/2000study_zpsvmsggp6l.png)

In the press release for the proposed multi-lane roundabout at State & Ellsworth, the Washtenaw County Road Commission cited a study with familiar looking safety numbers:

Quote
As stated by a 2011 report from the Insurance Institute of Highway Safety, 23 intersections that were converted into roundabouts experienced significant declines in accidents. Total crash frequency fell by approximately 40 percent; injury crash frequency fell by approximately 80 percent; and fatal crash frequency fell by approximately 90 percent.

http://www.wcroads.org/node/529

Citing a study that is skewed towards single-lane roundabouts when a major multi-lane roundabout is being proposed seems disingenuous.  Even the multi-lane roundabouts evaluated in the 2000 study are dissimilar to the roundabout that was being proposed for State & Ellsworth.  In the first year of operation, State & Ellsworth experienced roughly a 10x increase in crashes (not a 40% reduction).  Agencies shouldn't be implying that large multi-lane roundabouts will see a reduction in total crashes (and by citing studies that are skewed towards single-lane roundabouts, that's exactly what they are doing).
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on May 29, 2015, 03:46:03 PM
Here’s a traffic simulation of a roundabout currently under construction in Farmington Hills, Michigan at 14 Mile & Orchard Lake.  Over the last 5 years, the intersection has averaged 46 crashes per year.  This roundabout could experience a significant number of crashes once completed.  Does anybody want to wager how many crashes this roundabout will experience in FY2016?  The over/under is 180 crashes (I’ll bet the over). 

Title: Re: Crash prone 'modern roundabouts'
Post by: NE2 on May 29, 2015, 05:23:31 PM
PARCLO B4
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on May 29, 2015, 05:40:35 PM
Does anybody want to wager how many crashes this roundabout will experience in FY2016?  The over/under is 180 crashes (I’ll bet the over).

I'm going to guess 110 collisions in the first year, followed by 95 the second year, 83 the third year, 72 the fourth year, 63 the fifth year, and from then on, consistently dropping, just at an increasingly slower rate.

Again though, this isn't all about the number of collisions. It's about severity. As many have noted prior, it's better to have additional, safer collisions than fewer deadly collisions
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on May 29, 2015, 06:01:37 PM
Does anybody want to wager how many crashes this roundabout will experience in FY2016?  The over/under is 180 crashes (I’ll bet the over).

I'm going to guess 110 collisions in the first year, followed by 95 the second year, 83 the third year, 72 the fourth year, 63 the fifth year, and from then on, consistently dropping, just at an increasingly slower rate.

Again though, this isn't all about the number of collisions. It's about severity. As many have noted prior, it's better to have additional, safer collisions than fewer deadly collisions

If your prediction holds true, 14 Mile & Orchard Lake would go from the 64th most crash prone intersection in SE Michigan to #1 or #2 (fighting for the top spot with the roundabout at Ellsworth & State in Ann Arbor).  That's not good PR anyway you slice it.

http://semcog.org/Data-and-Maps/High-Frequency-Crash-Locations
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on May 29, 2015, 06:11:34 PM
Does anybody want to wager how many crashes this roundabout will experience in FY2016?  The over/under is 180 crashes (I’ll bet the over).

I'm going to guess 110 collisions in the first year, followed by 95 the second year, 83 the third year, 72 the fourth year, 63 the fifth year, and from then on, consistently dropping, just at an increasingly slower rate.

Again though, this isn't all about the number of collisions. It's about severity. As many have noted prior, it's better to have additional, safer collisions than fewer deadly collisions

If your prediction holds true, 14 Mile & Orchard Lake would go from the 64th most crash prone intersection in SE Michigan to #1 or #2 (fighting for the top spot with the roundabout at Ellsworth & State in Ann Arbor).  That's not good PR anyway you slice it.

http://semcog.org/Data-and-Maps/High-Frequency-Crash-Locations

If people aren't dying, that's good PR. Besides, what's the bad PR? "Collisions on the rise because people can't follow basic rules of the road"?
Title: Re: Crash prone 'modern roundabouts'
Post by: Mergingtraffic on May 29, 2015, 06:22:22 PM
The reason I dislike roundabouts or traffic circles is b/c of the YIELD.  Most drivers think YIELD means they don't have to stop even when traffic is in the circle.  It's only one reason, but a big reason. 

I notice that also on on-ramps to limited access highways with no merge time; there will be a YIELD sign and drivers just merge on causing accidents or forcing vehicles in the right of way to swerve.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on May 30, 2015, 10:49:16 AM
DaBigE (and tradephoric too for that matter), have you looked into the research MnDOT completed last year on signage and striping with multilane roundabouts?  This is just one study of one multilane roundabout, but they found tweaking signage and striping led to significant decreases in the number of crashes caused by yield failures and improper lane usage:

http://www.dot.state.mn.us/research/TS/2014/201404TS.pdf (summary)

http://www.dot.state.mn.us/research/TS/2014/201404.pdf (study)


I’ll echo what DaBigE said about the study.  There were too many variables at play to determine which changes had the biggest effect on driver behavior (sign and pavement marking type was changed, added additional signs, sign height was lowered, solid line extending from the yield line was lengthened).  This was readily acknowledged in the study:

Quote
Due to the nature of this study, implementing many changes at once, it is difficult to draw direct connections between individual sign and lane marking changes and the observed reductions in traffic violations. In addition, at the moment this represents a solidary experiment in one roundabout.

That said, the study suggests that the standard arrows may be less confusing to drivers and reduce the rate of turning violations when compared to fishhook arrows.  Why then did they revert back to fishhook pavement markings at 66th & Portland when looking at the most recent 2014 aerial?  Would having standard arrow pavement markings several hundred feet before the roundabout and fishhook pavement directly before entering the roundabout be less confusing to drivers?  I think it would add more confusion having a hodgepodge of arrow types like that.  It's hard to know what their thought process is with all the changes they are throwing at this roundabout.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on June 01, 2015, 07:13:13 PM
Another roundabout that has seen a significant increase in crashes is Homer Watson Boulevard and Block Line Road in Kitchener, Ontario.  Countermeasures including reducing the roundabout from 3-lanes to 2-lanes have been tried, but accidents keep going up.  The roundabout sees a significant amount of pedestrian traffic generated by St. Mary’s High school, as seen in the video below:


http://www.therecord.com/news-story/4960212-homer-watson-roundabout-continues-to-perplex-waterloo-region-politicians/
http://www.therecord.com/news-story/5648519-drivers-still-confused-by-homer-watson-roundabout-review-shows/
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on June 01, 2015, 08:43:11 PM
^Another roundabout is scheduled to be constructed in 2016 at Homer Watson & Ottawa Street.  This signalized intersection is one of the busiest in the Waterloo region and has averaged 44.8 crashes over the past 5 years (224 collisions total). 

Every high capacity roundabout cited in this thread has seen an increase in the total number of crashes upon completion, not a decrease.  The article below implies that Bob Henderson - manager of transportation engineering with the Region of Waterloo - believes there will be a reduction in total crashes once the roundabout at Homer Watson & Ottawa Street is completed in 2016.  Is Bob being too optimistic?

Quote
Henderson figures a roundabout will help cut crashes and reduce the severity of injuries since speeds in roundabouts are lower than at intersections with traffic lights.

http://metronews.ca/news/kitchener/1202881/waterloo-regions-most-dangerous-intersection-wont-see-improvements-until-2016/
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on June 02, 2015, 02:28:07 AM
Is Bob being too optimistic?

"Hi, my name is Bob, and I want everyone to know that there will be a massive increase in collisions once we are finished with this intersection".

That's not really engineer-speak. Truth is, collisions will go up but fatal or severe collisions will drop. Engineers should stop talking about the number of collisions. Instead, they should promote a new roundabout by promoting the large drop in fatal and/or serious collisions that roundabouts have repeatedly been shown to cut down on.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on June 02, 2015, 07:59:50 AM
Is Bob being too optimistic?

"Hi, my name is Bob, and I want everyone to know that there will be a massive increase in collisions once we are finished with this intersection".

That's not really engineer-speak. Truth is, collisions will go up but fatal or severe collisions will drop. Engineers should stop talking about the number of collisions. Instead, they should promote a new roundabout by promoting the large drop in fatal and/or serious collisions that roundabouts have repeatedly been shown to cut down on.

Here is an article that compares the safety of 17 roundabouts to 395 traffic signals in the Waterloo region.   It came to the following conclusion:

Quote
•At mid-sized intersections, the average traffic light and roundabout each saw one injury-causing collision. The roundabout saw 10 total collisions. The traffic light saw four. A mid-sized intersection sees between 10,000 and 25,000 vehicles per day.

•At busier intersections, the average traffic light and roundabout each saw three injury-causing collisions. The roundabout saw 26 total collisions. The traffic light saw 12. A busier intersection sees more than 25,000 vehicles per day.

•Traffic lights saw one person killed in 2013 (a pedestrian) while roundabouts had no deaths.

http://www.therecord.com/news-story/5217030-roundabouts-crashes-injuries-double-in-5-years-in-waterloo-region/

Roundabouts saw roughly the same amount of injury crashes as the traffic signals yet double the number of total crashes.  Other individual roundabouts cited in this thread have seen an increase in injury crashes.  The roundabout at State & Ellsworth in Ann Arbor (constructed in 2013) averaged 1.66 injury crashes the 3 years prior to the roundabout and saw 6 injury crashes the 1st year after the roundabout.  If you see a dramatic rise in total crashes there’s no guarantee you are going to see a drop in injury crashes.

http://semcog.org/Data-and-Maps/High-Frequency-Crash-Locations/Point_Id/81016689/view/RoadIntersectionCrashDetail
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on June 02, 2015, 08:37:24 AM
Is Bob being too optimistic?

"Hi, my name is Bob, and I want everyone to know that there will be a massive increase in collisions once we are finished with this intersection".

That's not really engineer-speak. Truth is, collisions will go up but fatal or severe collisions will drop. Engineers should stop talking about the number of collisions. Instead, they should promote a new roundabout by promoting the large drop in fatal and/or serious collisions that roundabouts have repeatedly been shown to cut down on.

A *large* drop in fatals/serious conditions? Maybe a drop, but if there's only a few of these accidents a year, how can there be a large drop?

However, there shoudn't be an increase in any type of accident.
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on June 02, 2015, 12:26:57 PM
A *large* drop in fatals/serious conditions? Maybe a drop, but if there's only a few of these accidents a year, how can there be a large drop?

Size is relative. If there were two fatal collisions, and 5 serious collisions in one year, followed by none of either after a roundabout is constructed, that's a significant drop. Perhaps not large, I'll give you that, but certainly notable.

However, there shoudn't be an increase in any type of accident.

That's what I thought prior to this thread, but at least in some areas of the country, that doesn't seem to be the case.

With that said, I still believe that driver familiarity is key for roundabouts to be successful. So, I'm holding back the angst against them for at least 20 years. Or so.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on June 02, 2015, 08:28:03 PM
A multi-lane roundabout in Rockford, Illinois has seen accidents jump from 3 crashes to 42 crashes when comparing the 6 month before/after crash data.  The roundabout has a central island diameter of 100 feet (roundabouts with the highest increases in crashes seem to have central island diameters of 100 feet or less…. larger diameter roundabouts are seeing increases in total crashes as well, but not the same extent as the smaller diameter ones). 

(http://www.mtjengineering.com/wp-content/uploads/2013/10/Rockfordfeat.jpg)

Quote
In the first six months of 2012 - before the roundabout was built -- just three accidents were reported at Auburn and Main. But in the first six months of 2014, that number shot up to 42 at the new roundabout, 14 times the number of accidents in the intersection compared to the same time period two years earlier.

And it's getting worse. Forty nine crashes were reported in the second six months of 2014, according to police, a more than 15% increase over the previous six months. But since the roundabout is not going anywhere, police are urging drivers to use extra caution when entering the circle. "If you pull up to the roundabout to make your own entry, you have to yield to cars that are already coming in there. Even though they are coming from the left, you have to yield to cars that are already in there and allow them to proceed through."

http://www.mystateline.com/fulltext-news/d/story/accident-rate-at-rockfords-wreck-it-roundabout-get/39721/pqAHhMWENES63uy-ujKlgg
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on June 02, 2015, 09:00:05 PM
Accident increases at roundabouts have DOT re-thinking

http://www.keprtv.com/news/local/Accident-increases-at-roundabouts-have-DOT-re-thinking-286719871.html
Title: Re: Crash prone 'modern roundabouts'
Post by: Brian556 on June 02, 2015, 09:14:24 PM
Wonder if they will turn out to be a fad like clearview?
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on June 02, 2015, 09:28:14 PM
Accident increases at roundabouts have DOT re-thinking

http://www.keprtv.com/news/local/Accident-increases-at-roundabouts-have-DOT-re-thinking-286719871.html

That might be the first example I've seen of WSDOT redesigning a roundabout. Usually they don't touch them, and instead spend money on educational campaigns. All told, I'm disappointed that WSDOT feels the need to change anything. I say, leave the roundabout alone for another ten years and come back. If anything, the total number of vehicles filtering through the intersection has been steadily increasing since they rebuilt the junction 8 years ago (between 2000 and 2014, the population of the area increased about 45%), which wouldn't correlate to a decrease in collisions.

Wonder if they will turn out to be a fad like clearview?

The number of roundabouts that see an increase in collisions are greatly overshadowed by the number that do not. So no, definitely not.
Title: Re: Crash prone 'modern roundabouts'
Post by: froggie on June 02, 2015, 11:09:56 PM
Multi-lane roundabouts might be reconsidered, but I highly doubt single-lane roundabouts will "turn out to be a fad".  The safety benefits are very well documented, even within the literature and numbers that tradephoric has been posting in recent weeks.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on June 03, 2015, 10:11:45 AM
In a previous post, I queried out 40 multi-lane roundabouts that have 2-entry lanes for all 4-legs (ie. the roundabouts in America that likely have the highest traffic volumes).  I’ve tracked down before/after crash data for 14 of them.  The excel file includes data links to articles/publications where the data was obtained.

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/RBDATASummary_zpsg7upbybr.png)
http://www.mediafire.com/view/p0u5ovrupr0175m/Multi-lane_roundabout_crashes.xlsx

The takeaway is that smaller roundabouts seem to be more accident prone than larger roundabouts.  Would there have been 171 crashes at State & Ellsworth if the roundabout was constructed with a central island diameter of 140’ as opposed to 100’?  This thread wasn't meant to bash roundabouts but to discuss ways to reduce the crash frequency at the highest AADT roundabouts.  My thought is make them just a little bit bigger.

Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on June 03, 2015, 10:58:02 AM
I held back on saying anything, and while I don't have any actual documentation, I want to know why these dual-lane roundabouts are having so many accidents when accidents at Jersey traffic circles, many of which are at least 2 lanes wide with no lane markings and little if any signed traffic control have fewer problems. 

The main reason Jersey circles have been removed wasn't because of accidents, but more so due to the congestion with so much traffic trying to use them.  Heck, many of these circles not only have the normal roads entering/exiting them, but business driveways enter and exit directly from them too.

Title: Re: Crash prone 'modern roundabouts'
Post by: Bickendan on June 03, 2015, 12:08:56 PM
Maybe all the Yield signs should be swapped out with full on Stop signs.
Seems to be drivers don't know what 'yield' means.
Title: Re: Crash prone 'modern roundabouts'
Post by: lordsutch on June 03, 2015, 12:55:53 PM
Maybe all the Yield signs should be swapped out with full on Stop signs.
Seems to be drivers don't know what 'yield' means.

Their first collision or near-miss will educate them nicely.
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on June 03, 2015, 01:09:32 PM
Maybe all the Yield signs should be swapped out with full on Stop signs.
Seems to be drivers don't know what 'yield' means.

Their first collision or near-miss will educate them nicely.

That doesn't help the guy that had the right of way that is now involved in an accident, delaying or missing whatever activity they were trying to get to, and now have to deal with insurance, car issues, medical issues, job related issues, etc, etc, etc.

How was he educated? 
Title: Re: Crash prone 'modern roundabouts'
Post by: Bickendan on June 03, 2015, 02:22:06 PM
Maybe all the Yield signs should be swapped out with full on Stop signs.
Seems to be drivers don't know what 'yield' means.

Their first collision or near-miss will educate them nicely.

That doesn't help the guy that had the right of way that is now involved in an accident, delaying or missing whatever activity they were trying to get to, and now have to deal with insurance, car issues, medical issues, job related issues, etc, etc, etc.

How was he educated? 
He gets an unfortunate and unneeded education in the intricacies of insurance claims.

Seriously though, stop signs at roundabouts. Coe Circle (NE 39th AveCésar Chavez Blvd and Glisan St in Portland) has been there since before the 1920s and I don't recall any incidents there since I moved to Portland in 94. While not the conventional multi-lane setup (right lane in all directions is right turn only so buses can stop at the gore islands), it does use stop signs to control traffic.
Title: Re: Crash prone 'modern roundabouts'
Post by: lordsutch on June 03, 2015, 02:25:38 PM
Seriously though, stop signs at roundabouts. Coe Circle (NE 39th AveCésar Chavez Blvd and Glisan St in Portland) has been there since before the 1920s and I don't recall any incidents there since I moved to Portland in 94. While not the conventional multi-lane setup (right lane in all directions is right turn only so buses can stop at the gore islands), it does use stop signs to control traffic.

In practice, are they treated as typical American "sure, roll through the stop sign at 5 mph as long as you tap your brakes" stops (i.e. what "yield/give way" actually means in the rest of the world), or are they real stops like European stop signs?
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on June 03, 2015, 02:34:53 PM
I held back on saying anything, and while I don't have any actual documentation, I want to know why these dual-lane roundabouts are having so many accidents when accidents at Jersey traffic circles, many of which are at least 2 lanes wide with no lane markings and little if any signed traffic control have fewer problems. 

The main reason Jersey circles have been removed wasn't because of accidents, but more so due to the congestion with so much traffic trying to use them.  Heck, many of these circles not only have the normal roads entering/exiting them, but business driveways enter and exit directly from them too.

New Jersey's rotaries probably work well because drivers are familiar with the intersections, and the legal maneuvers that can be performed at them. That's why I am personally not ready to give up on multi-lane roundabouts anytime soon. I think, given enough time, the overall number of collisions will drop off.

Many of the new modern roundabouts have been placed where there was no intersection before, so through traffic is probably not used to having to yield to other traffic, so they just keep on trucking (maybe).
Title: Re: Crash prone 'modern roundabouts'
Post by: Bickendan on June 03, 2015, 02:44:38 PM
Seriously though, stop signs at roundabouts. Coe Circle (NE 39th AveCésar Chavez Blvd and Glisan St in Portland) has been there since before the 1920s and I don't recall any incidents there since I moved to Portland in 94. While not the conventional multi-lane setup (right lane in all directions is right turn only so buses can stop at the gore islands), it does use stop signs to control traffic.

In practice, are they treated as typical American "sure, roll through the stop sign at 5 mph as long as you tap your brakes" stops (i.e. what "yield/give way" actually means in the rest of the world), or are they real stops like European stop signs?
It's dependent how heavy traffic in the circle is. As mentioned up thread, the advertising panels TriMet uses on their bus shelters in the gore points annoyingly obstruct line of sight, so drivers will cautiously creep past the stop sign to check for traffic on their left and wait there for a break. Bikers have the hardest time in the circle because it's built onto a hill (northbound 39th is uphill through the circle).
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on June 05, 2015, 11:01:36 AM
The Phase 2 roundabout study funded by the Wisconsin Department of Transportation analyzed 30 roundabouts built in 2008 or before (15 single-lane, 11 multi-lane, 4 spiral).  This was the main finding of the study:

Quote
Wisconsin roundabouts had an estimated 12 percent increase in total crashes and a 38 percent decrease in injury crashes.

Below is a KMZ file of the 30 Wisconsin roundabouts analyzed and a link to the study.

KMZ FILE:  http://www.mediafire.com/download/9oyt92teh4ee09y/Wisconsin+Roundabout+Study+%28Phase+2%29.kmz
STUDY:  http://www.topslab.wisc.edu/programs/safety/projects/roundabouts/WI%20Roundabout%20Evaluation%20FINAL%20REPORT%20-%20Phase%202.pdf


A few potential trends that can be seen when analyzing the KMZ/Study:

1.  Bigger is better.  Roundabouts with larger central island diameters perform better, on average, than roundabouts with smaller central island diameters.  Of the 4 roundabouts with a central island diameter of 120’ or greater, all saw a reduction in total crashes.

2.  Crashes are lower at interchange roundabouts.  The majority of the multi-lane roundabouts that saw a reduction in total crashes were at interchanges.

3.  Spiral roundabouts seem to perform better, on average, than non-spiral roundabouts. 
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on June 05, 2015, 01:28:08 PM
All I am going to say on this is there's a lot of flaws that can be found in WisDOT's roundabout crash studies (Phase III is set to be released later this summer).

DaBigE, do you know if Phase III is going to include more recent roundabouts constructed since 2008?  Wisconsin has aggressively been constructing higher capacity roundabouts more recently.  Today, there are at least 7 roundabouts in Wisconsin that have 3-circulating lanes (in 2008 there were none).  It would be interesting to see a study that analyzed the higher capacity roundabouts in Wisconsin that have been constructed recently.  Hopefully they can include roundabouts constructed in 2009, 2010, and 2011 in their next study.

Title: Re: Crash prone 'modern roundabouts'
Post by: DaBigE on June 06, 2015, 04:20:34 PM
All I am going to say on this is there's a lot of flaws that can be found in WisDOT's roundabout crash studies (Phase III is set to be released later this summer).

DaBigE, do you know if Phase III is going to include more recent roundabouts constructed since 2008?  Wisconsin has aggressively been constructing higher capacity roundabouts more recently.  Today, there are at least 7 roundabouts in Wisconsin that have 3-circulating lanes (in 2008 there were none).  It would be interesting to see a study that analyzed the higher capacity roundabouts in Wisconsin that have been constructed recently.  Hopefully they can include roundabouts constructed in 2009, 2010, and 2011 in their next study.

Yes, it will, according to the ITE presentation I attended back in April, it will cover roundabouts built thru 2009.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on June 09, 2015, 12:37:20 PM
I held back on saying anything, and while I don't have any actual documentation, I want to know why these dual-lane roundabouts are having so many accidents when accidents at Jersey traffic circles, many of which are at least 2 lanes wide with no lane markings and little if any signed traffic control have fewer problems. 

The main reason Jersey circles have been removed wasn't because of accidents, but more so due to the congestion with so much traffic trying to use them.  Heck, many of these circles not only have the normal roads entering/exiting them, but business driveways enter and exit directly from them too.



There's little evidence to suggest that traffic circles perform better than modern roundabouts.  According to the article below, when a traffic circle in Augusta, Maine was converted to a modern roundabout the intersection saw a 60% reduction in total crashes. 

http://www.pressherald.com/2013/04/17/terms-for-traffic-circles-cause-confusion_2013-04-18/
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on June 24, 2015, 10:07:37 AM
The Wisconsin and Michigan experiences that tradephoric commented on are the general opposite of Minnesota's experience, at least anecdotally as I don't think MnDOT has done a comprehensive study yet.  They have studied a few roundabouts, including a rural roundabout in particular (on MN 13 in Scott County), built in response to multiple fatal crashes, where there were HUGE declines in overall crashes after the roundabout was completed.  There's also a study documenting a multilane roundabout in Richfield that did see a high number of crashes (there wasn't really anything to compare it to pre-construction), but after tweaking with signage and striping saw crashes and "illegal turns" (i.e. turning left from the outer lane) decrease by about half.  This Richfield study/research may hold the key to getting better results out of multilane roundabouts.

In 2014, Andrew Plowman presented a presentation during the 4th Annual International Conference on Roundabouts detailing crash rates of 12 multi-lane roundabouts in Minnesota:

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/MNRBdata_zpsvkjdst9f.png)
http://teachamerica.com/RAB14/RAB1410APlowman/index.htm

*They found that 2x2 roundabouts have higher crash rates than 2x1 roundabouts.  Interestingly, the roundabouts at Bailey/Radio & Broadway/Lake have since been converted from 2x2 roundabouts to 2x1 roundabouts. 

*The 2x1 roundabout with the highest crash rate was at Diffley & Rahn.  This roundabout has the smallest central island diameter of any roundabout analyzed in the study (only 83 feet).  I’ve been hammering on that roundabouts with small diameters seem to be more accident prone than roundabouts with larger diameters and Diffley & Rahn seems to support that point.
Title: Re: Crash prone 'modern roundabouts'
Post by: Rothman on June 24, 2015, 12:02:26 PM
All I know is that the 2 x 2 roundabouts around here are prone to senile old people in the right lane of the roundabout continuing around the roundabout (ignoring the striping) and smashing into people following the striping from the left lane (i.e., exiting the roundabout).

See here for an example (https://goo.gl/maps/bX1wR).
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on June 24, 2015, 02:54:01 PM
All I know is that the 2 x 2 roundabouts around here are prone to senile old people in the right lane of the roundabout continuing around the roundabout (ignoring the striping) and smashing into people following the striping from the left lane (i.e., exiting the roundabout).

See here for an example (https://goo.gl/maps/bX1wR).

The roundabout is striped as a spiral roundabout yet the central island is circular (the central island isn’t designed to be a spiral roundabout).   The red path driver is following the path of least resistance to make a left turn through the roundabout.  The green path driver is doing everything right yet is liable to get sideswiped by the red path driver. 

Bethlehem, NY (New Scotland Road and Route 140)
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/NYRB_zpsmnpyxdmi.png)

Here’s an almost identical design of a 2x2 roundabout in Malta, NY.  Notice how the spiral dashes are faded in the aerial.  Even if they spiral dashes aren’t faded, the red path driver is going to cheat (as seen in the streetview image…the blue SUV is debating where the silver Honda is heading).

Malta, NY (Route 9, Route 67 and Dunning Street)
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/NYRBMalta_zpsifwwmbgh.png)
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/SVMalta_zpspdoii1ub.png)

Quote
In Malta, the roundabout at Route 9, Route 67 and Dunning Street went from an average of 7.8 crashes a year before the rotary to 45.7 a year afterward. In Bethlehem, the number of accidents at New Scotland Road and Route 140 jumped from an average of 9.6 a year to 38.3.
http://www.insurancejournal.com/news/east/2011/06/28/204259.htm

Moral of the story... spiral roundabouts should have properly designed central islands (and shouldn't rely on pavement markings to do the job). 

Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on June 25, 2015, 07:51:33 AM
The New York roundabouts in Bethlehem and Malta have nearly identical designs.  The biggest difference is size.

103 ft roundabout (Malta) = 445% increase in crashes
130 ft roundabout (Bethlehem) = 299% increase in crashes

IMO, both of these roundabouts have similar design flaws but the Bethlehem roundabout still performed better (even as traffic volume likely increased more at the Bethlehem roundabout since a lot of development took place as part of that roundabout project). 

Title: Re: Crash prone 'modern roundabouts'
Post by: Rothman on June 25, 2015, 01:04:27 PM
Oh, don't get me wrong: The Slingerlands roundabouts are much much much much much much better than the traffic signals that they replaced.  I just wish our drivers were trained well enough to read the signs and pavement markings!

Fun fact about the Malta roundabouts:  I was at ITSNY one year long ago where the Chief Operations Officer of NYSDOT spoke.  He brought up the Malta roundabouts and said, "You've got five roundabouts within a half mile!  We'll see how that works out for you!"  To this day, I have no idea who exactly he was talking to (Region 1?  Well, didn't he approve of the project himself, being the COO? Whaaaat? :D), but he had a tendency to sort of get lost in his sermons. :D
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on June 25, 2015, 03:19:53 PM
Oh, don't get me wrong: The Slingerlands roundabouts are much much much much much much better than the traffic signals that they replaced. I just wish our drivers were trained well enough to read the signs and pavement markings!

The problem is the pavement markings are so faded in that Malta roundabout aerial that an unfamiliar driver would have no idea that they are suppose to divert to the outside lane during the left turn maneuver.  With those faded spiral markings, I can absolutely see myself being that "red path" driver. 

Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on June 25, 2015, 05:39:58 PM
Oh, don't get me wrong: The Slingerlands roundabouts are much much much much much much better than the traffic signals that they replaced. I just wish our drivers were trained well enough to read the signs and pavement markings!

The problem is the pavement markings are so faded in that Malta roundabout aerial that an unfamiliar driver would have no idea that they are suppose to divert to the outside lane during the left turn maneuver.  With those faded spiral markings, I can absolutely see myself being that "red path" driver.

Perhaps if they opened up the closed lanes, it wouldn't be a big deal.
Title: Re: Crash prone 'modern roundabouts'
Post by: iBallasticwolf2 on June 25, 2015, 06:46:47 PM
I think these crash prone factors in modern roundabouts can be mostly fixed if:
1. Lane markings were kept easily seeable.
2. The right type of island is used. (Ex. Not using a circular island on a spiral roundabout.)
3. Island widths are higher. It seems that roundabouts with higher island widths have a smaller increase of accidents then roundabouts with lower island widths.
4. Drivers are taught you to drive these roundabouts better. We all know driver's driving skills deteriorate alot and half of them were taught before roundabouts were common.
Title: Re: Crash prone 'modern roundabouts'
Post by: Sykotyk on June 25, 2015, 10:49:06 PM
Early signage is key. You don't want sensory overload for people just as they enter the roundabout. You want them to know which lane they need to be in for which direction they plan on continuing. Generally, I think roundabouts should only be used for low-volume roads meeting eachother where a four-way stop or simple traffic light was the optimal former solution. The problem is in heavy traffic uses, roundabouts lose their 'flow' and it becomes a race to get into the traffic circle first so you don't have to stop, even if it's a bit dangerous or acceleration takes place.

I've never dealt with a three-lane entry that I can recall, and I don't want to. Enough people fail to use the two-lane ones properly. Which is sad, because misusing a roundabout should carry with it the same general emphasis as running a red light, or turning left before oncoming traffic. Yet, to many, that 'YIELD' sign means they get to go if they take the road first.

Going back on it, that's part of the problem. The Yield signs aren't being properly followed. If there's a four-entry roundabout with four yield signs, the second car in line does not get to go because the car in front of them went. When traffic builds to that point, it basically assumes the role of a four-way stop with the entry-points cycling in a (vehicle to the right goes first) and each car at the yield sign going one at a time. Instead it's "there's 5 cars in line at this yield sign, so all 5 get to go at once".
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on June 29, 2015, 08:40:06 PM
An example of a how a dominant leg at a roundabout can make it difficult for traffic at other legs to enter the roundabout (especially for semi's).

Title: Re: Crash prone 'modern roundabouts'
Post by: Brian556 on June 29, 2015, 09:04:26 PM
Quotew from        :
Quote
An example of a how a dominant leg at a roundabout can make it difficult for traffic at other legs to enter the roundabout (especially for semi's).

This is very true. When one leg has a very high volume, traffic on other legs does not get fair opportunity to enter the roundabout.
The southern one in Windermere FL defiantly has this problem. It seems pretty ridiculous, and unfair, to have to sit and wait a long time just to enter the roundabout.
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on June 29, 2015, 11:06:57 PM
An example of a how a dominant leg at a roundabout can make it difficult for traffic at other legs to enter the roundabout (especially for semi's).

This is very true. When one leg has a very high volume, traffic on other legs does not get fair opportunity to enter the roundabout.
The southern one in Windermere FL defiantly has this problem. It seems pretty ridiculous, and unfair, to have to sit and wait a long time just to enter the roundabout.

But this is kind of how roundabouts work...?

In regards to the video, at no point do any of the legs get unreasonably congested. This is not a very good example, tradephoric, if you're looking for a roundabout with "unfair" entry volumes.
Title: Re: Crash prone 'modern roundabouts'
Post by: lordsutch on June 29, 2015, 11:27:05 PM
The experience in the UK (where very high AADT is tolerated before improvements are made, particularly in rural and suburban areas, compared to the US) is that you can end up with situations like that even in a single-lane roundabout, particularly when there isn't enough traffic looping around to break up entry from one direction. The UK solution is almost always signalization, and when that doesn't work, adding some sort of flyover while keeping the signalized roundabout to continue to annoy everyone else. But this tends to happen at intersections that, by US standards, would be something like LOS G or H if the scale went that high.

Notorious example: A1-A421 Black Cat (https://en.wikipedia.org/wiki/Black_Cat_Roundabout) (see also: here (http://www.cbrd.co.uk/badjunctions/1-421/); in most of the US, it'd have been rebuilt as a Y-split or trumpet in the 1960s or 70s. Hell, the A1 would have been rebuilt properly as a freeway on a new alignment with a full interchange with the cheapo-freeway A421.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on June 30, 2015, 09:28:47 AM
An example of a how a dominant leg at a roundabout can make it difficult for traffic at other legs to enter the roundabout (especially for semi's).

This is very true. When one leg has a very high volume, traffic on other legs does not get fair opportunity to enter the roundabout.
The southern one in Windermere FL defiantly has this problem. It seems pretty ridiculous, and unfair, to have to sit and wait a long time just to enter the roundabout.
In regards to the video, at no point do any of the legs get unreasonably congested. This is not a very good example, tradephoric, if you're looking for a roundabout with "unfair" entry volumes.

The video shows some sweet 4k drone video of a spiral roundabout in action, if nothing else.  It probably wasn't the best example of a roundabout with uneven volumes but the point is still valid.  There is a roundabout by me where traffic on the heaviest leg experiences 20 second delays during the peak rush while adjacent legs experience 20 minute delays.  Traffic on the heaviest leg just overtakes the roundabout making it difficult for traffic on other legs to enter (especially tractor trailers).

Here's the roundabout in question.  The NB leg is the dominant movement, causing large backups on the WB leg during peak rush. 

https://www.google.com/maps/@42.5544792,-83.4485635,303m/data=!3m1!1e3
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on June 30, 2015, 09:34:47 AM
An example of a how a dominant leg at a roundabout can make it difficult for traffic at other legs to enter the roundabout (especially for semi's).

This is very true. When one leg has a very high volume, traffic on other legs does not get fair opportunity to enter the roundabout.
The southern one in Windermere FL defiantly has this problem. It seems pretty ridiculous, and unfair, to have to sit and wait a long time just to enter the roundabout.
In regards to the video, at no point do any of the legs get unreasonably congested. This is not a very good example, tradephoric, if you're looking for a roundabout with "unfair" entry volumes.

The video shows some sweet 4k drone video of a spiral roundabout in action, if nothing else.  It probably wasn't the best example of a roundabout with uneven volumes but the point is still valid.  There is a roundabout by me where traffic on the heaviest leg experiences 20 second delays during the peak rush while adjacent legs experience 20 minute delays.  Traffic on the heaviest leg just overtakes the roundabout making it difficult for traffic on other legs to enter (especially tractor trailers).


20 minute delays?  That's kinda doubtful there.
Title: Re: Crash prone 'modern roundabouts'
Post by: DaBigE on June 30, 2015, 10:48:15 AM
An example of a how a dominant leg at a roundabout can make it difficult for traffic at other legs to enter the roundabout (especially for semi's).


Looks like the recently reconfigured DePere roundabout (https://www.google.com/maps/@44.4475215,-88.060417,110m/data=!3m1!1e3)
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on June 30, 2015, 11:35:42 AM
Looks like the recently reconfigured DePere roundabout (https://www.google.com/maps/@44.4475215,-88.060417,110m/data=!3m1!1e3)

Thanks DaBigE.  I was wondering what roundabout that was.  Here is a list of roundabouts that have been reconfigured to reduce the number of circulating lanes inside the roundabout.  In every case, reducing the number of circulating lanes was meant to counteract the high crash rates that were occurring at these roundabouts. 

-14th Street & Superior in Lincoln, Nebraska
-Maple & Drake in Farmington Hills, Michigan
-Maple & Farmington in Farmington Hills, Michigan
-Homer Watson Boulevard and Block Line Road in Kitchener, Ontario
-Bailey & Radio in Woodbury, Minnesota
-Broadway Avenue & Lake Street in Forrest Lake, Minnesota
-Main Ave & Broadway in De Pere, Wisconsin
Title: Re: Crash prone 'modern roundabouts'
Post by: DaBigE on June 30, 2015, 12:11:13 PM
Looks like the recently reconfigured DePere roundabout (https://www.google.com/maps/@44.4475215,-88.060417,110m/data=!3m1!1e3)

Thanks DaBigE.  I was wondering what roundabout that was.  Here is a list of roundabouts that have been reconfigured to reduce the number of circulating lanes inside the roundabout.  In every case, reducing the number of circulating lanes was meant to counteract the high crash rates that were occurring at these roundabouts. 

-14th Street & Superior in Lincoln, Nebraska
-Maple & Drake in Farmington Hills, Michigan
-Maple & Farmington in Farmington Hills, Michigan
-Homer Watson Boulevard and Block Line Road in Kitchener, Ontario
-Bailey & Radio in Woodbury, Minnesota
-Broadway Avenue & Lake Street in Forrest Lake, Minnesota
-Main Ave & Broadway in De Pere, Wisconsin

In the case of the DePere roundabout, it wasn't just reducing the circulating lanes. Some of the approach lane assignments were changed as well. WisDOT used to have a nice press release depicting the lane reconfiguration, but since their site was redesigned, I cannot seem to locate it anymore. According to the original plans I found, when the roundabout was first built, the configuration was a symmetrical 2-lane approach for all legs.
Title: Re: Crash prone 'modern roundabouts'
Post by: UCFKnights on June 30, 2015, 10:30:47 PM
I feel multilane roundabout turn indicators seem to not be understood by people for some reason. I was just traveling through Melbourne and had to stop short this weekend for a person turning left from the right lane at this one: https://www.google.com/maps/place/Melbourne,+FL/@28.2298461,-80.725248,126m/data=!3m1!1e3!4m2!3m1!1s0x88de0e2c4771994d:0x8bcdb254a90cd2a8!6m1!1e1

The roundabout seemed to have standard lane markings and then was switched to roundabout turn markings. Actually, on the history street view, it looks like it originally was operating with no road markings or signs of what the lanes do. I am curious which performed better.

The markings in these multilane roundabouts need massive improvement. Our other intersections usually have the lane markings repeated at least 3 times coming up the intersection (where without them, I doubt there would be confusion on most normal intersections). Why not do the same on roundabouts? If a lane only permits one movement, it should have ONLY.  If its a spiral where you're supposed to switch lanes within the roundabout after an exit, we should have extended arrow showing both lanes you can switch to like I've recently seen on Orlando's highways: https://www.google.com/maps/@28.547379,-81.229906,3a,17.4y,271.83h,89.06t/data=!3m6!1e1!3m4!1so_4q0MjltIChCOxVRShxsg!2e0!7i13312!8i6656!6m1!1e1
Title: Re: Crash prone 'modern roundabouts'
Post by: roadfro on June 30, 2015, 11:04:28 PM
If its a spiral where you're supposed to switch lanes within the roundabout after an exit, we should have extended arrow showing both lanes you can switch to like I've recently seen on Orlando's highways: https://www.google.com/maps/@28.547379,-81.229906,3a,17.4y,271.83h,89.06t/data=!3m6!1e1!3m4!1so_4q0MjltIChCOxVRShxsg!2e0!7i13312!8i6656!6m1!1e1

If it's a spiral, you wouldn't be changing lanes. Rather, the lane markings should naturally guide you to the outside at a specified point. (Of course, this assumes that the markings and roundabout features are properly designed to do this.
Title: Re: Crash prone 'modern roundabouts'
Post by: english si on July 01, 2015, 03:43:15 AM
20 minute delays?  That's kinda doubtful there.
Indeed, but don't get in the way of someone and their pet hate.

Of course the reason this thread exists doesn't seem to be the increased crash rate (mostly caused by diastavrosophobia and people's refusal to yield on entry for a couple of years after installation) but rather the OP's hatred of anything that mucks up his signal procession diagrams - non signallised interchanges, and parclos that aren't type B4.

I used to live in a city that replaced roundabouts with signals at almost every location (having the most in Europe). It had the most state of the art systems controlling them. Some junctions would have 20min delays most peak ones - and oddly not ones between major roads, and there were times when there was total gridlock. My last house move within the city would have been better done with a pack mule than a car, as it occurred on a gridlock day. Speeds were roughly 0.5mph on all the roads - each of the 6 times I travelled from my new house to the city centre or back, it took about 80 or 90 minutes - it's walk-able in 40.
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on July 01, 2015, 04:05:34 AM
If its a spiral where you're supposed to switch lanes within the roundabout after an exit, we should have extended arrow showing both lanes you can switch to like I've recently seen on Orlando's highways: https://www.google.com/maps/@28.547379,-81.229906,3a,17.4y,271.83h,89.06t/data=!3m6!1e1!3m4!1so_4q0MjltIChCOxVRShxsg!2e0!7i13312!8i6656!6m1!1e1

That style of arrow is very British. I've never seen such an arrow in the US before.
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on July 01, 2015, 09:27:14 AM
If its a spiral where you're supposed to switch lanes within the roundabout after an exit, we should have extended arrow showing both lanes you can switch to like I've recently seen on Orlando's highways: https://www.google.com/maps/@28.547379,-81.229906,3a,17.4y,271.83h,89.06t/data=!3m6!1e1!3m4!1so_4q0MjltIChCOxVRShxsg!2e0!7i13312!8i6656!6m1!1e1

That style of arrow is very British. I've never seen such an arrow in the US before.

In the aerial view, it's a shame there's a truck driving over the arrow at the time. But you can see the advanced painted arrows are the traditional MUTCD arrows, then the very elongated British-looking arrow.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 01, 2015, 10:57:53 AM
20 minute delays?  That's kinda doubtful there.
Indeed, but don't get in the way of someone and their pet hate.

Of course the reason this thread exists doesn't seem to be the increased crash rate (mostly caused by diastavrosophobia and people's refusal to yield on entry for a couple of years after installation) but rather the OP's hatred of anything that mucks up his signal procession diagrams - non signallised interchanges, and parclos that aren't type B4.

I used to live in a city that replaced roundabouts with signals at almost every location (having the most in Europe). It had the most state of the art systems controlling them. Some junctions would have 20min delays most peak ones - and oddly not ones between major roads, and there were times when there was total gridlock. My last house move within the city would have been better done with a pack mule than a car, as it occurred on a gridlock day. Speeds were roughly 0.5mph on all the roads - each of the 6 times I travelled from my new house to the city centre or back, it took about 80 or 90 minutes - it's walk-able in 40.

I'm in favor of roundabouts.  This thread highlights 2x2 and 3x2 roundabouts have seen an increase in total crashes AND suggests solutions to reduce the crash rates at these high volume roundabouts.  If i had such a hatred for roundabouts, why would i be so interested in how central island diameters impact crash rates?

Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 01, 2015, 03:38:49 PM
Here are back-to-back-to-back 3-lane roundabouts in Green Bay Wisconsin (all spirals  :clap:).  Looking at the crash data from Shawano Avenue & Taylor Street it seems to be performing pretty well (only 30 crashes from 2010-2012... roundabout was constructed in 2011).

https://www.google.com/maps/@44.5369,-88.07445,1247m/data=!3m1!1e3

2010-2012 Green Bay Metropolitan Area Intersection Crash Study
http://www.co.brown.wi.us/i/f/Metro%20area%20crash%20study%20for%202010-2012%20%28final%29%20-%20February%202015.pdf
Title: Re: Crash prone 'modern roundabouts'
Post by: UCFKnights on July 01, 2015, 06:08:43 PM
If its a spiral where you're supposed to switch lanes within the roundabout after an exit, we should have extended arrow showing both lanes you can switch to like I've recently seen on Orlando's highways: https://www.google.com/maps/@28.547379,-81.229906,3a,17.4y,271.83h,89.06t/data=!3m6!1e1!3m4!1so_4q0MjltIChCOxVRShxsg!2e0!7i13312!8i6656!6m1!1e1

That style of arrow is very British. I've never seen such an arrow in the US before.

In the aerial view, it's a shame there's a truck driving over the arrow at the time. But you can see the advanced painted arrows are the traditional MUTCD arrows, then the very elongated British-looking arrow.
They are all over Orlando's highways now wherever they have the lanes with 2 choices. However, they were added relatively recently, post-satellite view updates.
Title: Re: Crash prone 'modern roundabouts'
Post by: johndoe on July 02, 2015, 02:06:56 PM
The roundabout seemed to have standard lane markings and then was switched to roundabout turn markings. Actually, on the history street view, it looks like it originally was operating with no road markings or signs of what the lanes do. I am curious which performed better.

If memory serves some agencies are going AWAY from "fishhook" (roundabout specific) arrow markings because they are believed to be more complicated than necessary.  They're going back to the traditional arrows.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 06, 2015, 12:50:04 PM
The roundabout seemed to have standard lane markings and then was switched to roundabout turn markings. Actually, on the history street view, it looks like it originally was operating with no road markings or signs of what the lanes do. I am curious which performed better.

If memory serves some agencies are going AWAY from "fishhook" (roundabout specific) arrow markings because they are believed to be more complicated than necessary.  They're going back to the traditional arrows.

The study done on the Richfield, Minnesota roundabout at 66th & Portland (previously discussed in this thread) did suggest that the standard arrows are less confusing to drivers than the fishhooks.  That said the roundabout was recently repainted with fishhook pavement markings (well after the release of the study).

The Richfield roundabout is a 2x2 non-spiral roundabout with a central island diameter of 95 feet and an AADT of 29,000 vehicles.  The Richfield roundabout has the characteristics of other accident prone roundabouts cited on this thread.  Tweaking pavement markings and signage isn’t going to increase the central island diameter of the roundabout from 95 feet to 150 feet.
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on July 06, 2015, 06:08:55 PM
Tweaking pavement markings and signage isn’t going to increase the central island diameter of the roundabout from 95 feet to 150 feet.

So the only way to make a roundabout safer is to make it larger? I find that very hard to believe. Despite all these stats, I haven't seen any studies on turbo roundabouts (Dutch-style), which are relatively tiny but seem to have characteristics of what I would think a safe roundabout would at least look like.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 07, 2015, 02:42:11 AM
So the only way to make a roundabout safer is to make it larger? I find that very hard to believe.

The point I was making is there may be a fundamental problem with these crash prone roundabouts that can’t be fixed with pavement marking tweaks.  This thread has compared the safety of spiral vs. non-spiral roundabouts, interchange vs. non-interchange roundabouts, the effects of reducing the number of circulating lanes (converting 2x2 roundabouts to 2x1 roundabouts), and discussed how faded pavement markings can lead to driver error (specifically faded spiral markings).  Other topics in regards to safety include entry angles, overhead signage, fishhook vs standard markings, etc, etc.   You are basically ignoring the entire thread when you make that implication.

Despite all these stats, I haven't seen any studies on turbo roundabouts (Dutch-style),

Literature exists in regards to the safety performance of turbo-roundabouts:
http://trrjournalonline.trb.org/doi/10.3141/2096-03

which are relatively tiny

This turbo roundabout isn’t tiny:
https://www.google.com/maps/@51.9680282,4.4556574,121m/data=!3m1!1e3

but seem to have characteristics of what I would think a safe roundabout would at least look like.

Actual crash data is useful in verifying that preconceived notion.
Title: Re: Crash prone 'modern roundabouts'
Post by: DaBigE on July 07, 2015, 01:31:05 PM
...a fundamental problem with these crash prone roundabouts that can’t be fixed...

In many cases, that problem is the self-centered driver. The ones in a hurry, distracted, and like to make their own traffic rules. You can't just look at the sheer number of crashes alone. You have to look at the type/cause of crash, and the majority of the time it's been due to failure to yield or improper lane usage. If there was a way to accurately track near-misses, I bet the larger roundabouts aren't any better.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 07, 2015, 03:49:49 PM
...a fundamental problem with these crash prone roundabouts that can’t be fixed...

In many cases, that problem is the self-centered driver. The ones in a hurry, distracted, and like to make their own traffic rules. You can't just look at the sheer number of crashes alone. You have to look at the type/cause of crash, and the majority of the time it's been due to failure to yield or improper lane usage. If there was a way to accurately track near-misses, I bet the larger roundabouts aren't any better.

The majority of crashes at signalized intersections are due to driver error.
The majority of crashes at modern roundabouts are due to driver error. 

The very first post in this thread has a link to SEMCOG crash data for the roundabout at State & Ellsworth in Ann Arbor.  Most of the crashes were due to failure to yield (angle) and improper lane usage (sideswipe same).  The 3 years before the roundabout, the intersection averaged 18 crashes a year.  The first year after the roundabout, there were 170 crashes.  Can the roundabout at State & Ellsworth be considered a success because the majority of the 170 crashes was due to driver error?  I don't think so.

Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 07, 2015, 05:29:08 PM
Larger roundabouts may be safer assuming the entry angles of the roundabout are designed properly and circulating speeds remain low.  Consider the following scenario.  CAR A enters the roundabout mistakenly believing CAR B is about to exit.  Would u want CAR B to take 1.7 seconds or 3.4 seconds to travel the blue path?  More reaction time is a good thing!

95 FT central island diameter:
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Test4_zpshnyyiesp.jpg)

160 FT central island diameter:
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Test3_zpscdfdzp4h.jpg)
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on July 07, 2015, 05:31:47 PM
Consider the following scenario.  CAR A enters the roundabout mistakenly believing CAR B is about to exit.  Would u want CAR B to take 1.7 seconds or 3.4 seconds to travel the blue path?  More reaction time is a good thing!

This is probably the best reasoning I've heard in a long time. That actually makes quite a lot of sense.
Title: Re: Crash prone 'modern roundabouts'
Post by: iBallasticwolf2 on July 07, 2015, 05:34:06 PM
Consider the following scenario.  CAR A enters the roundabout mistakenly believing CAR B is about to exit.  Would u want CAR B to take 1.7 seconds or 3.4 seconds to travel the blue path?  More reaction time is a good thing!

This is probably the best reasoning I've heard in a long time. That actually makes quite a lot of sense.

This determines that a larger diameter in a roundabout might be a good thing.
Title: Re: Crash prone 'modern roundabouts'
Post by: DaBigE on July 07, 2015, 05:59:22 PM
Larger roundabouts may be safer assuming the entry angles of the roundabout are designed properly and circulating speeds remain low.  Consider the following scenario.  CAR A enters the roundabout mistakenly believing CAR B is about to exit.  Would u want CAR B to take 1.7 seconds or 3.4 seconds to travel the blue path?  More reaction time is a good thing!

95 FT central island diameter:
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Test4_zpshnyyiesp.jpg)

160 FT central island diameter:
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Test3_zpscdfdzp4h.jpg)

You make the assumption that vehicle B will be traveling the same speed in both scenarios. The larger the circle, the faster vehicle B can comfortably travel. The faster vehicle B is traveling, the harder it is for vehicle A to judge the gap.
Title: Re: Crash prone 'modern roundabouts'
Post by: DaBigE on July 07, 2015, 06:25:10 PM
...a fundamental problem with these crash prone roundabouts that can’t be fixed...

In many cases, that problem is the self-centered driver. The ones in a hurry, distracted, and like to make their own traffic rules. You can't just look at the sheer number of crashes alone. You have to look at the type/cause of crash, and the majority of the time it's been due to failure to yield or improper lane usage. If there was a way to accurately track near-misses, I bet the larger roundabouts aren't any better.

The majority of crashes at signalized intersections are due to driver error.
The majority of crashes at modern roundabouts are due to driver error. 

The very first post in this thread has a link to SEMCOG crash data for the roundabout at State & Ellsworth in Ann Arbor.  Most of the crashes were due to failure to yield (angle) and improper lane usage (sideswipe same).  The 3 years before the roundabout, the intersection averaged 18 crashes a year.  The first year after the roundabout, there were 170 crashes.  Can the roundabout at State & Ellsworth be considered a success because the majority of the 170 crashes was due to driver error?  I don't think so.

You missed the point entirely. Where is there claim that either was a success? In reducing/eliminating fatalities, maybe. Back to the point I was trying to make...Increases in education and enforcement may be the better solution in many modern roundabout cases. You seem to hang your hat solely on the size hypothesis. Size of the roundabout will not solve the overly aggressive driver nor the ill-informed. All it does is give them more room to screw up and potentially at a higher speed.

Secondly, design philosophies are continually evolving with modern roundabouts. As you have even noted, spiral designs have changed in the past 5-10 years, as have theories on radial vs. offset approach design and limiting sight on the approach. Subtle geometric modifications can have a big impact on how a roundabout operates, without necessarily changing the ICD. Am I saying all roundabouts have an appropriate ICD? No. Some are undersized, others are oversized. Some are victim to poor initial design (fast-path speeds, entry radii, etc.), others are victim to not having the design knowledge we have today. Many are victim to the site's constraints. There is no one-size-fits-all solution. Bigger/smaller isn't always better.
Title: Re: Crash prone 'modern roundabouts'
Post by: iBallasticwolf2 on July 07, 2015, 06:39:11 PM
Larger roundabouts may be safer assuming the entry angles of the roundabout are designed properly and circulating speeds remain low.  Consider the following scenario.  CAR A enters the roundabout mistakenly believing CAR B is about to exit.  Would u want CAR B to take 1.7 seconds or 3.4 seconds to travel the blue path?  More reaction time is a good thing!

95 FT central island diameter:
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Test4_zpshnyyiesp.jpg)

160 FT central island diameter:
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Test3_zpscdfdzp4h.jpg)

You make the assumption that vehicle B will be traveling the same speed in both scenarios. The larger the circle, the faster vehicle B can comfortably travel. The faster vehicle B is traveling, the harder it is for vehicle A to judge the gap.

In that case the speed limit on the roundabout would have to be strictly enforced to make sure the drivers don't go faster. So post speed limit signs all over the roundabout.
Also inform drivers better. Alot of drivers are aggressive or ill-informed. There should be very good guidance for what drivers are supposed to do in a roundabout.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 08, 2015, 10:40:53 AM
You make the assumption that vehicle B will be traveling the same speed in both scenarios. The larger the circle, the faster vehicle B can comfortably travel. The faster vehicle B is traveling, the harder it is for vehicle A to judge the gap.
The circulating speed of the 160 ft diameter roundabout would have to be twice as fast as the circulating speed of the 95 ft diameter roundabout before the gap time would be equal.  The reality is drivers aren’t traveling twice as fast in the 160 ft diameter roundabout.  Don’t ignore the benefits larger diameters may have just because the circulating speeds might be 2-3 mph faster.

Back to the point I was trying to make...Increases in education and enforcement may be the better solution in many modern roundabout cases. You seem to hang your hat solely on the size hypothesis. Size of the roundabout will not solve the overly aggressive driver nor the ill-informed. All it does is give them more room to screw up and potentially at a higher speed.
Aggressive, ill-informed drivers are present at both large and small diameter roundabouts.  Improved driver education is great, but it doesn’t change the fact that smaller diameter roundabouts, based on the crash data, are more accident prone than larger ones.

Secondly, design philosophies are continually evolving with modern roundabouts. As you have even noted, spiral designs have changed in the past 5-10 years, as have theories on radial vs. offset approach design and limiting sight on the approach. Subtle geometric modifications can have a big impact on how a roundabout operates, without necessarily changing the ICD. Am I saying all roundabouts have an appropriate ICD? No. Some are undersized, others are oversized. Some are victim to poor initial design (fast-path speeds, entry radii, etc.), others are victim to not having the design knowledge we have today. Many are victim to the site's constraints. There is no one-size-fits-all solution. Bigger/smaller isn't always better.
Crash data is a good indicator to what design elements are working and which ones could be improved.  I’m sure there are ways to improve the crash rate of roundabouts with small ICD’s and designers have had two decades to tweak them.  Ultimately, the lessons learned at these crash prone roundabouts with small ICDs can be applied to the larger roundabouts to make them as safe as possible.  Size isn’t the only factor to look at, but it does appear to be a key factor.

The fact is State & Ellsworth is a roundabout with a 100 ft central island diameter and had 170 crashes the first year of operation.  What’s the fix?  Other larger diameter roundabouts in SE Michigan didn't see anywhere close to that number of crashes the first year of operation.  Can you really just put the bulk of the blame on ill-informed drivers?  Maybe, just maybe, it's too small.
Title: Re: Crash prone 'modern roundabouts'
Post by: DaBigE on July 08, 2015, 11:08:56 AM
You make the assumption that vehicle B will be traveling the same speed in both scenarios. The larger the circle, the faster vehicle B can comfortably travel. The faster vehicle B is traveling, the harder it is for vehicle A to judge the gap.
The circulating speed of the 160 ft diameter roundabout would have to be twice as fast as the circulating speed of the 95 ft diameter roundabout before the gap time would be equal.  The reality is drivers aren’t traveling twice as fast in the 160 ft diameter roundabout.  Don’t ignore the benefits larger diameters may have just because the circulating speeds might be 2-3 mph faster.
I'm not ignoring the possible benefits; I am trying to look at this issue objectively from all sides.

Size isn’t the only factor to look at, but it does appear to be a key factor.
Something I can agree with, although being a key factor is a matter of semantics. Until the sight to the left on entry, circulating sight, entry radii, and fastest-paths (among other design considerations) are also compared and analyzed for the problematic roundabouts, the ICD is still just a plausible theory. There are many small ICD multilane roundabouts that have not had the PDO-crash growth that some of the ones mentioned in this thread have.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 08, 2015, 12:01:36 PM
There are many small ICD multilane roundabouts that have not had the PDO-crash growth that some of the ones mentioned in this thread have.
There really aren’t that many 2x2 roundabouts that haven’t been mentioned in this thread.  I attempted to query out the major 2x2 roundabouts in America and looked up crash data for as many as I could (found crash data for 14 of 40).  The best performing roundabout with a central island diameter of 100 feet or less still had a 300% increase in crashes.

There was a 300%-1400% increase in crashes at roundabouts with central island diameters of 100 feet or less.  There was a 36%-318% increase in crashes at roundabouts with central island diameters between 120 and 170 feet.  The worst performing large diameter roundabout was almost as good as the best performing small diameter roundabout.

Sure, you may be able to find an aesthetic 2x2 roundabout in a subdivision that hasn't seen an increase in crashes, but that really isn't the focus.  If you have crash data on major 2x2 roundabouts that I don’t, by all means share it with the rest of us. 

Here is a list of 40 multi-lane roundabouts that I think could be meaningful to this conversation.  This was queried from a database of over 5,100 modern roundabouts.  This was the criteria used to query out the list:

-roundabouts constructed within the last 10 years
-all approaches have 2 entry lanes
-roundabouts have 4-legs
-main & side streets are major state or county routes (ie. likely high AADT roundabouts)
-interchange roundabouts (and frontage road roundabouts) not included

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/RBtest_zpsbkjmf4ri.png)

Now the hard part is finding accurate before/after crash data to make any type of analysis.  Here is a google KMZ file that includes the 40 roundabouts in the chart above:

http://www.mediafire.com/download/cd570rarros2c3g/Multi-Lane+Roundabouts+%28with+high+AADT%29.kmz

In a previous post, I queried out 40 multi-lane roundabouts that have 2-entry lanes for all 4-legs (ie. the roundabouts in America that likely have the highest traffic volumes).  I’ve tracked down before/after crash data for 14 of them.  The excel file includes data links to articles/publications where the data was obtained.

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/RBDATASummary_zpsg7upbybr.png)
http://www.mediafire.com/view/p0u5ovrupr0175m/Multi-lane_roundabout_crashes.xlsx

The takeaway is that smaller roundabouts seem to be more accident prone than larger roundabouts.  Would there have been 171 crashes at State & Ellsworth if the roundabout was constructed with a central island diameter of 140’ as opposed to 100’?  This thread wasn't meant to bash roundabouts but to discuss ways to reduce the crash frequency at the highest AADT roundabouts.  My thought is make them just a little bit bigger.
Title: Re: Crash prone 'modern roundabouts'
Post by: Rothman on July 08, 2015, 12:13:40 PM
Are the 3-2-1, 1-2-3 columns years before and after?
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 08, 2015, 12:35:08 PM
Are the 3-2-1, 1-2-3 columns years before and after?

Yes.  3-2-1 represents 3 years before, 2 years before, 1 year before.  1-2-3 represents 1 year after, 2 years after, 3 years after.  The year of construction is not included.  The cells highlighted in grey are average crashes over multiple years.  If you open the excel file it provides links where the crash data was obtained.

http://www.mediafire.com/view/p0u5ovrupr0175m/Multi-lane_roundabout_crashes.xlsx
Title: Re: Crash prone 'modern roundabouts'
Post by: Rothman on July 08, 2015, 01:10:58 PM
Interesting that the crashes for the New Scotland/NY 85/NY 140 roundabout are only one year before and after.  As I've said before, the most mindboggling thing for me going through there are the people that think they can continue to go around the roundabout in the right lane and don't look when they essentially turn left to do so.  I'd bet that kind of thing accounts for a lot of the crashes in the year after the roundabout was built.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 08, 2015, 01:56:55 PM
Interesting that the crashes for the New Scotland/NY 85/NY 140 roundabout are only one year before and after.  As I've said before, the most mindboggling thing more me going through there are the people that think they can continue to go around the roundabout in the right lane and don't look when they essentially turn left to do so.  I'd bet that kind of thing accounts for a lot of the crashes in the year after the roundabout was built.

The roundabout at New Scotland/NY 85/NY 140 is one of the worst performing roundabouts that has a central island diameter between 120-170 feet.  The faded spiral markings could definitely be a contributing factor to the high crash rate seen at this roundabout and has been discussed previously in this thread (the smaller diameter roundabout in Malta, NY also has painted spiral markings).  By the way, I believe the crash data is average crashes over multiple years but the article (linked in the excel file) misrepresented the data to be from only one year before and after. 

Bethlehem, NY (New Scotland Road and Route 140)
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/NYRB_zpsmnpyxdmi.png)

Malta, NY (Route 9, Route 67 and Dunning Street)
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/NYRBMalta_zpsifwwmbgh.png)
Title: Re: Crash prone 'modern roundabouts'
Post by: DaBigE on July 08, 2015, 02:18:43 PM
There are many small ICD multilane roundabouts that have not had the PDO-crash growth that some of the ones mentioned in this thread have.
There really aren’t that many 2x2 roundabouts that haven’t been mentioned in this thread.  I attempted to query out the major 2x2 roundabouts in America and looked up crash data for as many as I could (found crash data for 14 of 40).
Forty? That's it? You're being to limited in your search and you indirectly admit that you don't have enough accurate crash data for all the ones you do list.

Sure, you may be able to find an aesthetic 2x2 roundabout in a subdivision that hasn't seen an increase in crashes.
There is no such thing. You don't build a multilane roundabout just because it looks pretty.

Here is a list of 40 multi-lane roundabouts that I think could be meaningful to this conversation.  This was queried from a database of over 5,100 modern roundabouts.  This was the criteria used to query out the list:

-roundabouts constructed within the last 10 years    Reasonable
-all approaches have 2 entry lanes    Why exclude roundabouts that may have one or two legs with a single lane entry?
-roundabouts have 4-legs    Exactly 4 or >=4? Why exclude 3-leg 2x2 roundabouts?
-main & side streets are major state or county routes (ie. likely high AADT roundabouts)    Not an accurate assumption...while likely, there still are a number that are solely local arterial roads, and not numbered/lettered routes. Ex: Thompson/Lein/Zeier, Madison (https://www.google.com/maps/@43.121535,-89.299519,18z), Thompson/Main, Sun Prairie (https://www.google.com/maps/@43.1764051,-89.254479,19z)
-interchange roundabouts (and frontage road roundabouts) not included    Why? Just because interchange roundabouts don't have 4 complete approaches?
As I said above, you're being too limiting in your search. Some might say you're cherry-picking data. The lack of complete crash data skews the whole process. I could list many multilane roundabouts that you haven't mentioned, but they would/should get thrown-out because the intersection did not exist before the roundabout, thus there is no before period to compare to.

This is going in nothing but circles (pun not intended). I tried to find common ground in your reasonable query on roundabout size, but you are blinded into focusing solely on size. Is size a factor? Yes. Does it deserve more scientifically-acceptable research? Most certainly. Is it the only factor where crashes are a problem? No. Roundabout design isn't that simplistic. You started a discussion on "crash-prone 'modern roundabouts'", when a more accurate subject would be 'why modern roundabouts are too small'.
Title: Re: Crash prone 'modern roundabouts'
Post by: Rothman on July 08, 2015, 02:27:53 PM
I drive through that roundabout a couple of times a week and can say with certainty that crashes are not due to faded pavement markings.  The thing is still well-marked and even signed.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 08, 2015, 03:04:27 PM
I drive through that roundabout a couple of times a week and can say with certainty that crashes are not due to faded pavement markings.  The thing is still well-marked and even signed.

Even with perfectly visible pavement markings, drivers are going to cheat.  The driver in the blue SUV is asking themselves "is the silver Honda in the outside or inside lane?"  Let's hope they don't guess wrong. 

Hell, i'd encourage you to take video of the Bethlehem roundabout and post it online so we can see for ourselves if improper lane use is a problem at this roundabout.  It wouldn't be that hard to do.

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/SVMalta_zpspdoii1ub.png)
Title: Re: Crash prone 'modern roundabouts'
Post by: Rothman on July 08, 2015, 03:07:38 PM
Heh.  Like I said, the crashes in the 1st year afterwards are probably due to people turning left from the right lane and I'd bet the frequency of lane misuse has dropped -- although I still witness it from time-to-time.

Might make that video when I get a chance.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 08, 2015, 03:29:03 PM
Heh.  Like I said, the crashes in the 1st year afterwards are probably due to people turning left from the right lane and I'd bet the frequency of lane misuse has dropped -- although I still witness it from time-to-time.

Might make that video when I get a chance.

Here’s the next best thing to a video.  Here are streetview images tracking a vehicle through the roundabout in Malta, NY (which has an identical spiral design to the roundabout in Bethlehem NY).  At some point the blue SUV may think it’s safe to enter the roundabout (since the silver Honda is in the inside left turn only lane).
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Test1_zps4crezouf.jpg)
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Test2_zpszpwpcomn.jpg)
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Test3_zps2kf2y7bb.jpg)
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Test4_zpsmeqbau38.jpg)
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/test5_zpsifja6ucx.jpg)
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/test6_zpslnjnyuzg.jpg)

The silver Honda is cheating their way through the roundabout.

Title: Re: Crash prone 'modern roundabouts'
Post by: lordsutch on July 08, 2015, 04:22:46 PM
Most of the crashes were in year one... the year the pavement markings almost certainly weren't faded. Hence faded lines don't, and can't, explain jack.

As for the silver Honda... dude is like 1 foot across the line for maybe 20 feet without endangering any other traffic. People drift across lane lines all the time. Give it a rest.

Free advice from one data scientist: stop torturing the data to fit an agenda.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 08, 2015, 06:02:15 PM
Most of the crashes were in year one... the year the pavement markings almost certainly weren't faded. Hence faded lines don't, and can't, explain jack.

I don't have year by year crash data for the NY roundabout.  How do u know that the majority of crashes happened in year one?

As for the silver Honda... dude is like 1 foot across the line for maybe 20 feet without endangering any other traffic. People drift across lane lines all the time. Give it a rest.

Dude is entirely in the inner lane in the 3rd picture.  I only had streetview (not many examples to pick from) so sorry if i couldn't find a better example of the scenario

Free advice from one data scientist: stop torturing the data to fit an agenda.

I'm just looking for trends.  The crash data shows that there are fewer crashes at larger diameter roundabouts.  Therefore, I'm in favor of larger roundabouts.  If the data had shown that there are fewer crashes at smaller diameter roundabouts, then i would be in favor of smaller diameter roundabouts.
Title: Re: Crash prone 'modern roundabouts'
Post by: Rothman on July 08, 2015, 07:24:27 PM
Most of the crashes were in year one... the year the pavement markings almost certainly weren't faded. Hence faded lines don't, and can't, explain jack.

I don't have year by year crash data for the NY roundabout.  How do u know that the majority of crashes happened in year one?


Eh...your percentage increases treats them as if you did have year-to-year.  Can't have it both ways.
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on July 08, 2015, 07:26:16 PM
The crash data shows that there are fewer crashes at larger diameter roundabouts.  Therefore, I'm in favor of larger roundabouts.  If the data had shown that there are fewer crashes at smaller diameter roundabouts, then i would be in favor of smaller diameter roundabouts.

But the data is only representative of the few roundabouts you can find data for. I don't think making such large generalizations is a good idea without a significant amount of data.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 08, 2015, 07:53:01 PM
Most of the crashes were in year one... the year the pavement markings almost certainly weren't faded. Hence faded lines don't, and can't, explain jack.

I don't have year by year crash data for the NY roundabout.  How do u know that the majority of crashes happened in year one?


Eh...your percentage increases treats them as if you did have year-to-year.  Can't have it both ways.

Cells highlighted in grey are average crashes over multiple years.  The before and after crash data cells for the Bethlehem, NY and Malta, NY roundabouts are highlighted in grey.  I'm not trying to fool anyone.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 08, 2015, 08:25:47 PM
The crash data shows that there are fewer crashes at larger diameter roundabouts.  Therefore, I'm in favor of larger roundabouts.  If the data had shown that there are fewer crashes at smaller diameter roundabouts, then i would be in favor of smaller diameter roundabouts.

But the data is only representative of the few roundabouts you can find data for. I don't think making such large generalizations is a good idea without a significant amount of data.

The Insurance Institute for Highway Safety study only evaluated 9 multi-lane roundabouts.  This 15 year old study is routinely cited in roundabout articles and is the go to source when it comes to roundabout safety statistics.  I’m evaluating the safety performance of 14 multi-lane roundabouts.  The amount of data being evaluated is not insignificant.
Title: Re: Crash prone 'modern roundabouts'
Post by: Rothman on July 08, 2015, 09:08:15 PM
Most of the crashes were in year one... the year the pavement markings almost certainly weren't faded. Hence faded lines don't, and can't, explain jack.

I don't have year by year crash data for the NY roundabout.  How do u know that the majority of crashes happened in year one?


Eh...your percentage increases treats them as if you did have year-to-year.  Can't have it both ways.

Cells highlighted in grey are average crashes over multiple years.

I'm going to have call baloney on this repeated assertion as well regarding the New Scotland roundabout.  You're saying that the average in the first three years was 9.6 per year and then the average in the three years afterwards was 38.3. per year.

That's total baloney.  In essence, you're saying that there was at least one incident in the roundabout every 10 days for three years after it was built. I highly suspect that you have warped the data into something for which it was not intended.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 08, 2015, 09:40:36 PM
I'm going to have call baloney on this repeated assertion as well regarding the New Scotland roundabout.  You're saying that the average in the first three years was 9.6 per year and then the average in the three years afterwards was 38.3. per year.

That's total baloney.  In essence, you're saying that there was at least one incident in the roundabout every 10 days for three years after it was built. I highly suspect that you have warped the data into something for which it was not intended.


I don't understand what is so hard to believe.  Does 38 crashes a year sound too high to you?  To put it into perspective, there are over 50 intersections in SE Michigan that have averaged at least 38 crashes a year.

http://semcog.org/Data-and-Maps/High-Frequency-Crash-Locations

Title: Re: Crash prone 'modern roundabouts'
Post by: roadfro on July 08, 2015, 10:22:16 PM
Here is a list of 40 multi-lane roundabouts that I think could be meaningful to this conversation.  This was queried from a database of over 5,100 modern roundabouts.  This was the criteria used to query out the list:

-roundabouts constructed within the last 10 years    Reasonable
-all approaches have 2 entry lanes    Why exclude roundabouts that may have one or two legs with a single lane entry?
-roundabouts have 4-legs    Exactly 4 or >=4? Why exclude 3-leg 2x2 roundabouts?
-main & side streets are major state or county routes (ie. likely high AADT roundabouts)    Not an accurate assumption...while likely, there still are a number that are solely local arterial roads, and not numbered/lettered routes. Ex: Thompson/Lein/Zeier, Madison (https://www.google.com/maps/@43.121535,-89.299519,18z), Thompson/Main, Sun Prairie (https://www.google.com/maps/@43.1764051,-89.254479,19z)
-interchange roundabouts (and frontage road roundabouts) not included    Why? Just because interchange roundabouts don't have 4 complete approaches?
As I said above, you're being too limiting in your search. Some might say you're cherry-picking data. The lack of complete crash data skews the whole process. I could list many multilane roundabouts that you haven't mentioned, but they would/should get thrown-out because the intersection did not exist before the roundabout, thus there is no before period to compare to.

This is going in nothing but circles (pun not intended). I tried to find common ground in your reasonable query on roundabout size, but you are blinded into focusing solely on size. Is size a factor? Yes. Does it deserve more scientifically-acceptable research? Most certainly. Is it the only factor where crashes are a problem? No. Roundabout design isn't that simplistic. You started a discussion on "crash-prone 'modern roundabouts'", when a more accurate subject would be 'why modern roundabouts are too small'.

DaBigE, I think some of your assumptions about tradephoric's data and filtering criteria are a little unreasonable.

In order to effectively analyze roundabouts from various locations to draw some general conclusions, you have to limit the data in some way in order to have the analysis make sense and reduce effects from other variables. One way to do that is looking for substantially similar conditions at various sites. Limiting the sample to 4-leg roundabouts with double lane approaches on all sides makes valid sense in this data analysis—otherwise, you're not making an "apples to apples" comparison and can not make the same generalizations because other design factors can influence the data. (Although I would agree that the limitation to include just state/county routes isn't necessarily a good one, but I understand the rationale in trying to find roundabouts with similar AADTs. Finding that data in relation to crash data for specific sites might not be an easy endeavor for armchair/hobbyist analysis purposes.)

When you have raw data like this in a tabular format, with similar site characteristics, any good data analysis would attempt to find patterns in said data. Tradephoric found one possible trend between a possible variable (inscribed circle diameter) and accident rates, and has commented on this specifically. I don't think we could say with any reasonable certainty that there is a direct correlation without more analysis, but it is a plausible theory worth further examination (possibly worthy of a civil/traffic engineering journal article). And by no means is ICD the only possible factor influencing the accident rates at these sites—but to examine multiple possible factors independent of others would require much more research and site visits.; however, it is one that is easy to examine without making a detailed site visit.
Title: Re: Crash prone 'modern roundabouts'
Post by: Rothman on July 09, 2015, 12:24:04 AM
I'm going to have call baloney on this repeated assertion as well regarding the New Scotland roundabout.  You're saying that the average in the first three years was 9.6 per year and then the average in the three years afterwards was 38.3. per year.

That's total baloney.  In essence, you're saying that there was at least one incident in the roundabout every 10 days for three years after it was built. I highly suspect that you have warped the data into something for which it was not intended.


I don't understand what is so hard to believe.  Does 38 crashes a year sound too high to you?  To put it into perspective, there are over 50 intersections in SE Michigan that have averaged at least 38 crashes a year.

http://semcog.org/Data-and-Maps/High-Frequency-Crash-Locations



Yep.  38 crashes a year at that roundabout in the three years since it was built does sound far too high.
Title: Re: Crash prone 'modern roundabouts'
Post by: DaBigE on July 09, 2015, 12:29:57 AM
DaBigE, I think some of your assumptions about tradephoric's data and filtering criteria are a little unreasonable.
And I respectfully disagree. The initial discussion was based on multilane roundabouts in general, not specifically 2x2 roundabouts. In the end, we've mainly been discussing entering and exiting crashes, which don't tend to discriminate very much between a 2x2 or a 1x2 roundabout; as long as there is some multilane component, similar vehicular conflicts can and will exist.

I don't think there is anyone here that disagrees that ICD may play a role or that there is a pattern at many multilane roundabouts; what many of us disagree with is making a broad generalization on very limited data. That said, it is definitely worth looking into further, but from a more detailed approach. I think the size discussion has gone about as far as it can on an enthusiast level. The discussion may even be completely moot, as the recommended range of multilane roundabout size is already greater than the 100-ft threshold of this discussion (Exhibit 6-9, NCHRP Report 672). Many of the roundabouts being discussed likely made smaller because of design concessions/site constraints (e.g., costly right-of-way acquisition, some unmovable feature, etc.).

For similar reasons, I also disagree with the IIHS study being promoted any further because, as tradephoric also pointed out, it was done on fewer roundabouts and over 15 years ago. A lot has changed within the past 5 years, let alone 15. Similarly, as I've said earlier, many of us (professional colleagues included), have fundamental issues with the studies WisDOT has carried out as well.

Analyzing roundabouts is not an easy task, whether it's crash data or capacity. There is a lot of disagreement in the design world. This is one reason why I have been harping on the danger of some of the comparisons of older roundabouts that have not been touched since they were first constructed a decade ago. Design philosophies are still evolving, from a forecasting perspective as well. From that point alone, it will be very hard to ever get an apples-to-apples comparison. Throw in different driving characteristics in the various areas of the country and the similarities disappear even faster.

Looking into the future of multilane roundabouts, some new experiments are gaining traction in a few locations in Texas and a couple in Minnesota: non-striped or limited-striping circulatory roadways. This will blur the analysis picture even more.
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on July 09, 2015, 01:11:17 AM
Looking into the future of multilane roundabouts, some new experiments are gaining traction in a few locations in Texas and a couple in Minnesota: non-striped or limited-striping circulatory roadways. This will blur the analysis picture even more.

I quite like this idea. I've always thought that we go overboard with signage and pavement markings. Do you have any links to these roundabouts?
Title: Re: Crash prone 'modern roundabouts'
Post by: DaBigE on July 09, 2015, 01:18:37 AM
Looking into the future of multilane roundabouts, some new experiments are gaining traction in a few locations in Texas and a couple in Minnesota: non-striped or limited-striping circulatory roadways. This will blur the analysis picture even more.

I quite like this idea. I've always thought that we go overboard with signage and pavement markings. Do you have any links to these roundabouts?

Not yet. Most are either still in final planning phases or are just going to construction.
Title: Re: Crash prone 'modern roundabouts'
Post by: lordsutch on July 09, 2015, 10:30:02 AM
Non-striped circulatory roadways are standard in the UK for unsignalized, multilane roundabouts. For what it's worth...
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on July 09, 2015, 10:58:22 AM
Looking into the future of multilane roundabouts, some new experiments are gaining traction in a few locations in Texas and a couple in Minnesota: non-striped or limited-striping circulatory roadways. This will blur the analysis picture even more.

I quite like this idea. I've always thought that we go overboard with signage and pavement markings. Do you have any links to these roundabouts?

Look up nearly any traditional NJ Traffic Circle, and this is what they are.

Yes, people that should stay left drift to the right, and those that should stay further to the right drift left.  Occasionally, someone from the left exits the circle.  Horns honk.  Words are uttered (mostly behind closed windows).  But overall, very few accidents.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 09, 2015, 11:13:26 AM
Looking into the future of multilane roundabouts, some new experiments are gaining traction in a few locations in Texas and a couple in Minnesota: non-striped or limited-striping circulatory roadways. This will blur the analysis picture even more.

I quite like this idea. I've always thought that we go overboard with signage and pavement markings. Do you have any links to these roundabouts?

Look up nearly any traditional NJ Traffic Circle, and this is what they are.

Yes, people that should stay left drift to the right, and those that should stay further to the right drift left.  Occasionally, someone from the left exits the circle.  Horns honk.  Words are uttered (mostly behind closed windows).  But overall, very few accidents.

When a non-striped traffic circle in Augusta, Maine was converted to a modern roundabout, it saw a 60% drop in crashes (the size of the circle remained the same).  I don't think there is any consensus that non-striped roundabouts would be more effective then striped roundabouts.

http://www.pressherald.com/2013/04/17/terms-for-traffic-circles-cause-confusion_2013-04-18/
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 09, 2015, 11:37:08 AM
The initial discussion was based on multilane roundabouts in general, not specifically 2x2 roundabouts.

The initial discussion was regarding crash prone modern roundabouts.  DaBigE, you questioned why I didn’t include interchange roundabouts.  Based on the WisDOT studies it became clear that interchange roundabouts perform better than non-interchange roundabouts.  Nearly every interchange roundabout in the WisDOT studies saw a drop in crash rate.  You’ve made it known that you have fundamental issues with the WisDOT studies, but I doubt the studies were based on fabricated crash data.  The best performing multi-lane roundabouts in SE Michigan also happen to be at interchange roundabouts.  Logically, it makes sense why interchange roundabouts may have a lower crash rate then other multi-lane roundabouts.  Some legs only service entry or exiting traffic and it could be argued the turning movements are more predictable (certain turning movements won’t be that heavy).  In general, interchange roundabouts just don’t appear to be that accident prone.
Title: Re: Crash prone 'modern roundabouts'
Post by: DaBigE on July 09, 2015, 12:20:00 PM
The initial discussion was based on multilane roundabouts in general, not specifically 2x2 roundabouts.

The initial discussion was regarding crash prone modern roundabouts.  DaBigE, you questioned why I didn’t include interchange roundabouts.  Based on the WisDOT studies it became clear that interchange roundabouts perform better than non-interchange roundabouts.  Nearly every interchange roundabout in the WisDOT studies saw a drop in crash rate.  You’ve made it known that you have fundamental issues with the WisDOT studies, but I doubt the studies were based on fabricated crash data.  The best performing multi-lane roundabouts in SE Michigan also happen to be at interchange roundabouts.  Logically, it makes sense why interchange roundabouts may have a lower crash rate then other multi-lane roundabouts.  Some legs only service entry or exiting traffic and it could be argued the turning movements are more predictable (certain turning movements won’t be that heavy).  In general, interchange roundabouts just don’t appear to be that accident prone.

First, no one is claiming that the studies are coming from "fabricated crash data". The studies' flaws had more to do with site selection. Secondly, if you're trying to prove whether size has a significant contributing factor, why throw out roundabouts with lower crash rates? In order to make a generalization such as size being a "key factor", you need to look at all the data, not just the ones that have the best chance of proving your point. Maybe the ones you chose not to include also help prove a larger size theory.
Title: Re: Crash prone 'modern roundabouts'
Post by: DaBigE on July 09, 2015, 12:23:44 PM
Non-striped circulatory roadways are standard in the UK for unsignalized, multilane roundabouts. For what it's worth...

That is one of the reasons why it is being tried in the US, in addition to less striping maintenance. There is a design theory that stripes should be applied to increase capacity rather than to keep people in-lane. Lack of circulatory striping also removes the confusion when a large vehicle is moving through, as there are no lane lines to have to straddle.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 09, 2015, 02:11:06 PM
First, no one is claiming that the studies are coming from "fabricated crash data". The studies' flaws had more to do with site selection.

I was curious what you took issue with regarding the WisDOT studies.  Some roundabout proponents may attempt to discredit any study that shows roundabouts in a negative light.  It feels like there's a little bit of “let’s shoot the messenger” with these WisDOT studies.

Secondly, if you're trying to prove whether size has a significant contributing factor, why throw out roundabouts with lower crash rates? In order to make a generalization such as size being a "key factor", you need to look at all the data, not just the ones that have the best chance of proving your point. Maybe the ones you chose not to include also help prove a larger size theory.

More data is not always useful.  Here are some low volume 2x2 roundabouts that services subdivisions, commercial office complexes, schools, etc.  Would crash data at these roundabouts (which might average 0.6 crashes/year) be useful in this discussion?  It would become an apples to bananas comparison.   
 
https://www.google.com/maps/@39.22989,-77.2528,18z/data=!3m1!1e3
https://www.google.com/maps/@35.84866,-86.35948,365m/data=!3m1!1e3
https://www.google.com/maps/@30.10538,-81.4157,19z/data=!3m1!1e3
https://www.google.com/maps/@38.9684442,-76.9233194,117m/data=!3m1!1e3
https://www.google.com/maps/@38.9383773,-104.734292,98m/data=!3m1!1e3
Title: Re: Crash prone 'modern roundabouts'
Post by: johndoe on July 09, 2015, 08:08:27 PM
... increase the central island diameter of the roundabout from 95 feet to 150 feet.
Sorry if this has been covered...but is there a reason you don't do your analysis based upon the inscribed diameter?  I ask since that's usually how they're usually laid out (in my experience).

Title: Re: Crash prone 'modern roundabouts'
Post by: DaBigE on July 09, 2015, 08:21:11 PM
First, no one is claiming that the studies are coming from "fabricated crash data". The studies' flaws had more to do with site selection.

I was curious what you took issue with regarding the WisDOT studies.  Some roundabout proponents may attempt to discredit any study that shows roundabouts in a negative light.  It feels like there's a little bit of “let’s shoot the messenger” with these WisDOT studies.
And I'm not sensing that same vibe. Sure, there's a few hell-bent on 'roundabouts everywhere' just like there's similar chest-beaters for traffic signals or DDIs. Most in the design community are taking these studies and trying to find why are these crashes happening, not why are these studies wrong. However, we want to work with the most accurate and complete data we can. Most of us don't get paid based on the number of 'xyz' intersection type are constructed.

In the interest of preventing future false assumptions, I am not one of those roundabout proponents, rather I am a proponent of using the proper tool for the proper location. Roundabouts won't work everywhere, nor will traffic signals or cloverleaf interchanges. I'm just as interested in finding out why crashes are higher in some places and not others. That's not to say there aren't earmarked projects, like many HSIP-funded intersection projects.

More data is not always useful.
The only time more data is not useful is if the data is flawed, incorrect, or objectively erroneous data. In any case, bad data should be objectively removed before attempting any formal conclusions. You don't establish reliable trend lines based on only a little data. That is one of the reasons why LOS analysis equations for roundabout capacity prediction are continually being adjusted.

Here are some low volume 2x2 roundabouts that services subdivisions, commercial office complexes, schools, etc.  Would crash data at these roundabouts (which might average 0.6 crashes/year) be useful in this discussion?  It would become an apples to bananas comparison.   
 
https://www.google.com/maps/@39.22989,-77.2528,18z/data=!3m1!1e3
https://www.google.com/maps/@35.84866,-86.35948,365m/data=!3m1!1e3
https://www.google.com/maps/@30.10538,-81.4157,19z/data=!3m1!1e3
https://www.google.com/maps/@38.9684442,-76.9233194,117m/data=!3m1!1e3
https://www.google.com/maps/@38.9383773,-104.734292,98m/data=!3m1!1e3
You answered your own question by saying they are low-volume. Only if an adjustment is made to correct for volume disparities would this data be useful for anything but analyzing low-volume roundabouts. Your original list of qualifications was looking for multilane roundabouts of a certain AADT. All I am saying is that intersections of similar AADTs shouldn't be omitted in this case just because they have a low crash rate (referring to the afore-mentioned interchange or frontage road roundabouts). Maybe their size helps prove a size/crash relationship.

On a somewhat unrelated topic, I do see some poor yield line placement in a few of your latest examples.
Title: Re: Crash prone 'modern roundabouts'
Post by: DaBigE on July 09, 2015, 08:27:32 PM
... increase the central island diameter of the roundabout from 95 feet to 150 feet.
Sorry if this has been covered...but is there a reason you don't do your analysis based upon the inscribed diameter?  I ask since that's usually how they're usually laid out (in my experience).
That is correct. Central island size is generally a byproduct from the ICD and circulatory lane width(s), in addition to possibly allowing for future staged capacity enhancements.
Title: Re: Crash prone 'modern roundabouts'
Post by: lordsutch on July 10, 2015, 12:33:30 AM
All I am saying is that intersections of similar AADTs shouldn't be omitted in this case just because they have a low crash rate (referring to the afore-mentioned interchange or frontage road roundabouts). Maybe their size helps prove a size/crash relationship.

Indeed. This is what is referred to as "selecting on the dependent variable." You can't (validly) conclude that roundabouts of a certain type with a certain AADT or above have a high crash rate if you omit all the roundabouts of the same type and AADT that have zero or low crash rates.

What you could validly do is compare the characteristics of roundabouts that have high crash rates with those with low crash rates (but similar AADT and lane counts) to identify if there are meaningful patterns that distinguish the high-crash ones from low-crash ones (for example, entry angle, striping design, signage, use of traffic calming treatments like rumble stripes, signed speed limits, advisory speed plaques, lighting, landscaping...).
Title: Re: Crash prone 'modern roundabouts'
Post by: ScottRAB on July 10, 2015, 03:50:18 PM
Look up nearly any traditional NJ Traffic Circle, and this is what they are.

not sure if I got the right attribution:
Modern roundabouts are traffic circles, but traffic circles are not modern roundabouts.
   Many people confuse other and older styles of circular intersections with modern roundabouts.  East coast rotaries, large multi-lane traffic circles (Arc D’Triomphe, Dupont Circle), and small neighborhood traffic circles are not modern roundabouts.   If you want to see the difference between a traffic circle, a rotary (UK roundabout) and a modern roundabout (UK continental roundabout), go to http://tinyurl.com/kstate-RAB  to see pictures.   And here’s another site that shows the difference between an older rotary and a modern roundabout: http://tinyurl.com/bzf7qmg
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 14, 2015, 11:35:41 AM
Larger roundabouts may be safer assuming the entry angles of the roundabout are designed properly and circulating speeds remain low.  Consider the following scenario.  CAR A enters the roundabout mistakenly believing CAR B is about to exit.  Would u want CAR B to take 1.7 seconds or 3.4 seconds to travel the blue path?  More reaction time is a good thing!

95 FT central island diameter:
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Test4_zpshnyyiesp.jpg)

160 FT central island diameter:
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Test3_zpscdfdzp4h.jpg)

You make the assumption that vehicle B will be traveling the same speed in both scenarios. The larger the circle, the faster vehicle B can comfortably travel. The faster vehicle B is traveling, the harder it is for vehicle A to judge the gap.

Your general assumption that drivers feel more comfortable driving faster in larger circles is wrong.  The red min-van may feel comfortable traveling through this circle at 90 mph (in a straight line). 

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/B93174221541-0_zpsega85sti.jpg)

Relating specifically to modern-roundabouts, the same type of straight line fastest path can occur.  Here’s an example of a small diameter modern-roundabout in Oconomowoc, Wisconsin where the fastest path through the roundabout is approaching a straight line.  I know it sounds counter-intuitive, but larger diameter roundabout can actually slow down the speeds of circulating traffic.

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/fastestpath_zpskfw1ywq5.jpg)

The 160 ft diameter roundabout had a 48% increase in crashes whereas the 95 ft diameter roundabout had a 335% increase in crashes.  Is it possible that drivers at the 160 ft diameter roundabout can judge gaps in traffic better than the 95 diameter one and that is reflected in the crash data?
Title: Re: Crash prone 'modern roundabouts'
Post by: iBallasticwolf2 on July 14, 2015, 11:40:53 AM
Larger roundabouts may be safer assuming the entry angles of the roundabout are designed properly and circulating speeds remain low.  Consider the following scenario.  CAR A enters the roundabout mistakenly believing CAR B is about to exit.  Would u want CAR B to take 1.7 seconds or 3.4 seconds to travel the blue path?  More reaction time is a good thing!

95 FT central island diameter:
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Test4_zpshnyyiesp.jpg)

160 FT central island diameter:
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Test3_zpscdfdzp4h.jpg)

You make the assumption that vehicle B will be traveling the same speed in both scenarios. The larger the circle, the faster vehicle B can comfortably travel. The faster vehicle B is traveling, the harder it is for vehicle A to judge the gap.

Your general assumption that drivers feel more comfortable driving faster in larger circles is wrong.  The red min-van may feel comfortable traveling through this circle at 90 mph (in a straight line). 

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/B93174221541-0_zpsega85sti.jpg)

Relating specifically to modern-roundabouts, the same type of straight line fastest path can occur.  Here’s an example of a small diameter modern-roundabout in Oconomowoc, Wisconsin where the fastest path through the roundabout is approaching a straight line.  I know it sounds counter-intuitive, but larger diameter roundabout can actually slow down the speeds of circulating traffic.

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/fastestpath_zpskfw1ywq5.jpg)

The 160 ft diameter roundabout had a 48% increase in crashes whereas the 95 ft diameter roundabout had a 335% increase in crashes.  Is it possible that drivers at the 160 ft diameter roundabout can judge gaps in traffic better than the 95 diameter one and that is reflected in the crash data?

Assuming the vehicle decides to go the same speed in both roundabouts then there would be more time to judge a gap. I would assume the speed would be 15 mph.
Title: Re: Crash prone 'modern roundabouts'
Post by: DaBigE on July 14, 2015, 02:00:06 PM
Larger roundabouts may be safer assuming the entry angles of the roundabout are designed properly and circulating speeds remain low.  Consider the following scenario.  CAR A enters the roundabout mistakenly believing CAR B is about to exit.  Would u want CAR B to take 1.7 seconds or 3.4 seconds to travel the blue path?  More reaction time is a good thing!

95 FT central island diameter:
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Test4_zpshnyyiesp.jpg)

160 FT central island diameter:
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Test3_zpscdfdzp4h.jpg)

You make the assumption that vehicle B will be traveling the same speed in both scenarios. The larger the circle, the faster vehicle B can comfortably travel. The faster vehicle B is traveling, the harder it is for vehicle A to judge the gap.

Your general assumption that drivers feel more comfortable driving faster in larger circles is wrong.  The red min-van may feel comfortable traveling through this circle at 90 mph (in a straight line). 
There was no assumption. Can doesn't mean they necessarily will, but the probability increases.



Relating specifically to modern-roundabouts, the same type of straight line fastest path can occur.  Here’s an example of a small diameter modern-roundabout in Oconomowoc, Wisconsin where the fastest path through the roundabout is approaching a straight line.  I know it sounds counter-intuitive, but larger diameter roundabout can actually slow down the speeds of circulating traffic.

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/fastestpath_zpskfw1ywq5.jpg)

Thanks for helping prove my point by attempting to look at the fast path. Circle size is only part of the equation. The Oconomowoc roundabout also has some path overlap which typically leads to entering crashes as well. This example also shows what tight urban constraints can place on the desirable roundabout size. IIRC, they had to buy out the property in the NW corner. Any larger of a circle, and one or both of the gas stations would have to go as well.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 14, 2015, 07:59:21 PM
Thanks for helping prove my point by attempting to look at the fast path. Circle size is only part of the equation. The Oconomowoc roundabout also has some path overlap which typically leads to entering crashes as well. This example also shows what tight urban constraints can place on the desirable roundabout size. IIRC, they had to buy out the property in the NW corner. Any larger of a circle, and one or both of the gas stations would have to go as well.

If ROW constraints prevent the desired roundabout size from being constructed, maybe it shouldn’t be constructed to begin with.  A traffic signal at Ellsworth & State in Ann Arbor, Michigan that averages 16 crashes a year is a better alternative than a roundabout that experiences 170 crashes in a year.  A similar argument can be made for the roundabout at Auburn & Main in Rockford, Illinois (crashes increased 14X and had nearly 100 crashes in one year). 

Do you have a compelling reason why there has been a significant crash rate at these two roundabouts?  Can you cite a large diameter modern-roundabout that has had 100 crashes in one year?  The fact is the worst performing modern roundabouts have small central island diameters.  Nothing you say will change that fact.
Title: Re: Crash prone 'modern roundabouts'
Post by: DaBigE on July 14, 2015, 09:40:28 PM
If ROW constraints prevent the desired roundabout size from being constructed, maybe it shouldn’t be constructed to begin with.  A traffic signal at Ellsworth & State in Ann Arbor, Michigan that averages 16 crashes a year is a better alternative than a roundabout that experiences 170 crashes in a year.  A similar argument can be made for the roundabout at Auburn & Main in Rockford, Illinois (crashes increased 14X and had nearly 100 crashes in one year).
And no signalized intersection, no interchange ramp design has ever had design compromises? Ever driven a curve that has an advisory speed lower than the speed limit? Design compromises were made in those cases, building a curve smaller than what the laws of physics dictate are safe. Years ago, this ramp (https://www.google.com/maps/dir/43.1346498,-89.2938965/43.1389994,-89.2933386/@43.1377673,-89.2931577,18z/data=!4m2!4m1!3e0) saw several overturns per year (IIRC, there were three that happened in the period of just a few months in one year). Should this interchange not have been constructed because the curves are tighter than desirable? ROW was a big consideration in that case as well. FWIW, the other similar ramps at the same interchange have had near-zero similar overturn incidents.   

Do you have a compelling reason why there has been a significant crash rate at these two roundabouts?  Can you cite a large diameter modern-roundabout that has had 100 crashes in one year?  The fact is the worst performing modern roundabouts have small central island diameters.  Nothing you say will change that fact.
And nothing I have said has disputed that fact. Please stop distorting my comments to fit your agenda. Have you investigated anything other than the size of the central island? What about lane width? As it's been pointed out, ICD is the proper way of classifying a roundabout's size, since the central island is a byproduct of the width of circulatory roadway and the number of circulating lanes. The Oconomowoc example you provided has many other deficiencies besides size (path overlap, fast path, entry deflection, using a mandatory right-turn lane within the regular approach when it should be a partial bypass at the very least...). Looking solely at size is lazy at best, foolish at worst. How many ways do I need to say it before it sinks in (the last time I'm going to say it)...
A roundabout's size MAY indeed be a factor in crashes, but needs additional in-depth study*, in addition to investigating other possible deficiencies.

* More detailed and scientific than can be achieved on this forum and are suitable for publishing in a venue such as a TRB or NCHRP paper.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 14, 2015, 11:30:17 PM
Have you investigated anything other than the size of the central island?

Fastest path:  The fastest path at small central island diameters approaches a straight line.  The Oconomowoc roundabout has a small central island diameter that exemplifies this concept.

Entry deflection angle: Small central island diameters have less pronounced entry deflection angles than larger central island diameter roundabouts.  Just imagine a small neighborhood traffic circle; the entry deflection angle is nearly non-existent. 

Painted spiral markings:  The New York roundabouts cited in this thread have painted spiral markings as opposed to the spiral being designed into the truck apron.  Interestingly, the larger 130’ diameter spiral roundabout in Bethlehem outperformed the smaller 103’ diameter spiral roundabout in Malta (299% vs. 445% increase in crashes respectively). 

Non-interchange vs. interchange roundabouts:  Interchange roundabouts appear to be less accident prone than non-interchange roundabouts.  Some legs at an interchange roundabout only service entry or exiting traffic and it could be argued the turning movements are more predictable (certain turning movements won’t be as heavy).  A pretty strong trend can be seen when looking through the Wisconsin Phase 1 & Phase 2 studies. 

Reducing circulating lanes:  The following crash prone roundabouts have reduced the number of circulating lanes in an attempt to improve safety. 
-14th Street & Superior in Lincoln, Nebraska (3x2 reduced to 2x2)
-Maple & Drake in Farmington Hills, Michigan (3x2 reduced to 2x2)
-Maple & Farmington in Farmington Hills, Michigan (3x2 reduced to 2x2)
-Homer Watson Boulevard and Block Line Road in Kitchener, Ontario (3x2 reduced to 2x2)
-Bailey & Radio in Woodbury, Minnesota (2x2 reduced to 2x1)
-Broadway Avenue & Lake Street in Forrest Lake, Minnesota (2x2 reduced to 1x1)
-Main Ave & Broadway in De Pere, Wisconsin (2x2 reduced to 2x1)

Pavement markings and signage: The study done on the Richfield, Minnesota roundabout at 66th &  Portland has been discussed on this thread multiple times.  The study suggests that standard arrows are less confusing to drivers than fishhooks (the most recent repaving at this intersection includes fishhook arrows though :? ).   

Reaction time: Larger roundabouts may be safer assuming the entry angles of the roundabout are designed properly and circulating speeds remain low.  Consider the following scenario.  CAR A enters the roundabout mistakenly believing CAR B is about to exit.  Would u want CAR B to take 1.7 seconds or 3.4 seconds to travel the blue path?  More reaction time is a good thing!

95 FT central island diameter:
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Test4_zpshnyyiesp.jpg)

160 FT central island diameter:
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Test3_zpscdfdzp4h.jpg)

YES.
Title: Re: Crash prone 'modern roundabouts'
Post by: DaBigE on July 14, 2015, 11:55:02 PM
Have you investigated anything other than the size of the central island?
...
YES.
No, you have not. What you have reiterated are more generalities for a small sample of intersections. When I say investigate, I mean take all of the crash-prone roundabouts and investigate each roundabouts features: fast path speeds, deflection, path overlap, lane configuration, signing, pavement marking, PHI-angles, in addition to size. See how each of those characteristics compare to roundabouts with low/"acceptable" crash rates as well as what the current desirable metrics are for each. Size alone may or may not be the presiding factor in these cases. Making the circle arbitrarily larger will do you no good if you have poor speed control on the approach and/or bad path overlap.

Until then, or some new information comes to light that has not been beaten to death in the last 8 pages, I am done. We're going in circles. As I and roadfro have said, we've taken this size discussion as far as one can in an enthusiast setting.
Title: Re: Crash prone 'modern roundabouts'
Post by: iBallasticwolf2 on July 15, 2015, 09:07:32 AM

We're going in circles.

OH the irony!
Title: Re: Crash prone 'modern roundabouts'
Post by: Rothman on July 15, 2015, 09:24:17 AM

We're going in circles.

OH the irony humanity!

FTFY.
Title: Re: Crash prone 'modern roundabouts'
Post by: iBallasticwolf2 on July 15, 2015, 09:29:01 AM

We're going in circles.

OH the irony humanity!

FTFY.

Well done.
Title: Re: Crash prone 'modern roundabouts'
Post by: DaBigE on July 15, 2015, 09:33:25 AM

We're going in circles.

OH the irony humanity!

FTFY.

Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 15, 2015, 10:36:13 AM
No, you have not. What you have reiterated are more generalities for a small sample of intersections. When I say investigate, I mean take all of the crash-prone roundabouts and investigate each roundabouts features: fast path speeds, deflection, path overlap, lane configuration, signing, pavement marking, PHI-angles, in addition to size.

The study done by the IIHS in 2000 analyzed a small sample of intersections as well.  That study has been embraced by the engineering community and is routinely cited in DOT websites and a link to the study can be found on the FHWA website.  The study looked at the before/after crash data of 24 total roundabouts (15 single lane, and 9 multi-lane) using the empirical Bayes approach.  It didn’t consider fast path speeds, deflection angles, path overlap, signing, pavement marking, PHI-angles, or size.  The conclusion of the study is that total crashes reduce by 39%, injury crashes reduce by 76%, and fatal crashes reduce by 90%. 

http://safety.fhwa.dot.gov/intersection/resources/fhwasa09027/resources/Crash%20Reductions%20Following%20Installation%20of%20Roundabouts.pdf

This thread, more than anything, highlights the fact that the IIHS study in 2000 is too limited in their analysis (and is heavily skewed towards single-lane roundabouts).  It should be painfully obvious that it is unlikely the high capacity 2x2 roundabouts being built today will see a 39% reduction in total crashes.  It should also be obvious that bigger roundabouts appear to perform better than smaller roundabouts.  Ultimately, the worst performing roundabouts in America have small central island diameters.  This is a simple fact that is difficult to dispute.


Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 16, 2015, 12:42:53 PM
Based on MnDot’s “critical crash rate index”, the 3rd most dangerous intersection in the Twin Cities metro for 2013 was at a double-lane roundabout at U.S. 61 & Broadway Avenue in Forest Lake.

http://kstp.com/article/stories/s3699209.shtml

The roundabout has a central island diameter of only 94 feet.  The fix?  They converted it to a single lane roundabout.  At least half-a-dozen examples have been cited of high crash rate roundabouts that have had circulating lanes removed.  Keep in mind, there are only about 40 high capacity 2x2 or 3x2 non-interchange roundabouts in America.  That means roughly 10% of the high capacity non-interchange roundabouts have had circulating lanes removed.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 21, 2015, 11:45:04 AM
Here's an analysis of some multi-lane roundabouts in Oregon.  A multi-lane roundabout in Astoria, Oregon saw a 125% increase in injury crashes.  Another multi-lane roundabout in Springfield, Oregon had a crash rate of 2.91 MEV.  As a comparison, here is a list of major Springfield intersections with their corresponding crash rates.

(http://alexforfg.com/wp-content/uploads/2014/12/springfieldtsp.jpg)
http://alexforfg.com/more-troubling-statistics-on-oregons-dual-lane-roundabouts/
Title: Re: Crash prone 'modern roundabouts'
Post by: Bickendan on July 21, 2015, 01:05:10 PM
Coe Circle doesn't even make the list. I wonder why that is...

Edit: So this is at the top of Oregon's list:
(http://alexforfg.com/wp-content/uploads/2014/12/SpringfieldRoundabout.jpg)

One thing that would greatly help: swapping out the yield signs with stop signs.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 21, 2015, 01:39:26 PM
Coe Circle doesn't even make the list. I wonder why that is...

Edit: So this is at the top of Oregon's list:
(http://alexforfg.com/wp-content/uploads/2014/12/SpringfieldRoundabout.jpg)

One thing that would greatly help: swapping out the yield signs with stop signs.

A few other potential ways to improve safety at this roundabout. 

#1.  Convert it to a 4-leg roundabout and remove access from Wayside Ln. (traffic can divert to Manor Drive to enter onto Hayden Bridge Way). 

#2.  Redesign the central island to be a true spiral roundabout (don't just rely on pavement markings to do the job).
Title: Re: Crash prone 'modern roundabouts'
Post by: Bickendan on July 21, 2015, 02:20:36 PM
Agreed, but I think the number one improvement is stop signs. Yield signs in these situations just promotes drivers risking their chances and trying to beat a car already in the roundabout. Coe Circle uses stop signs, and while drivers do 'California stops' if there aren't any cars already in the roundabout, they do keep an eye out and wait their turn. It also makes it more bicycle friendly.
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on July 21, 2015, 02:30:41 PM
It helps to know where/how most of the accidents are happening.  If there's one entry point that's causing the vast majority of crashes, then they should try to deal with the problem rather than masking a solution.
Title: Re: Crash prone 'modern roundabouts'
Post by: english si on July 21, 2015, 02:55:20 PM
It helps to know where/how most of the accidents are happening.  If there's one entry point that's causing the vast majority of crashes, then they should try to deal with the problem rather than masking a solution.
Indeed, and without knowing the severity of the crashes, and the statistics now, they are meaningless. We're looking at 05-09 data there - modern roundabouts were very rare in the US around that period - could the answer be found in education failures rather than the engineering ones that Tradephoric thinks exist?

Junctions like this work all the time in the UK with near-zero levels of crashes - the existence of a round central island, or Wayside Lane probably are red herrings.
It also makes it more bicycle friendly.
STOP signs make nothing more bicycle friendly unless they don't have to - starting from a stop is not only tiring, but leaves the rider more erratic and vunerable as they build up the inertia that they lost by stopping (a yield isn't so bad if they just have to slow down to a slow speed, rather than come to a complete stop). The issue isn't the type of signs used anyway, it's drivers ignoring them...

It doesn't help matters that the US uses STOP like the boy who cried wolf - so YIELD is basically ignored because conflicts that should be simple yields demand you stop, therefore if it's a yield, there won't be any danger.
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on July 21, 2015, 05:33:10 PM
It doesn't help matters that the US uses STOP like the boy who cried wolf - so YIELD is basically ignored because conflicts that should be simple yields demand you stop, therefore if it's a yield, there won't be any danger.

I can't help but think that wider use of the yield sign might help with roundabout education. I don't think enough drivers encounter "yield" situations enough on their daily drive enough for them to comprehend them at roundabouts.



Of course, does anything really need to be done? If we keep tackling intersections on top of "the list", we'll eventually go through every intersection in the city. I've said this before, and I'll say it again: roundabouts have more crashes because drivers aren't as familiar with them as typical four-way junctions (Coe Circle is a four way junction in my book). The two ways to tackle increased collisions at roundabouts is to do;

A) nothing, and drivers will eventually figure out what to do (this could take 10 to 20 years); and/or
B) build more roundabouts so drivers become more familiar with them.
Title: Re: Crash prone 'modern roundabouts'
Post by: Bickendan on July 21, 2015, 05:58:36 PM
Junctions like this work all the time in the UK with near-zero levels of crashes - the existence of a round central island, or Wayside Lane probably are red herrings.The issue isn't the type of signs used anyway, it's drivers ignoring them...

It doesn't help matters that the US uses STOP like the boy who cried wolf - so YIELD is basically ignored because conflicts that should be simple yields demand you stop, therefore if it's a yield, there won't be any danger.

These hit the nail on the head. As a biker myself, I don't regard having to come to a complete stop at a red light or stop sign an issue. Bikers that complain about it are the ones that will blow through a red light anyway, and I don't have much sympathy for them when something happens.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 23, 2015, 11:13:33 AM
Indeed, and without knowing the severity of the crashes, and the statistics now, they are meaningless.

The link broke down the roundabouts by crash severity (K, A, B, C, O).  The detailed crash severity data isn't ‘meaningless’.

We're looking at 05-09 data there - modern roundabouts were very rare in the US around that period –

There were over 2,000 modern roundabouts in America by the end of 2005.  Of course ‘very rare’ is a vague term that makes your statement difficult to dispute.

could the answer be found in education failures rather than the engineering ones that Tradephoric thinks exist?  Junctions like this work all the time in the UK with near-zero levels of crashes - the existence of a round central island, or Wayside Lane probably are red herrings.

A roundabout outside Farndon, UK has seen 150 crashes since it was redesigned in June, 2012.  This is on par with some of the worst performing roundabouts cited on this thread.  The British people have had 50+ years to perfect yield-at-entry roundabouts and should be well educated in their use.

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Fardon_zpsyiyqhpfa.png)
http://newarkadvertiser.co.uk/articles/news/A46-Farndon-roundabout-layout-will-be-changed
Title: Re: Crash prone 'modern roundabouts'
Post by: english si on July 23, 2015, 01:01:41 PM
The link broke down the roundabouts by crash severity (K, A, B, C, O).
But doesn't have current data? What use is 5-year data from years ago good for unless you also have current data to see whether figures have decreased or not? Even if there's not a downward trend as more people understand how the junction works, then you are still arguing for rebuilding the junction because 6 years ago there were a lot of crashes.
Quote
The detailed crash severity data isn't ‘meaningless’.
You are interpreting words worse than you interpret statistics: I explicitly said that without severity data, the figures are meaningless - not that severity data is meaningless.
Quote
There were over 2,000 modern roundabouts in America by the end of 2005.  Of course ‘very rare’ is a vague term that makes your statement difficult to dispute.
Keep in mind, there are only about 40 high capacity 2x2 or 3x2 non-interchange roundabouts in America.
I am keeping that mind, and then you attack me for doing so! You harp on about multi-lane (and specifically those ones) roundabouts being dangerous death traps, but as well as the (inevitable) small samples, you aren't accounting for unfamiliarity.

A figure of 40 today suggests 'very rare' is highly unlikely to be false 10 years ago.

Of course it's not precise - I couldn't be bothered to do a detailed and time-consuming analysis of how many junctions in the US there were, what proportion of them were roundabouts and factor in regional data - if there was 20000 of them in Florida, then a handful in Oregon will still mean that they aren't commonly occurred by drivers in the area. However, 'very rare' is a qualitative phrase not a quantitative one and therefore more meaningful - your figure of over 2000 roundabouts is a fairly precise quantitative one, but it is meaningless without knowing whether in this context 2000 is big or small.
Quote
A roundabout outside Farndon, UK has seen 150 crashes since it was redesigned in June, 2012.  This is on par with some of the worst performing roundabouts cited on this thread.
I'm a roadgeek, and I went "where the fuck is that" (it's a tiny hamlet): about as descriptive as 'Bob's Farm, USA'. Thankfully you gave an article, so I could know that it is the Farndon Roundabout near Newark, Notts.

That roundabout sees 29900 Vehicles/average weekday on the new A46 leg with high levels of trucks (26200 a year after opening on the A46 north of the roundabout, 13200 on the B6166, 2950 on the old route), making this junction 13.2MEV in that first year and roughly 3 crashes/MEV. That is truly awful (though this, like the Oregon example above seems to be, is a clear outlier).

Looking, the most obvious safety improvement would be to put in the yellow rumble strips that exist almost every time a long (and many not-very long) grade-separated route ends at a roundabout. I can't help but think that 70mph+ traffic on a well-aligned freeway-quality trunk road coming arriving at the roundabout without realising it was that close is going to be a factor in why there is a high level of crashes there.

There's narrow lanes on, and an atypical (I think - it might be common to spiral unsignalised roundabouts in that neck of the woods, but I cannot think of any around here) design of, the circulatory carriageway.

There's also the merging issue just north of the roundabout, where two lanes of trunk road traffic (there was only one before, save for at the roundabout) are forced into one lane. And the article says that the surface was poorly done and anti-skid lost.

So lots of possible factors here as to why this roundabout has become a lot more dangerous - some of which you recommend as safety features, others of which you totally and completely ignore.

If you look at it on google's satellite imagery then you'll see that the old roundabout had a much smaller circulatory carriageway and 3 lanes on it - both of which have been your go-to "these are problems for safety".

And, of course, it really needed to be a GSJ (and was certainly seen in the planning as a fairly temporary junction, though no plans have been sorted on finishing the corridor)
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 23, 2015, 02:50:19 PM

A reoccurring argument in this thread is that crashes at American roundabouts are due to driver unfamiliarity.   It’s the “dumb American” argument.  Yet when a roundabout with a high crash rate is cited from the UK, the focus shifts entirely to design:

Looking, the most obvious safety improvement would be to put in the yellow rumble strips that exist almost every time a long (and many not-very long) grade-separated route ends at a roundabout. I can't help but think that 70mph+ traffic on a well-aligned freeway-quality trunk road coming arriving at the roundabout without realising it was that close is going to be a factor in why there is a high level of crashes there.

There's narrow lanes on, and an atypical (I think - it might be common to spiral unsignalised roundabouts in that neck of the woods, but I cannot think of any around here) design of, the circulatory carriageway.

There's also the merging issue just north of the roundabout, where two lanes of trunk road traffic (there was only one before, save for at the roundabout) are forced into one lane. And the article says that the surface was poorly done and anti-skid lost.

So lots of possible factors here as to why this roundabout has become a lot more dangerous - some of which you recommend as safety features, others of which you totally and completely ignore.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 23, 2015, 02:51:02 PM
If you look at it on google's satellite imagery then you'll see that the old roundabout had a much smaller circulatory carriageway and 3 lanes on it - both of which have been your go-to "these are problems for safety".

Just to be clear, this is the roundabout in question right? 
https://www.google.com/maps/@53.06409,-0.83613,131m/data=!3m1!1e3

The old roundabout did not have 3-cirulating lanes of traffic.  In addition, the central island diameter of the old roundabout was 135 feet (much larger diameter than 100 feet).  IMO, the size of this roundabout looks pretty decent.
Title: Re: Crash prone 'modern roundabouts'
Post by: Tarkus on July 23, 2015, 03:30:16 PM
The link broke down the roundabouts by crash severity (K, A, B, C, O).
But doesn't have current data? What use is 5-year data from years ago good for unless you also have current data to see whether figures have decreased or not? Even if there's not a downward trend as more people understand how the junction works, then you are still arguing for rebuilding the junction because 6 years ago there were a lot of crashes.ugh no plans have been sorted on finishing the corridor)

The bit tradephoric showed in the post was the initial stats from when the roundabout first opened, from the City of Springfield's Transportation System Plan.  If you follow the link, you'll find that there's further stats from the period of 1/1/2009 to 12/31/2013 (the most recent that were available then).  The actual PDFs from the ODOT Crash Reporting system are also linked for the various legs.  The KABCO stats in the main post are an aggregate of all the legs during that latter reporting period.  Pioneer Pkwy W/Hayden Bridge had 46 total (http://alexforfg.com/wp-content/uploads/2014/12/Pioneer-Pkwy-W-and-Hayden-Bridge-KABCO.pdf), Pioneer Pkwy E/Hayden Bridge had 78 total (http://alexforfg.com/wp-content/uploads/2014/12/Pioneer-Pkwy-E-and-Hayden-Bridge-KABCO.pdf), and there's 57 more crashes (http://alexforfg.com/wp-content/uploads/2014/12/MLK-and-Hayden-Bridge-KABCO.pdf) associated with MLK/Hayden Bridge (whether this is at the NW corner or NE corner is unclear, due to how ODOT compiled things).
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on July 23, 2015, 05:57:25 PM
A reoccurring argument in this thread is that crashes at American roundabouts are due to driver unfamiliarity.   It’s the “dumb American” argument.  Yet when a roundabout with a high crash rate is cited from the UK, the focus shifts entirely to design:

Are you suggesting that UK drivers are unfamiliar with roundabouts? Or that US drivers understand them perfectly and that design is entirely to blame?
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 24, 2015, 11:02:53 AM
Are you suggesting that UK drivers are unfamiliar with roundabouts? Or that US drivers understand them perfectly and that design is entirely to blame?

I’m suggesting that the ‘driver unfamiliarity’ argument is masking poor design.  Take another look at the aerial footage of the DePere roundabout.  At 4 seconds in the video, a yellow semi pulls up and waits for a gap in traffic to enter the roundabout.  The semi enters the roundabout at the 12 second mark and forces circulating vehicles to nearly come to a complete stop.  If one of the circulating drivers couldn’t stop in time and struck the semi, the semi driver would be cited for ‘failure to yield.  Did the yellow semi really do anything wrong here?  During rush hours, do we expect the yellow semi to wait 15 minutes for traffic to clear all legs of the roundabout before pulling out?   It’s a design that forces some drivers (IE. larger vehicles during rush hour) to play Russian Roulette (the bullet being a circulating driver not paying attention).


The theory is if the roundabout was bigger (and there was greater distance between legs), circulating traffic will have more time to react when a semi tries to squeeze into the roundabout (and if properly designed, a larger roundabout doesn’t mean circulating speeds are faster… they could actually be slower since entry deflection angles can be more pronounced at large diameter roundabouts).  Sure, some drivers will still enter the roundabout without even looking and run straight into a circulating vehicle, but some of the failure to yield crashes might be prevented with a larger central island diameter.  There has to be reasons why so many multi-lane roundabouts with central-island diameters of 100 feet or less have performed so poorly.  The idea that we just ignore failure to yield crashes and chalk it up to ‘driver unfamiliarity’ doesn’t sit well with me. 
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on July 24, 2015, 11:19:35 AM
Are you suggesting that UK drivers are unfamiliar with roundabouts? Or that US drivers understand them perfectly and that design is entirely to blame?

I’m suggesting that the ‘driver unfamiliarity’ argument is masking poor design.  Take another look at the aerial footage of the DePere roundabout.  At 4 seconds in the video, a yellow semi pulls up and waits for a gap in traffic to enter the roundabout.  The semi enters the roundabout at the 12 second mark and forces circulating vehicles to nearly come to a complete stop.  If one of the circulating drivers couldn’t stop in time and struck the semi, the semi driver would be cited for ‘failure to yield.  Did the yellow semi really do anything wrong here?  During rush hours, do we expect the yellow semi to wait 15 minutes for traffic to clear all legs of the roundabout before pulling out?   It’s a design that forces some drivers (IE. larger vehicles during rush hour) to play Russian Roulette (the bullet being a circulating driver not paying attention).


The theory is if the roundabout was bigger (and there was greater distance between legs), circulating traffic will have more time to react when a semi tries to squeeze into the roundabout (and if properly designed, a larger roundabout doesn’t mean circulating speeds are faster… they could actually be slower since entry deflection angles can be more pronounced at large diameter roundabouts).  Sure, some drivers will still enter the roundabout without even looking and run straight into a circulating vehicle, but some of the failure to yield crashes might be prevented with a larger central island diameter.  There has to be reasons why so many multi-lane roundabouts with central-island diameters of 100 feet or less have performed so poorly.  The idea that we just ignore failure to yield crashes and chalk it up to ‘driver unfamiliarity’ doesn’t sit well with me. 


Looking at this video, the "circulating" vehicles were just coming out of a yield at the same time.  They paused for a few seconds, and everyone went on their merry way.  It's really not a huge deal.

You are always going to have examples where certain vehicles - such as trucks - are going to have it a little hard.  At a traditional 4 way intersection, trucks occasionally have to swing out from the right lane in order to make their right turn without going up and hitting anything on the curb.  If they hit something on the curb, or a vehicle in another lane, they'll be in the wrong then also.  Yes, intersections are designed when possible so that trucks don't have to do this.  But in tight street environments such as cities, there's no way around this happening.

You simply can't compensate for every possible scenario out there.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 24, 2015, 01:15:10 PM
Looking at this video, the "circulating" vehicles were just coming out of a yield at the same time.  They paused for a few seconds, and everyone went on their merry way.  It's really not a huge deal.

It’s not a huge deal to stop in the middle of a roundabout to let in a semi, but it’s an annoyance that increases the likelihood of a crash.  Consider the following scenario. The car and semi pull into the roundabout at the same time.  Would u want the car to take 3.3 seconds or 5.8 seconds to travel the blue path?  The additional 2.5 seconds of reaction time at the larger diameter roundabout may allow the car to simply let off the gas to let the semi in (as opposed to coming to a stop in the middle of the roundabout). 

Would an additional 2.5 seconds of reaction time potentially prevent a crash?  I think so.

115 FT central island diameter:
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/smalldia_zpsgcepbzkj.jpg)

160 FT central island diameter:
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/largedia_zpslxkme5do.jpg)
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on July 24, 2015, 01:19:28 PM
Looking at this video, the "circulating" vehicles were just coming out of a yield at the same time.  They paused for a few seconds, and everyone went on their merry way.  It's really not a huge deal.

It’s not a huge deal to stop in the middle of a roundabout to let in a semi, but it’s an annoyance that increases the likelihood of a crash.  Consider the following scenario. The car and semi pull into the roundabout at the same time.  Would u want the car to take 3.3 seconds or 5.8 seconds to travel the blue path?  The additional 2.5 seconds of reaction time at the larger diameter roundabout may allow the car to simply let off the gas to let the semi in (as opposed to coming to a stop in the middle of the roundabout). 

Would an additional 2.5 seconds of reaction time potentially prevent a crash?  I think so.

The f'ing cars didn't crash into the f'ing truck.  There was no potential crash that could've potentially been avoided.  What's your point?
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on July 24, 2015, 02:01:54 PM
I don't think roundabouts are the only place where trucks tend to try and squeeze into gaps that aren't big enough for them. But they are much larger than cars so they'll win. That, and sometimes with roundabouts, the throughput rate is so high that a reasonable gap for a truck may never form, even with a large roundabout (though perhaps a roundabout the size of the UK one above may permit gaps large enough...not sure).

Basically, I don't think this is a problem that needs solving.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 27, 2015, 11:40:09 AM
The f'ing cars didn't crash into the f'ing truck.  There was no potential crash that could've potentially been avoided.  What's your point?

I’m trying to lay out an explanation why small diameter roundabouts have performed so poorly.  The truck pulling out into the roundabout forced circulating vehicles to take evasive action to avoid a crash (IE. applying the brakes and nearly coming to a complete stop in the roundabout).  If the roundabout had a larger diameter (and it took an additional 2.5 seconds for circulating vehicles to encounter the semi), evasive action could be avoided.  Relying on vehicles to take evasive action to avoid a crash isn’t a great scenario and increases the potential of a crash.  In the end, 2x2 roundabouts with central island diameters of 100 feet or less have seen crashes increase by 500%, 800%, up to 1400%.  That’s not a good track record.  The fact that the cars didn’t hit the truck in the video doesn’t invalidate the point. 
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 31, 2015, 11:56:46 AM
Crashes are up at a new 2x2 roundabout at Highway 22 & Madison Ave. in Mankato, Minnesota.  One thing to note is this roundabout has standard pavement markings (as opposed to the fishhook pavement markings).  This is likely a direct result of the study done on the Richfield, Minnesota roundabout that studied the effects of standard vs. fishhook pavement markings. 

The lessons learned from the Richfield, Minnesota roundabout were applied to the Mankato roundabout yet crashes are still up.  What's concerning is officials seem resigned to the fact that accidents will go up at these high volume roundabouts.  Of course, there is something else in common between the Richfield & Mankato roundabouts.... small central island diameters.  Perhaps officials should focus on the size of the roundabouts before resigning themselves to the fact that accidents will increase at these roundabouts.  Don't accept mediocre performance.

Quote
The tradeoffs were discussed in the planning stages of the roundabouts. In exchange for more accidents, the roundabout would make said crashes much safer. And improve traffic flow.
http://www.keyc.com/story/28328544/crashes-at-mn-hwy-22-more-frequent-but-much-safer

Sure, it's great that roundabouts reduce injury crashes, but which would you prefer?

A.)  A roundabout with a central island diameter of 150 feet that has 20 crashes and 1 injury crash.
B.)  A roundabout with a central island diameter of 100 feet that has 60 crashes and 1 injury crash. 

I'll pick Option A.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on August 03, 2015, 11:07:19 AM
The lowest crash rate roundabouts on this thread have had central island diameters between 130 and 200 feet.  This equates to Inscribed Circle Diameters of roughly 200 to 300 feet (60 to 90 meters).   Take a look at the graph below that looks at the crash rate of Czech Republic roundabouts in relation to their inscribed diameter.  The multi-lane roundabouts with ICD’s between 60 to 90 meters perform well.  Smaller than 60 meters and the crash rate goes up; larger than 90 meters and the crash rate goes up. 
 
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Czech_zpsze2irpjn.png)
http://www.degruyter.com/view/j/tvsb.2010.x.issue-1/v10160-010-0009-0/v10160-010-0009-0.xml

The ‘goldilocks’ inscribed circle diameter appears to be between 200 and 300 feet (60 to 90 meters) for multi-lane roundabouts. 
Title: Re: Crash prone 'modern roundabouts'
Post by: Sykotyk on August 03, 2015, 07:18:38 PM
Rotaries in the northeast work very well. I like them, such as this one I drove on US44 just east of I-495. I drove it east and west, and though traffic seemed to be endless from it, it cleared out well because of the spacing between entry points (though I really think that Friendly's entrance should be closed and only access it from the side road).

https://www.google.com/maps/place/Plympton,+MA/@41.9027404,-70.9590075,19z/data=!3m1!1e3!4m2!3m1!1s0x89e497d5f44178cb:0x3d50f1892f6c5149

The smaller modern roundabouts aren't safe because drivers treat a yield sign as nothing. Just as an on-ramp has a yield sign, the mindset is if you can get in front of that car, you can speed up and get in front of them. This is tolerated on freeway on-ramps, but dangerous in roundabouts.

The idea you must 'yield' to traffic in the circle only makes it worse. The goal then, is to get in that circle at all costs, so everyone else has to yield to you. Small traffic circles, though with a yield sign, should be treated just the same as a four-way stop. Each entry point taking turns letting one car into the circle (regardless which exit point the cars take). You can have more in the circle than one car, but traffic to your right gets to go first (i.e., you yield to the next entry point).

But, our signage laws AND the way our drivers use those signs is not possible. Yield doesn't mean yield to most drivers. I've seen roundabouts where a line of 5-10-15-20 cars all breeze into a roundabout from one entrypoint, choking the entire thing because nobody else can go until every last car gets through from that one point. Meanwhile, traffic backed up the other entry points, and as soon as they got their shot, they floored it. Only for two entry points to clog the center, not allowing any new traffic in as that initial burst had to disperse.

A four-way stop with each entrypoint alternating N/S to E/W with left turn traffic yielding to through and right turn traffic first would been the most efficient means to clear our a huddled intersection.

Title: Re: Crash prone 'modern roundabouts'
Post by: realjd on August 03, 2015, 08:08:21 PM
Rotaries in the northeast work very well. I like them, such as this one I drove on US44 just east of I-495. I drove it east and west, and though traffic seemed to be endless from it, it cleared out well because of the spacing between entry points (though I really think that Friendly's entrance should be closed and only access it from the side road).

https://www.google.com/maps/place/Plympton,+MA/@41.9027404,-70.9590075,19z/data=!3m1!1e3!4m2!3m1!1s0x89e497d5f44178cb:0x3d50f1892f6c5149

The smaller modern roundabouts aren't safe because drivers treat a yield sign as nothing. Just as an on-ramp has a yield sign, the mindset is if you can get in front of that car, you can speed up and get in front of them. This is tolerated on freeway on-ramps, but dangerous in roundabouts.

The idea you must 'yield' to traffic in the circle only makes it worse. The goal then, is to get in that circle at all costs, so everyone else has to yield to you. Small traffic circles, though with a yield sign, should be treated just the same as a four-way stop. Each entry point taking turns letting one car into the circle (regardless which exit point the cars take). You can have more in the circle than one car, but traffic to your right gets to go first (i.e., you yield to the next entry point).

But, our signage laws AND the way our drivers use those signs is not possible. Yield doesn't mean yield to most drivers. I've seen roundabouts where a line of 5-10-15-20 cars all breeze into a roundabout from one entrypoint, choking the entire thing because nobody else can go until every last car gets through from that one point. Meanwhile, traffic backed up the other entry points, and as soon as they got their shot, they floored it. Only for two entry points to clog the center, not allowing any new traffic in as that initial burst had to disperse.

A four-way stop with each entrypoint alternating N/S to E/W with left turn traffic yielding to through and right turn traffic first would been the most efficient means to clear our a huddled intersection.



On small roundabouts, you don't treat them as a 4 way stop. You treat them as a roundabout. If two cars arrive at exactly the same time, it's still treated as a roundabout, i.e. yield to the car on the left.

Where do they put yield signs at the top of on ramps? That's dumb. It's a merge, not a yield.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on August 03, 2015, 09:41:51 PM
Rotaries in the northeast work very well. I like them, such as this one I drove on US44 just east of I-495. I drove it east and west, and though traffic seemed to be endless from it, it cleared out well because of the spacing between entry points (though I really think that Friendly's entrance should be closed and only access it from the side road).

https://www.google.com/maps/place/Plympton,+MA/@41.9027404,-70.9590075,19z/data=!3m1!1e3!4m2!3m1!1s0x89e497d5f44178cb:0x3d50f1892f6c5149

The US44 rotary has an abysmal crash record though.  From 2009 to 2011, the rotary averaged 123 crashes a year.  The rotary has a inscribed circle diameter of 400 feet which leads to high circulating speeds. 

Quote
According to the Department of Transportation, approximately 40,000 cars use the rotary each day and there were 58 accidents there a year on average between 2007 and 2009 before the numbers jumped to about 123 a year between 2009 and 2011. Built around 1932, the rotary encircles a green lawn used as an American Legion memorial where flags are periodically flown as a way to honor deceased servicemen and women.

https://www.bostonglobe.com/metro/regionals/south/2014/03/12/after-decades-gridlock-revamped-rotary-middleborough-will-open-region-some-say/6CoApiCZds5HWcPyTyhl2I/story.html

Title: Re: Crash prone 'modern roundabouts'
Post by: johndoe on August 03, 2015, 10:37:37 PM
Here's an interesting article: http://journalstar.com/news/local/govt-and-politics/mayor-picks-elevated-roundabout-for-warlick-intersection/article_064e9de0-f6b5-5bd0-9c6d-8eba655c3c4f.html

It alludes to previous changes at another local roundabout: http://journalstar.com/news/local/fixes-aimed-at-simplifying-superior-street-roundabout/article_088eec03-c54d-5f34-9808-36ffa4ead11c.html
Title: Re: Crash prone 'modern roundabouts'
Post by: Sykotyk on August 04, 2015, 05:17:16 PM
The US44 rotary has an abysmal crash record though.  From 2009 to 2011, the rotary averaged 123 crashes a year.  The rotary has a inscribed circle diameter of 400 feet which leads to high circulating speeds. 

123 crashes may sound impressive... but what's that to traffic volume compared to other rotaries with similar volume?
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on August 04, 2015, 05:48:00 PM
123 crashes may sound impressive... but what's that to traffic volume compared to other rotaries with similar volume?

Assuming the 40,000 volume cited in the article, that equates to 8.4 accidents / million vehicles.  As a general rule, anything over 2 accidents / million vehicles at an intersection is considered high.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on September 12, 2015, 10:26:24 AM
There have been 13 crashes in 1 week at a new multi-lane roundabout in Lakeville Minnesota.   It’s on track to have 676 crashes the first year of operations!  That won’t happen, but it’s still bad PR when you have 13 crashes in a week.

http://kstp.com/article/stories/s3898071.shtml


Many of the design recommendations that are found in the Richfield, MN study (which studied a crash prone 2x2 roundabout) have been implemented in the new roundabout in Lakeville (standard pavement markings are being used as opposed to fishhook markings).  It will be interesting to see if the lessons learned at the 2x2 roundabout in Richfield will be able to reduce the crash rate at the 2x2 roundabout in Lakeville (based on the first week of crash data though, it's not looking good).
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on September 12, 2015, 02:32:26 PM
(based on the first week of crash data though, it's not looking good).

I think it's far too early to be predicting long-term crash data. Hell if I know the stats, but I'm willing to bet that most roundabouts, when they first open, have a spat of collisions as people figure things out. Give them a chance.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on September 14, 2015, 03:01:06 PM
(based on the first week of crash data though, it's not looking good).

I think it's far too early to be predicting long-term crash data. Hell if I know the stats, but I'm willing to bet that most roundabouts, when they first open, have a spat of collisions as people figure things out. Give them a chance.

Every multi-lane (2x2) roundabout cited on this thread where crash data is available has seen an increase in total crashes.  Can you give me a compelling reason why the multi-lane roundabout in Lakeville will be any different?  It’s not too early to predict a trend. 

Driving through a multi-lane roundabout shouldn’t be a foreign experience for most Minneapolis drivers.  There is a multi-lane roundabout 2 miles down the road from the new roundabout in Lakeville.  In addition, there are roughly 30 multi-lane roundabouts in the Minneapolis region. 
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on September 14, 2015, 03:19:30 PM
Every multi-lane (2x2) roundabout cited on this thread where crash data is available has seen an increase in total crashes.  Can you give me a compelling reason why the multi-lane roundabout in Lakeville will be any different?  It’s not too early to predict a trend. 

LOL  :rofl:

Why would someone post about non-accident prone roundabouts on a thread titled "Crash Prone Modern Roundabouts"?  Of course most roundabouts cited on this thread have seen an increase in total crashes.  That's the whole fricken point of this thread.

Should we start up a thread "Non-Accident prone roundabouts"?  Can't wait for the exciting dialogue on that thread.

Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on September 14, 2015, 04:37:13 PM
Previously in this thread, a comprehensive list of 2x2 roundabouts in America was queried out from a database of over 5,100 modern roundabouts.  This was in direct response to a request you had made jeffandNicole.  I attempted to find before/after crash data for each one.  I could only track down crash data for 14 out of the 40, but of those 14, all had an increase in total crashes.

It would probably be fair to see a longer list, which will show both 100' diameter roundabouts that don't have high crash frequencies, and roundabouts with larger diameters and how they rank. 

Here is a list of 40 multi-lane roundabouts that I think could be meaningful to this conversation.  This was queried from a database of over 5,100 modern roundabouts.  This was the criteria used to query out the list:

-roundabouts constructed within the last 10 years
-all approaches have 2 entry lanes
-roundabouts have 4-legs
-main & side streets are major state or county routes (ie. likely high AADT roundabouts)
-interchange roundabouts (and frontage road roundabouts) not included

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/RBtest_zpsbkjmf4ri.png)

Now the hard part is finding accurate before/after crash data to make any type of analysis.  Here is a google KMZ file that includes the 40 roundabouts in the chart above:

http://www.mediafire.com/download/cd570rarros2c3g/Multi-Lane+Roundabouts+%28with+high+AADT%29.kmz


Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on September 14, 2015, 04:44:53 PM
Here's the 14 roundabouts i eventually found crash data for.  Increases in total crashes ranged from 36% to 1400%. 

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/RBDATASummary_zpsg7upbybr.png)
Title: Re: Crash prone 'modern roundabouts'
Post by: johndoe on September 14, 2015, 09:39:42 PM
Interesting data, some of those are shocking!  171 crashes in one year? ! That's hard to believe! (Not doubting you)   Can I ask why you exempted interchanges ?
Title: Re: Crash prone 'modern roundabouts'
Post by: Rothman on September 15, 2015, 01:57:45 PM
Yeah, I questioned the data because I travel through roundabouts on that list frequently (more than once weekly).  If the data was true, I'd come across more accidents than I do, even from just an anecdotal sense.
Title: Re: Crash prone 'modern roundabouts'
Post by: NJRoadfan on September 15, 2015, 03:38:35 PM
After braving this roundabout, I'd have to think there are plenty of accidents: https://goo.gl/maps/7sKaT

Compared to others in the area, it has a small diameter island. Its pretty difficult to "jump in" during rush hour.
Title: Re: Crash prone 'modern roundabouts'
Post by: Mrt90 on September 15, 2015, 04:09:44 PM
This is a two lane roundabout in Pleasant Prairie, Wisconsin.  The problem that I have with this roundabout is that there is an inconsistency regarding which lane(s) can exit the roundabout.  If you exit onto 39th Avenue going north or south or if you exit onto Hwy165 going west you can be in either lane to exit. However, if you are exiting on Hwy165 going east then you must be in the outside lane in order to exit and the inside lane is only to continue in the roundabout.  Why is that one exit different that the other 3?  What usually happens to me is that I'm trying to continue east on Hwy165 so I know that I have to be in the right lane the way the lanes are drawn, but someone will pass me in the inside lane and continue east on Hwy165, cutting me off. If there is another car on the inside I'm basically forced to stop because everyone thinks they can exit from the inside lane, and because of the other roads in the area almost everyone that enters the roundabout from the west is exiting south or east, not north. I'm not sure why the inside lane isn't always a "continue in the roundabout" lane and the outside lane is the only exit lane, but only 1 of the 4 exits in this roundabout is drawn this way.  Is this typical?


https://www.google.com/maps/@42.5225151,-87.8537268,138m/data=!3m1!1e3?hl=en
Title: Re: Crash prone 'modern roundabouts'
Post by: johndoe on September 15, 2015, 05:24:20 PM
Mrt90, it's because of the dual EBL.  (You could argue dual lefts probably aren't necessary because look what happens to those two lanes a whole 50' north of the intersection...)  To me it looks like there are lots of signs and markings; it's unwise for drivers to assume a 2 lane approach always means two through lanes.  If people would drive roundabouts like signals many problems would be minimized.
Title: Re: Crash prone 'modern roundabouts'
Post by: Mrt90 on September 15, 2015, 05:41:18 PM
johndoe I see what you mean, but it probably would have been better if the road going east had two lanes merge into one after the roundabout like the other roads do, so that the exiting lanes were consistent.  The other problem is that if you look at the map the I linked and go a little bit west, there is another roundabout (the link below show both).  So someone going east on Hwy 165 through both roundabouts can use either lane to continue east through the first roundabout, but then is supposed to use only the outside lane to continue east on the 2nd roundabout.  And my experience is that almost everyone gets that 2nd roundabout east exit wrong.  It's probably safer for me to do it incorrectly just like everyone else.

https://www.google.com/maps/@42.5256339,-87.8568222,1106m/data=!3m1!1e3?hl=en
Title: Re: Crash prone 'modern roundabouts'
Post by: UCFKnights on September 16, 2015, 07:42:54 PM
That is among the best signed roundabout I have seen. Hard to believe people are getting that wrong... crazy
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on October 12, 2015, 01:18:01 AM
Found crash data for the multi-lane roundabout at Venice Ave & Jacaranda Blvd.  It has a crash rate of 4.16 (the highest crash rate intersection in Sarasota County).  The county considers any intersection with a crash rate of over 2 as "critical".   

http://www.heraldtribune.com/article/20150815/ARTICLE/150819785

Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on October 12, 2015, 01:36:19 AM
Are there any multi-lane (2x2) roundabout in America where there was a reduction in total crashes?  I'm starting to wonder.
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on October 12, 2015, 02:01:27 AM
Also in the article;

Quote
Oddly, as Bennett noted, a by-product of the roundabout is more lives have been saved even though crash rates skyrocketed. People drive slower in roundabouts – the posted speed limit is 15 mph in Venice — lessening the chance of serious injuries, but the lack of knowledge of how to maneuver them causes plenty of sideswipes and insurance claims in Venice.

Yes, there does seem to be an increase in collisions at 2x2 roundabouts. Fine. But if the overall number of critical-injury collisions is falling, that's good, yes?

Do you have some data for 2x2 roundabouts over time? I seem to remember some previous data that you provided showing overall collisions falling over time. I know this roundabout had 52, 57, and 50 over the last three years (overall # of collisions). So this most recent year was its best ever (despite the previous year being the worst ever). I think we need to give this intersection a few more...uhh, decades, before we declare it a loss.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on October 12, 2015, 11:29:31 AM
Do you have some data for 2x2 roundabouts over time? I seem to remember some previous data that you provided showing overall collisions falling over time. I know this roundabout had 52, 57, and 50 over the last three years (overall # of collisions). So this most recent year was its best ever (despite the previous year being the worst ever). I think we need to give this intersection a few more...uhh, decades, before we declare it a loss.

If an agency is aware that the roundabout has a crash rate of 4.16 (over 2x what they deem "critical") and does nothing to address the problem, they could potentially be found negligent.  “The roundabout will work well in 20 years” is not a strong defense.  The roundabouts best performing year had total crashes 350% higher than when the intersection was signalized.  That’s a bad result.  When total crashes increase by 350%, there is no guarantee that injury crashes will drop (several roundabouts have been cited in this thread where injury crashes have gone up).
Title: Re: Crash prone 'modern roundabouts'
Post by: lordsutch on October 12, 2015, 02:34:23 PM
From jakeroot: "Oddly, as Bennett noted, a by-product of the roundabout is more lives have been saved even though crash rates skyrocketed."

Put that in your negligence and smoke it.
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on October 12, 2015, 02:55:57 PM
Do you have some data for 2x2 roundabouts over time? I seem to remember some previous data that you provided showing overall collisions falling over time. I know this roundabout had 52, 57, and 50 over the last three years (overall # of collisions). So this most recent year was its best ever (despite the previous year being the worst ever). I think we need to give this intersection a few more...uhh, decades, before we declare it a loss.

If an agency is aware that the roundabout has a crash rate of 4.16 (over 2x what they deem "critical") and does nothing to address the problem, they could potentially be found negligent.  “The roundabout will work well in 20 years” is not a strong defense.  The roundabouts best performing year had total crashes 350% higher than when the intersection was signalized.  That’s a bad result.  When total crashes increase by 350%, there is no guarantee that injury crashes will drop (several roundabouts have been cited in this thread where injury crashes have gone up).

But wouldn't an agency be found just as negligent, if not more, for installing an intersection that has been proven to be far deadlier? As an agency, an intersection where more minor injuries occur should be preferable to one where people have been proven to be killed (especially if you consider these Target:Zero campaigns which aim to end traffic fatalities at some point).
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on October 12, 2015, 08:33:41 PM
Sarasota County stated they would review intersections with a crash rate equal to or greater than 2.0 MVE and recommend potential corrective measures for improvements.  This is from page 2 of the 2013-2014 Sarasota Crash Summary Report:

Quote
Crash rates for signalized intersections within the County typically range from a minimum of zero (i.e., no crashes) to approximately 3.5 MVE. Also, past records show that the top 10 intersections generally have crash rates greater than 2.0 MVE. Thus the County considers  a crash rate equal to or greater than 2.0 MVE as a critical rate.  Intersections that exceed this threshold are selected for further study and reviewed to recommend potential corrective measures for improvements.

https://www.scgov.net/PublicWorks/Traffic%20County%20Data/2013%20-%202014%20Summary%20Crash%20Report.pdf

If it can be proven that Sarasota County failed to review an intersection that had a crash rate equal to or greater than 2.0 MVE, then they could be found to be negligent.  It has nothing to do with the ‘injury crash rate’ since that wasn’t the metric selected by Sarasota County.
Title: Re: Crash prone 'modern roundabouts'
Post by: silverback1065 on October 13, 2015, 06:55:21 PM
http://wishtv.com/2015/10/08/roundabouts-may-confuse-but-stats-back-up-their-safety/
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on October 13, 2015, 09:36:13 PM
http://wishtv.com/2015/10/08/roundabouts-may-confuse-but-stats-back-up-their-safety/

My favorite quote(s):

Quote
And even if you make a mistake, because speeds are so slow, most wrecks don’t involve serious injuries....[Carmel Mayor Jim Brainard] points out that because accidents and injuries are down in Carmel, insurance rates have dropped. He says the city doesn’t have a full “jaws of life” crew in its fire department anymore because they don’t have the high speed impacts that they used to have and don’t need them very often.
Title: Re: Crash prone 'modern roundabouts'
Post by: cl94 on October 13, 2015, 10:59:33 PM
http://wishtv.com/2015/10/08/roundabouts-may-confuse-but-stats-back-up-their-safety/

My favorite quote(s):

Quote
And even if you make a mistake, because speeds are so slow, most wrecks don’t involve serious injuries....[Carmel Mayor Jim Brainard] points out that because accidents and injuries are down in Carmel, insurance rates have dropped. He says the city doesn’t have a full “jaws of life” crew in its fire department anymore because they don’t have the high speed impacts that they used to have and don’t need them very often.

What's funny is that many places critical about the introduction of roundabouts think they're great 10-15 years later. I'll give an example from my hometown in Warren County, NY. About 10 years ago, NYSDOT put in a roundabout to replace the 5 way signalized intersection between US 9, NY 9L, and NY 32 at the center of Glens Falls. At first, everyone hated it. Then people realized that the once-common traffic issues were no more, it was easier to walk around downtown, and it put a nice centerpiece in a traditional New England-style town square. Last year, a new roundabout was installed in the town of Queensbury on Aviation Road about 1/2 mile west of I-87 Exit 19, replacing a dangerous acute angle intersection. Now, local media and residents are pushing to have more roundabouts installed in the area, notably in the vicinity of I-87 Exit 20.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on October 14, 2015, 12:17:43 AM
What's funny is that many places critical about the introduction of roundabouts think they're great 10-15 years later. I'll give an example from my hometown in Warren County, NY. About 10 years ago, NYSDOT put in a roundabout to replace the 5 way signalized intersection between US 9, NY 9L, and NY 32 at the center of Glens Falls. At first, everyone hated it. Then people realized that the once-common traffic issues were no more, it was easier to walk around downtown, and it put a nice centerpiece in a traditional New England-style town square. Last year, a new roundabout was installed in the town of Queensbury on Aviation Road about 1/2 mile west of I-87 Exit 19, replacing a dangerous acute angle intersection. Now, local media and residents are pushing to have more roundabouts installed in the area, notably in the vicinity of I-87 Exit 20.

The roundabouts you are referencing are single-lane roundabouts.  Driver's don't have too much trouble with those.  When the region constructs a complex multi-lane roundabout, that's when you might run into problems. 
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on October 14, 2015, 01:09:45 AM
Carmel is the roundabout capital of America and the mayor has been a staunch supporter of roundabouts for years.  The mayor cites safety statistics in this story, but keep in mind the stats are based on studies skewed towards evaluating single-lane roundabouts.   


Carmel roundabouts sound great after watching that story.  The reality is 3 of the top 4 highest crash intersections in Carmel occurred at roundabouts in 2014.  Here’s a list of the worst offenders:

33 crashes - 116th St & Illinois St
36 crashes - Carmel Drive & Keystone Pkwy
49 crashes - Old Meridian St & Pennsylvania
51 crashes - 116th St & Springmill Rd
68 crashes - 116th St & Keystone Pkwy

Carmel Police Department 2014 Annual report (refer to page 23)
http://carmel.in.gov/Modules/ShowDocument.aspx?documentID=5712
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on October 14, 2015, 01:21:31 AM
Carmel roundabouts sound great after watching that story.  The reality is 3 of the top 4 highest crash intersections in Carmel occurred at roundabouts in 2014.  Here’s a list of the worst offenders:

And if you compare those roundabouts to the signals they replaced, the roundabouts are (more than likely) safer. There is nothing wrong with the occasional fender-bender. You can't eliminate those. What you can do, is mitigate severe collisions by removing the possibility of high-speed impacts altogether. Carmel is, according to Brainard (based on my quoted text above), safer as a result of these roundabouts. There may be more collisions, but they are nowhere near as severe as the ones before.

My point being, safety is measured by more than just the number of collisions at an intersection.
Title: Re: Crash prone 'modern roundabouts'
Post by: Rothman on October 14, 2015, 09:05:56 AM
What's funny is that many places critical about the introduction of roundabouts think they're great 10-15 years later. I'll give an example from my hometown in Warren County, NY. About 10 years ago, NYSDOT put in a roundabout to replace the 5 way signalized intersection between US 9, NY 9L, and NY 32 at the center of Glens Falls. At first, everyone hated it. Then people realized that the once-common traffic issues were no more, it was easier to walk around downtown, and it put a nice centerpiece in a traditional New England-style town square. Last year, a new roundabout was installed in the town of Queensbury on Aviation Road about 1/2 mile west of I-87 Exit 19, replacing a dangerous acute angle intersection. Now, local media and residents are pushing to have more roundabouts installed in the area, notably in the vicinity of I-87 Exit 20.

The roundabouts you are referencing are single-lane roundabouts.  Driver's don't have too much trouble with those.  When the region constructs a complex multi-lane roundabout, that's when you might run into problems. 


At least in New York, anything larger than a two-lane roundabout gets scoffed at.  Not sure if we have anything larger than a two-lane roundabout here, but I know they've been outright avoided at significant cost (Washington Ave/Fuller Rd in Albany was considered for a three-lane roundabout before going with a smaller roundabouts and an overpass).
Title: Re: Crash prone 'modern roundabouts'
Post by: cl94 on October 14, 2015, 09:31:35 AM
What's funny is that many places critical about the introduction of roundabouts think they're great 10-15 years later. I'll give an example from my hometown in Warren County, NY. About 10 years ago, NYSDOT put in a roundabout to replace the 5 way signalized intersection between US 9, NY 9L, and NY 32 at the center of Glens Falls. At first, everyone hated it. Then people realized that the once-common traffic issues were no more, it was easier to walk around downtown, and it put a nice centerpiece in a traditional New England-style town square. Last year, a new roundabout was installed in the town of Queensbury on Aviation Road about 1/2 mile west of I-87 Exit 19, replacing a dangerous acute angle intersection. Now, local media and residents are pushing to have more roundabouts installed in the area, notably in the vicinity of I-87 Exit 20.

The roundabouts you are referencing are single-lane roundabouts.  Driver's don't have too much trouble with those.  When the region constructs a complex multi-lane roundabout, that's when you might run into problems. 


At least in New York, anything larger than a two-lane roundabout gets scoffed at.  Not sure if we have anything larger than a two-lane roundabout here, but I know they've been outright avoided at significant cost (Washington Ave/Fuller Rd in Albany was considered for a three-lane roundabout before going with a smaller roundabouts and an overpass).

Jones Beach. Traffic circle was restriped to a 3-lane roundabout.

I can't think of many places in the states off the top of my head with a 3+ lane roundabout. If there's enough traffic to require three lanes, I'd think that some of the benefits would be reduced.
Title: Re: Crash prone 'modern roundabouts'
Post by: Rothman on October 14, 2015, 09:35:34 AM
What's funny is that many places critical about the introduction of roundabouts think they're great 10-15 years later. I'll give an example from my hometown in Warren County, NY. About 10 years ago, NYSDOT put in a roundabout to replace the 5 way signalized intersection between US 9, NY 9L, and NY 32 at the center of Glens Falls. At first, everyone hated it. Then people realized that the once-common traffic issues were no more, it was easier to walk around downtown, and it put a nice centerpiece in a traditional New England-style town square. Last year, a new roundabout was installed in the town of Queensbury on Aviation Road about 1/2 mile west of I-87 Exit 19, replacing a dangerous acute angle intersection. Now, local media and residents are pushing to have more roundabouts installed in the area, notably in the vicinity of I-87 Exit 20.

The roundabouts you are referencing are single-lane roundabouts.  Driver's don't have too much trouble with those.  When the region constructs a complex multi-lane roundabout, that's when you might run into problems. 


At least in New York, anything larger than a two-lane roundabout gets scoffed at.  Not sure if we have anything larger than a two-lane roundabout here, but I know they've been outright avoided at significant cost (Washington Ave/Fuller Rd in Albany was considered for a three-lane roundabout before going with a smaller roundabouts and an overpass).

Jones Beach. Traffic circle was restriped to a 3-lane roundabout.


Go figure.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on October 14, 2015, 11:46:17 AM

And if you compare those roundabouts to the signals they replaced, the roundabouts are (more than likely) safer. There is nothing wrong with the occasional fender-bender. You can't eliminate those. What you can do, is mitigate severe collisions by removing the possibility of high-speed impacts altogether. Carmel is, according to Brainard (based on my quoted text above), safer as a result of these roundabouts. There may be more collisions, but they are nowhere near as severe as the ones before.

My point being, safety is measured by more than just the number of collisions at an intersection.

Listing intersections with the highest crash rate is common when agencies perform annual safety audits.  In many cases, agencies are required to investigate further any intersection that exceeds a predefined critical crash rate.  In the case of WisDOT this critical rate is 2.0 MVE (the same as Sarasota County).  When this threshold is met at a roundabout, agencies may attempt to restripe/resign the roundabout or remove circulating lanes to simplify the operation.  Several examples of removing circulating lanes have already been cited in this thread:

-14th Street & Superior in Lincoln, Nebraska (3x2 reduced to 2x2)
-Maple & Drake in Farmington Hills, Michigan (3x2 reduced to 2x2)
-Maple & Farmington in Farmington Hills, Michigan (3x2 reduced to 2x2)
-Homer Watson Boulevard and Block Line Road in Kitchener, Ontario (3x2 reduced to 2x2)
-Bailey & Radio in Woodbury, Minnesota (2x2 reduced to 2x1)
-Broadway Avenue & Lake Street in Forrest Lake, Minnesota (2x2 reduced to 1x1)
-Main Ave & Broadway in De Pere, Wisconsin (2x2 reduced to 2x1)

Agencies are just following the rules that have been put into place.  If there is a roundabout that exceeds the critical crash rate and nothing is done about it, they are liable to get sued.  I know you believe crash severity is important Jake, and it is, but there are other factors at play here. 
Title: Re: Crash prone 'modern roundabouts'
Post by: silverback1065 on October 14, 2015, 03:20:37 PM
http://www.wthr.com/story/30254415/round-and-round-carmel-man-sets-out-to-set-roundabout-driving-record
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on October 17, 2015, 02:45:06 PM
The roundabout at Livernois & Hamlin in Rochester Hills, Michigan was constructed in 2010.  Since its completion, there has been an increase in both injury and Property Damage Only (PDO) crashes.

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/HamlinampLivernois_zps3b3hh65o.png)
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on October 19, 2015, 05:29:53 PM
A multi-lane roundabout was constructed at Hillsborough Street and Pullen Road near North Carolina State University in 2010.  After 132 fender-benders in two years, they converted it to a single-lane roundabout in 2012.

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/roundabout-intersection-crashes_zpsbj1ugdeu.jpg)

http://www.wral.com/traffic/story/11369528/
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on October 19, 2015, 05:56:42 PM
What are the traffic flow numbers along Hillsborough Street?
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on October 19, 2015, 07:48:19 PM
What are the traffic flow numbers along Hillsborough Street?

According to the 2013 Annual Average Daily Traffic Map, Hillsborough Street corridor had an AADT of 15,000.  The Hillsborough St./Pullen Rd. roundabout averaged 66 crashes per year when it was a multi-lane roundabout. 

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Random/TrafficVolumeRaleigh_zpsfvl908uz.png)
www.ncdot.gov/travel/statemapping/trafficvolumemaps/default.html
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on October 19, 2015, 07:52:35 PM
In addition to the increase in total crashes, the Hillsborough Street roundabout had a 29% increase in injury crashes:

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Random/untitledHillsboroughRoundabout_zpswhhjpl2z.png)
https://connect.ncdot.gov/resources/safety/Safety%20Evaluation%20Projects/Roundabout%20Presentation%20with%20Notes.pdf
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on October 19, 2015, 08:17:09 PM
In addition to the increase in total crashes, the Hillsborough Street roundabout had a 29% increase in injury crashes:

Well, at least the severity dropped. Any fatalities before or after?
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on October 19, 2015, 10:54:50 PM
Well, at least the severity dropped. Any fatalities before or after?

There's no mention of fatal crashes occurring in the study.  The severity index is a weighted average of fatal, injury, and PDO crashes.  An intersection with a low severity index can have more injury accidents than an intersection with a high severity index; assuming the total crashes are disproportionately high at the low severity index intersection.  I believe this is the equation used in the Hillsborough roundabout study:

Severity Index = (76 * F + 8.2 * I + 1* PDO) / N

Where,
F = total number of fatal crashes
I = total number of injury crashes
PDO = total number of personal damage only crashes
N = total number of crashes
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on October 21, 2015, 09:32:59 PM
The roundabout at SC 46 and Bluffton Parkway in Bluffton, SC was converted to a 2x2 roundabout in 2011 (previously 2x1).  After the conversion, the roundabout experienced a higher than expected crash rate.  As a result of the high crash rate, roundabout experts were asked by the FHWA Offices of Safety Peer-to-Peer program to review and provide low-cost modifications to improve safety.  Per the review, pavement marking changes were made in December, 2012.

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/SCroundabout_zpslgjjevwy.png)

http://static1.squarespace.com/static/51cc8d46e4b0b242fc8d0f33/t/55c4febce4b03a1fdb5cadfc/1438973628373/24.+Roundabout+Design+Optimization+for+Safety+and+Operations.pdf

It initially appeared the pavement marking changes were successful at reducing crashes.  There were only 2 crashes at the roundabout the first 6 months after modifications (12/13/12 through 6/1/13).  In 2014, however, there were 30 total crashes including 7 injury collisions.  Ultimately, the Bluffton Parkway roundabout still has a high crash rate and an alarming number of injury collisions in 2014.  The expert modifications done in 2012 hasn't solved the problem.

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/SCroundaboutcrashdata_zpsmsfjddtn.png)

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/SCroundabout2015crashdata_zps39uwro3y.png)

http://www.islandpacket.com/news/local/traffic/article33716778.html
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on October 22, 2015, 05:36:37 PM
After reading through this thread from start to finish, I will agree that there does seem to be discrepancies from what the engineers say to what reality says. But, I'm not sure what the fix is. I'm still convinced that roundabouts get safer with time (which is hard to measure though, since AADT numbers almost always rise with time, so naturally the number of collisions will rise), but do you think we are building too many roundabouts? Would you prefer more signals? Honest question, no premeditation here. I just want to hear what you think the solution to this problem is.
Title: Re: Crash prone 'modern roundabouts'
Post by: silverback1065 on October 22, 2015, 06:16:40 PM
After reading through this thread from start to finish, I will agree that there does seem to be discrepancies from what the engineers say to what reality says. But, I'm not sure what the fix is. I'm still convinced that roundabouts get safer with time (which is hard to measure though, since AADT numbers almost always rise with time, so naturally the number of collisions will rise), but do you think we are building too many roundabouts? Would you prefer more signals? Honest question, no premeditation here. I just want to hear what you think the solution to this problem is.

I'd say build more roundabouts, and educate people how to use them, I guarantee most accidents are because people have no idea what they're doing in them.  Signals are annoying.  Moving from the stop light obsessed Indianapolis to Carmel, I finally see why Brainard is obsessed with them, traffic is so much better.  However, I do admit that roundabouts do not work everywhere though.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on October 23, 2015, 05:40:13 PM
There are 94 roundabouts and counting in Carmel, Indiana.  Of these 94 roundabouts, there are only four multi-lane roundabouts that have two-circulating lanes throughout the entire circle.  Here is crash data for Carmel’s 2x2 multi-lane roundabouts:

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Carmel116thKeystone_zpsmcrormht.png)

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/CarmeCarmel_zpsqeit3r6w.png)

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/CarmelSpringMill_zpsszypdosv.png)

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/CarmelIllinois_zps5lalomr0.png)

Drivers are having trouble navigating the higher capacity multi-lane roundabouts in Carmel.   The roundabout at 116th & Keystone Pkwy averaged 64.3 crashes a year since 2011.  The AADT of 116th Street at Keystone was 20,463 according to Hamilton County’s 2011 traffic count data.  This equates to a crash rate of 8.7 which is off the charts (an intersection crash rate over 2.0 is often considered ‘critical’ and warrants further investigation).
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on October 23, 2015, 05:41:31 PM
After reading through this thread from start to finish, I will agree that there does seem to be discrepancies from what the engineers say to what reality says. But, I'm not sure what the fix is. I'm still convinced that roundabouts get safer with time (which is hard to measure though, since AADT numbers almost always rise with time, so naturally the number of collisions will rise), but do you think we are building too many roundabouts? Would you prefer more signals? Honest question, no premeditation here. I just want to hear what you think the solution to this problem is.

I don’t believe America is building too many roundabouts.  The majority of single-lane and 2x1 multi-lane roundabouts function well and don't have high crash rates.  What has happened is more complex multi-lane (2x2) roundabouts have been constructed in recent years, and these are the roundabouts that are seeing high crash rates.  The good thing is these roundabouts are being monitored closely.  Agencies are addressing these high crash rate roundabouts by eliminating circulating lanes and experimenting with signage/pavement marking changes (many examples of this have already been mentioned on this thread).   
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on October 23, 2015, 05:58:24 PM
Drivers are having trouble navigating the higher capacity multi-lane roundabouts in Carmel.   The roundabout at 116th & Keystone Pkwy averaged 64.3 crashes a year since 2011.  The AADT of 116th Street at Keystone was 20,463 according to Hamilton County’s 2011 traffic count data.  This equates to a crash rate of 8.7 which is off the charts (an intersection crash rate over 2.0 is often considered ‘critical’ and warrants further investigation).

I'm sorry trade, but I just don't think anyone cares. Carmel has basically reduced their traffic fatalities to zero (so far as I know), and they don't have any traffic congestion. If the trade-off is a slight increase in collisions, by all means, most people will take the increase in collisions. But you'll be hard-pressed to find anyone in Carmel who would prefer a traffic signal, with its backups and t-bone collisions. I mean, of course traffic signals have less collisions. They're really fucking easy to navigate (red means stop, green means go), but that doesn't automatically mean it's the preferred choice for multi-lane intersections, just because there's fewer collisions.

It should be noted that Carmel's population has increased by 62% since 2000. Perhaps traffic engineers take a different approach, but personally, I've always viewed the number of collisions at an intersection as a factor of the amount of cars going through it. It should be well established that there are many gaffe-prone drivers out there, so intersections with more people are likely to have to more of these gaffe-prone drivers going through them at any given moment. Given this, it should be no surprise that the busier intersections have more collisions -- there's just more cars.

I don’t believe America is building too many roundabouts.  The majority of single-lane and 2x1 multi-lane roundabouts function well and don't have high crash rates.  What has happened is more complex multi-lane (2x2) roundabouts have been constructed in recent years, and these are the roundabouts that are seeing high crash rates.  The good thing is these roundabouts are being monitored closely.  Agencies are addressing these high crash rate roundabouts by eliminating circulating lanes and experimenting with signage/pavement marking changes (many examples of this have already been mentioned on this thread).

If you take into account my point above, there are more cars in a two or three lane roundabout at any given time than a single lane roundabout. It should be no surprise that there are more collisions -- there's more cars!
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on October 24, 2015, 02:40:33 AM
The crash rate measures the number of crashes at an intersection per million entering vehicles.  Engineers like to see crash rates below 2.0 MEV.  What are the crash rates for the following intersections Jake?

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/BBcrash7_zpsxolkyssw.png)

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/BBcrashdata_zpsdswiwuqc.png)
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on October 26, 2015, 05:02:54 AM
The crash rate measures the number of crashes at an intersection per million entering vehicles.  Engineers like to see crash rates below 2.0 MEV.  What are the crash rates for the following intersections Jake?

Fuck if I know. I'm horrible at math. But I do know that the Troy junction does not permit left or U-turns, so comparing the two is like comparing apples to oranges. The bottom intersection is not necessarily a full-fledged four-way junction like the roundabout.

Then again, my theory from my previous post is just that: a theory. I didn't attempt to back it up with evidence. It's just a hunch. I can't imagine it's always true (that is, busier intersections have more collisions).

But, still, I maintain that the crash rate is far less important than the death rate. Very few of your stats ever show fatalities (and if they do, it's usually zero for both before and after the roundabout). At that point, it should come down to A) when possible, avoiding the intersection design which has the likelihood of creating the greatest potential for death, and B) which intersection design has the best vehicle through-put.

Now, I've basically created my own criteria by which I judge safety (which may or may not be a straw-man). But, I do more than likely represent the majority of people, who would take an uptick in collisions if it meant basically eliminating traffic fatalities.
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on October 26, 2015, 05:50:00 AM
Can you please analyze some of Washington's roundabouts? As usual, I have no idea where to find those AADT numbers, nor the crash rates. I know back on the first or second page, you pulled some numbers for some roundabouts in Washingotn, but the numbers were over a decade old, and I'm interested to see whether or not any new developments have occurred since then.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on October 26, 2015, 12:16:03 PM
The Bluffton roundabout has a crash rate of 3.41 which is 4X the average crash rate of signalized intersections.  This is more than just a ‘slight increase in collisions'.  The injury crash rate at the Bluffton roundabout is 0.54 which is approaching the total crash rate of signalized intersections.  It’s not a good result.

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/avgcrashrate_zpsttjvtneh.png)
https://www.massdot.state.ma.us/highway/Departments/TrafficandSafetyEngineering/CrashData/CrashRates/Intersection.aspx

I'm sorry trade, but I just don't think anyone cares. Carmel has basically reduced their traffic fatalities to zero (so far as I know), and they don't have any traffic congestion. If the trade-off is a slight increase in collisions, by all means, most people will take the increase in collisions. But you'll be hard-pressed to find anyone in Carmel who would prefer a traffic signal, with its backups and t-bone collisions. I mean, of course traffic signals have less collisions. They're really fucking easy to navigate (red means stop, green means go), but that doesn't automatically mean it's the preferred choice for multi-lane intersections, just because there's fewer collisions.

Carmel has seen a drop in injury accidents and city officials attribute the drop in to its roundabout-building initiative.  I’m not surprised as the vast majority of Carmel roundabouts function well.  However, there are a handful of Carmel roundabouts with high crash rates.  These problematic roundabouts are the 2x2 multi-lane ones that have been cited so prevalently throughout this thread.  Should we ignore the Carmel roundabouts with high crash rates just because most of the roundabouts in the city work well?    There are lessons to be learned from these high crash rate roundabouts.

The generic roundabout safety statistics should maybe read like this…

-40% reduction in total crashes….
-80% reduction in injury crashes…
-90% reduction in fatal crashes…..
 
*except for 2x2 multi-lane roundabouts.  These will see a significant increase in total crashes and the reduction in injury crashes will be questionable at best.  Signage and pavement marking tweaks will be made to the roundabout in a vain attempt to reduce the high crash rate.  Engineers, perplexed with why there are so many crashes, will eventually say “screw it” and eliminate circulating lanes inside the roundabout as a last ditch effort to reduce the high crash rate.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on October 26, 2015, 03:17:49 PM
Can you please analyze some of Washington's roundabouts? As usual, I have no idea where to find those AADT numbers, nor the crash rates. I know back on the first or second page, you pulled some numbers for some roundabouts in Washingotn, but the numbers were over a decade old, and I'm interested to see whether or not any new developments have occurred since then.

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/BellinghamRB_zps3pdtzhyx.png)

Here’s one that hasn’t been discussed yet.  In 2002, the City of Bellingham constructed a roundabout at the intersection of Cordata Parkway & Kellogg Road near Whatcom Community College.  In 2008, after 6 years of operation, the roundabout had the highest accident rate in Bellingham with 17 total crashes.  In 2009 there were 18 crashes.  According to the Whatcom County traffic counts, the roundabout has an AADT of 15,200.  This equates to a crash rate of 3.15.

http://wcog.org/wp-content/uploads/documents/2012TrafficCountManual.pdf
http://www.whatcomhorizon.com/2010/04/roundabout-confusion/
Title: Re: Crash prone 'modern roundabouts'
Post by: ScottRAB on October 26, 2015, 03:43:49 PM
The one at US-101/OR-202 in Astoria has, over the long term, resulted in a 150% increase in crashes, without any reduction in accident severity

Even worse is the one at MLK Pkwy, Pioneer Parkway, and Hayden Bridge Way in Springfield.  It cost almost $10 million to build, and it had almost 200 accidents between 2009 and 2013, with volumes only running 15,000-20,000 ADT. 

Can you provide us a reference for your data?  One we can independently verify?
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on October 28, 2015, 01:12:56 PM
The one at US-101/OR-202 in Astoria has, over the long term, resulted in a 150% increase in crashes, without any reduction in accident severity

Even worse is the one at MLK Pkwy, Pioneer Parkway, and Hayden Bridge Way in Springfield.  It cost almost $10 million to build, and it had almost 200 accidents between 2009 and 2013, with volumes only running 15,000-20,000 ADT. 

Can you provide us a reference for your data?  One we can independently verify?

According to a City of Springfield report, the multi-lane roundabout at MLK Parkway & Hayden Bridge Way had a crash rate of 2.91; nearly 3x higher than the next crash rate intersection in the city.  Refer to pages 30-32:

(http://alexforfg.com/wp-content/uploads/2014/12/springfieldtsp.jpg)
http://www.centrallanertsp.org/sites/default/files/Volume%203,%20Appendix%20B,%2001.09.14-web_0.pdf

Oregon's crash data system can be found in the link below if you want to independently verify the crashes that are occurring. 
https://zigzag.odot.state.or.us/uniquesig08615cf883bed667d26bcec3a7dc5c6b/uniquesig0/SecurezigzagPortalHomePage/
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on October 30, 2015, 02:10:55 AM
Here’s a list of multi-lane roundabouts sorted by crash rate.  Most of the roundabouts on this list have already been discussed and the data can be verified digging through the links in this thread.  Rows highlighted in yellow have had circulating lanes removed in an attempt to address the high crash rate.  The average crash rate at signalized intersections is about 0.8 MEV.  The crash rate at these multi-lane roundabouts exceeds the average crash rate at signalized intersections by a big margin.

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/crashrate_zpsglb8qh4x.png)

Not all multi-lane roundabouts have high crash rates.  In the graph below, the 2x1 roundabouts have low crash rates while the 2x2 roundabouts have high crash rates. The exception is the 2x1 roundabout at Diffley & Rahn.  This roundabout has a central island diameter of 80’ which is the smallest CID of any of the Minnesota roundabouts analyzed.  It’s my belief that if a roundabout is too small, drivers have difficulty judging gaps to safely enter the roundabout.  The small CID may be a plausible reason why the 2x1 roundabout at Diffley & Rahn has a high crash rate.

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/MNrbs_zpsx3wr39yq.png)
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on October 30, 2015, 12:11:01 PM
The one at US-101/OR-202 in Astoria has, over the long term, resulted in a 150% increase in crashes, without any reduction in accident severity

Even worse is the one at MLK Pkwy, Pioneer Parkway, and Hayden Bridge Way in Springfield.  It cost almost $10 million to build, and it had almost 200 accidents between 2009 and 2013, with volumes only running 15,000-20,000 ADT. 

Can you provide us a reference for your data?  One we can independently verify?

ScottRAB, what's your take on these 2x2 multi-lane roundabouts?  The generic safety stats say there will be a 40% drop in total crashes but that's not what we are seeing with these multi-lane roundabouts.  More concerning, several of the 2x2 multi-lane roundabouts have seen injury accidents increase. 
Title: Re: Crash prone 'modern roundabouts'
Post by: Tarkus on November 02, 2015, 08:50:00 PM
The one at US-101/OR-202 in Astoria has, over the long term, resulted in a 150% increase in crashes, without any reduction in accident severity

Even worse is the one at MLK Pkwy, Pioneer Parkway, and Hayden Bridge Way in Springfield.  It cost almost $10 million to build, and it had almost 200 accidents between 2009 and 2013, with volumes only running 15,000-20,000 ADT. 

Can you provide us a reference for your data?  One we can independently verify?

These are taken directly from ODOT's crash reporting system.  Plugging in the same dates, the data is replicable.

Here's all the source data from US-101/OR-202 Astoria.  The Pre-Roundabout Period runs from 10/1/1993 to 09/30/2002, while the Post-Roundabout Period runs 10/1/2002 to 09/30/2011.

Astoria Pre-Roundabout KABCO (http://alexforfg.com/wp-content/uploads/2014/10/Astoria-PreRoundabout-KABCO.pdf)
Astoria Pre-Roundabout Comprehensive (http://alexforfg.com/wp-content/uploads/2014/10/Astoria-PreRoundabout-Comp.pdf)
Astoria Pre-Roundabout Truck Included (http://alexforfg.com/wp-content/uploads/2014/10/Astoria-Roundabout-TruckIncluded.pdf)
Astoria Post-Roundabout KABCO (http://alexforfg.com/wp-content/uploads/2014/10/Astoria-Roundabout-KABCO.pdf)
Astoria Post-Roundabout Comprehensive (http://alexforfg.com/wp-content/uploads/2014/10/Astoria-Roundabout-Comp.pdf)
Astoria Post-Roundabout Truck Included (http://alexforfg.com/wp-content/uploads/2014/10/Astoria-PreRoundabout-TruckIncluded.pdf)

The data showing over 180 crashes between 2009 and 2013 at the Springfield Pioneer/MLK/Hayden Bridge roundabout is below.  Because there's multiple road names involved, ODOT has the data divided by approach, requiring one to add everything up to get the full picture.

Pioneer Pkwy W and Hayden Bridge KABCO (http://alexforfg.com/wp-content/uploads/2014/12/Pioneer-Pkwy-W-and-Hayden-Bridge-KABCO.pdf)
Pioneer Pkwy E and Hayden Bridge KABCO (http://alexforfg.com/wp-content/uploads/2014/12/Pioneer-Pkwy-E-and-Hayden-Bridge-KABCO.pdf)
MLK and Hayden Bridge KABCO (http://alexforfg.com/wp-content/uploads/2014/12/MLK-and-Hayden-Bridge-KABCO.pdf)

Neither Springfield nor Lane County has good volume data on the intersection beyond the earlier Springfield TSP figures.  The most recent Springfield data is from 2008 (http://www.ci.springfield.or.us/pubworks/transportation/Images/Maps/ADT_MAP_2008%2011%20x%2017%20%281%29.pdf) and only shows the approaches.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on November 03, 2015, 11:28:45 AM
Some 2x2 multi-lane roundabouts were constructed along Shiloh Rd in Billings, Montana in 2010.  According to the Billings Police Department, the roundabout at Shiloh & Grand is currently the 8th most dangerous intersection in the city and the roundabout at Shiloh & King is the 4th most dangerous intersection in the city. 

http://billingsgazette.com/news/local/crime-and-courts/crime-stats-billings-most-dangerous-intersections/collection_97fee293-e4d2-5dac-8854-ceb50a22f030.html


Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on November 03, 2015, 12:48:02 PM
Here’s an interesting case study.  Pre-2008 Cony Circle in Augusta, Maine averaged over 100 crashes per year and was the highest crash rate intersection in the state.  In 2008, the circle was reconfigured with modern roundabout standards.  After the conversion accidents dropped by 50%.  That may sound impressive, but as of 2014 the roundabout has a crash rate of 11.87 and is still the 3rd highest crash location in Maine.  Is that really a victory?  It’s similar to an 800 pound person losing 50% of their body weight.  They are still morbidly obese. 

http://www.centralmaine.com/2011/08/11/cony-circle-accidents-down_2011-08-10/
http://www.wgme.com/images/DANGEROUS%20ROADWAY%20INTERSECTIONS.pdf

Cony Circle:  Pre-2008
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/08-Untitled_zpshnpikktf.png)

Cony Circle:  Post-2008
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/15Untitled_zpsl7d1abyq.png)

Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on November 03, 2015, 02:25:05 PM
Some 2x2 multi-lane roundabouts were constructed along Shiloh Rd in Billings, Montana in 2010.  According to the Billings Police Department, the roundabout at Shiloh & Grand is currently the 8th most dangerous intersection in the city and the roundabout at Shiloh & King is the 4th most dangerous intersection in the city. 

http://billingsgazette.com/news/local/crime-and-courts/crime-stats-billings-most-dangerous-intersections/collection_97fee293-e4d2-5dac-8854-ceb50a22f030.html

Any idea why the most dangerous intersections are signals?

Here’s an interesting case study.  Pre-2008 Cony Circle in Augusta, Maine averaged over 100 crashes per year and was the highest crash rate intersection in the state.  In 2008, the circle was reconfigured with modern roundabout standards.  After the conversion accidents dropped by 50%.  That may sound impressive, but as of 2014 the roundabout has a crash rate of 11.87 and is still the 3rd highest crash location in Maine.  Is that really a victory?  It’s similar to an 800 pound person losing 50% of their body weight.  They are still morbidly obese.

I'm not sure there are any other effective ways to intersect five roads that wouldn't cause outrageous congestion.

What are the top two intersections?

Here’s one that hasn’t been discussed yet.  In 2002, the City of Bellingham constructed a roundabout at the intersection of Cordata Parkway & Kellogg Road near Whatcom Community College.  In 2008, after 6 years of operation, the roundabout had the highest accident rate in Bellingham with 17 total crashes.  In 2009 there were 18 crashes.  According to the Whatcom County traffic counts, the roundabout has an AADT of 15,200.  This equates to a crash rate of 3.15.
http://www.whatcomhorizon.com/2010/04/roundabout-confusion/

This got me thinking:

Is the crash rate an effective means of studying intersection safety? By your measure, the roundabout featured here would be considered dangerous, but that's only because of the "3.15" number. In real life, 17 or 18 collisions just isn't that many (that's one every three weeks, give or take, and there's no telling how severe the collisions were). An intersection with an AADT of 50,000 with a crash rate of 3.15 would have fewer collisions per number of cars entering, but still way more collisions than 17 or 18 a year.

Now, if that's okay simply because more cars = more collisions, that's been my point all along. Multi-lane roundabouts are, obviously, capable of handling far more cars than single-lane roundabouts, simply because there are more circulating lanes, thus more cars in the intersection at any given point capable of whacking into each other. Considering that, I propose that three lane roundabouts are no more dangerous than two or one lane roundabouts. They just handle an enormous amount of cars relative to the smaller roundabouts, so they appear to be much more dangerous. If a traffic engineers' only method of making an intersection safer is by reducing the theoretical through-put of an intersection, simply to lessen the chances of a collision by decreasing the amount of cars in the intersection that could theoretically collide, you're not solving any problems. That's just a trade-off.

Now, I could be looking at this all wrong. I am, after all, not a traffic engineer, nor an expert in analyzing data.

As well (perhaps unrelated), please don't compare roundabouts with Michigan Lefts, as you have before. I love Michigan Lefts just as much as the next person, but the ROW required to install them is usually far more than most agencies can provide. I don't find see them in the same category as roundabouts or traditional signals (they're more like freeways -- a series of intersections working in tandem to filter traffic along a central artery).
Title: Re: Crash prone 'modern roundabouts'
Post by: Tarkus on November 03, 2015, 03:16:02 PM
I'm not sure there are any other effective ways to intersect five roads that wouldn't cause outrageous congestion.

I'll be upfront and say I'm typically not a fan of roundabouts, for various reasons, but one of the places they do make sense is situations with unusual geometry, that would be messy with a more "conventional" treatment.  There's one caveat to the particular Maine intersection being mentioned, however, that I'll note later.

Here’s one that hasn’t been discussed yet.  In 2002, the City of Bellingham constructed a roundabout at the intersection of Cordata Parkway & Kellogg Road near Whatcom Community College.  In 2008, after 6 years of operation, the roundabout had the highest accident rate in Bellingham with 17 total crashes.  In 2009 there were 18 crashes.  According to the Whatcom County traffic counts, the roundabout has an AADT of 15,200.  This equates to a crash rate of 3.15.
http://www.whatcomhorizon.com/2010/04/roundabout-confusion/

Now, if that's okay simply because more cars = more collisions, that's been my point all along. Multi-lane roundabouts are, obviously, capable of handling far more cars than single-lane roundabouts, simply because there are more circulating lanes, thus more cars in the intersection at any given point capable of whacking into each other. Considering that, I propose that three lane roundabouts are no more dangerous than two or one lane roundabouts. They just handle an enormous amount of cars relative to the smaller roundabouts, so they appear to be much more dangerous. If a traffic engineers' only method of making an intersection safer is by reducing the theoretical through-put of an intersection, simply to lessen the chances of a collision by decreasing the amount of cars in the intersection that could theoretically collide, you're not solving any problems. That's just a trade-off.

Now, I could be looking at this all wrong. I am, after all, not a traffic engineer, nor an expert in analyzing data.

The MEV abbreviation that tradephoric and others have used in this thread stands for "per million entering vehicles".  In short It's actually a way of getting a crash rate that is not dependent on the actual traffic volume, and allows engineers to better compare intersections.  An intersection with a crash rate of 3.15 per MEV need not necessarily have a higher volume of traffic than one with a rate of 0.90 per MEV, but it does mean statistically that the 3.15 per MEV intersection is going to be a bit more than three times as crash prone.

All these high MEV ratings for multi-lane roundabouts are essentially showing that once you get beyond 1x1 or 2x1 roundabouts, into roundabout treatments for higher-volume situations, the safety benefits quickly become null and void.  Cost also becomes a factor--the MLK/Hayden Bridge roundabout in Springfield cost over $9 million to construct.
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on November 03, 2015, 03:24:18 PM
The MEV abbreviation that tradephoric and others have used in this thread stands for "per million entering vehicles".  In short It's actually a way of getting a crash rate that is not dependent on the actual traffic volume, and allows engineers to better compare intersections.  An intersection with a crash rate of 3.15 per MEV need not necessarily have a higher volume of traffic than one with a rate of 0.90 per MEV, but it does mean statistically that the 3.15 per MEV intersection is going to be a bit more than three times as crash prone.

Thank you for clarifying that. I had a feeling I was missing a piece of the puzzle.
Title: Re: Crash prone 'modern roundabouts'
Post by: lordsutch on November 03, 2015, 03:39:13 PM
All these high MEV ratings for multi-lane roundabouts are essentially showing that once you get beyond 1x1 or 2x1 roundabouts, into roundabout treatments for higher-volume situations, the safety benefits quickly become null and void.  Cost also becomes a factor--the MLK/Hayden Bridge roundabout in Springfield cost over $9 million to construct.

The overall crash rate benefits may be "null and void," but these high volume intersections that require a multilane solution are the ones that lead to the vast majority of fatality crashes when they're signalized or have multi-way stop conditions. Without getting into the weeds of cost-benefit analysis,* a few more (or even many more) fender benders and whiplash accidents are massively preferable to a few more deaths from people being T-boned by red-light runners and the like.

* If we take the value of a human life at somewhere between $8-10 million (https://www.transportation.gov/sites/dot.gov/files/docs/VSL_Guidance_2014.pdf), even several hundred more accidents at $5-10k a pop would be "worth" it.
Title: Re: Crash prone 'modern roundabouts'
Post by: Tarkus on November 03, 2015, 06:29:35 PM
Without getting into the weeds of cost-benefit analysis,* a few more (or even many more) fender benders and whiplash accidents are massively preferable to a few more deaths from people being T-boned by red-light runners and the like.

In theory, yes--signalized intersections aren't "childproofed" with all those rounded edges, allowing the potential for those types of angle crashes--though theory and the actual real-world results don't always correlate, and that's one of the main arguments being discussed in this thread.  Many of the cases cited in this thread, where multi-lane roundabouts have replaced signals, have shown increases in injury accidents as well as total accidents, even over the longer term.  Curiously, I've yet to see a comparison involving a fatality on either side (pre- or post-multi-lane roundabout), however.
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on November 03, 2015, 07:06:14 PM
Without getting into the weeds of cost-benefit analysis,* a few more (or even many more) fender benders and whiplash accidents are massively preferable to a few more deaths from people being T-boned by red-light runners and the like.

In theory, yes--signalized intersections aren't "childproofed" with all those rounded edges, allowing the potential for those types of angle crashes--though theory and the actual real-world results don't always correlate, and that's one of the main arguments being discussed in this thread.  Many of the cases cited in this thread, where multi-lane roundabouts have replaced signals, have shown increases in injury accidents as well as total accidents, even over the longer term.  Curiously, I've yet to see a comparison involving a fatality on either side (pre- or post-multi-lane roundabout), however.

It's a matter of high-speed impacts vs low-speed impacts. There can be injuries in both, of course, but it's more like whiplash vs broken back, or bump on the head vs broken legs. Unfortunately for us, both injuries get lumped together, even though 100% of people would prefer the former two over the latter two.

Carmel, Indiana, according to their mayor Jim Brainard, does not have a full Jaws of Life in their city because they don't really have severe collisions anymore (this was on the last page):

http://wishtv.com/2015/10/08/roundabouts-may-confuse-but-stats-back-up-their-safety/

Quote
And even if you make a mistake, because speeds are so slow, most wrecks don’t involve serious injuries....[Carmel Mayor Jim Brainard] points out that because accidents and injuries are down in Carmel, insurance rates have dropped. He says the city doesn’t have a full “jaws of life” crew in its fire department anymore because they don’t have the high speed impacts that they used to have and don’t need them very often.

The issue that tradephoric likes to bring up is negligence. He states repeatedly that cities can be found negligent if they knowingly do nothing about intersections that have high crash rates. I would agree that there could be a negligence issue. The problem is that A) no one political body has power over a city's engineering department, thus there's no one that could single-handily bar any further roundabout construction, or more importantly B) while a citizen could privately sue the city for negligence after receiving a minor injury in the roundabout, any city which has invested millions of dollars into roundabouts would go to huge lengths to protect their investments in court, by providing evidence to a judge and jury, demonstrating that while there may be more collisions, the roundabouts are actually safer (in terms of both fatalities and severe injuries).
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on November 03, 2015, 10:47:31 PM
It's a matter of high-speed impacts vs low-speed impacts. There can be injuries in both, of course, but it's more like whiplash vs broken back, or bump on the head vs broken legs. Unfortunately for us, both injuries get lumped together, even though 100% of people would prefer the former two over the latter two.

There is a rating system known as FARS (Fatality Analysis Reporting System) that is used to code injury accidents by severity.  Here’s a breakdown of the rating system:

Quote
0 No Injury (O)
1 Possible Injury (C)
2 Non-incapacitating Evident Injury (B)
3 Incapacitating Injury (A)
4 Fatal Injury (K)
5 Injured, Severity Unknown
6 Died Prior to Accident*
9 Unknown

Code 1 (Possible Injury). A possible injury is any injury reported or claimed which is not a fatal injury, incapacitating injury or non-incapacitating evident injury. This includes: momentary unconsciousness, claim of injuries not evident, limping, complaint of pain, nausea and hysteria.

Code 2 (Non-incapacitating Evident Injury). A non-incapacitating evident injury is any injury, other than a fatal injury or an incapacitating injury, which is evident to observers at the scene of the accident in which the injury occurred. This includes: lump on head, abrasions, bruises and minor lacerations. This does not include limping (the injury cannot be seen). (See code “1”).

Code 3 (Incapacitating Injury). An incapacitating injury is any injury, other than a fatal injury, which prevents the injured person from walking, driving or normally continuing the activities the person was capable of performing before the injury occurred. This includes: severe lacerations, broken or distorted limbs, skull or chest injuries, abdominal injuries, unconsciousness at or when taken from the accident scene, and unable to leave the accident scene without assistance. This does not include momentary unconsciousness. (See code “1”).

Code 4 (Fatal Injury), must only be used if the death occurred within thirty 24-hour time periods from the time of the accident. Every effort should be made to determine that the Death Date was within thirty 24-hour time periods from the Accident Time.

Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on November 03, 2015, 11:14:31 PM
It's a matter of high-speed impacts vs low-speed impacts. There can be injuries in both, of course, but it's more like whiplash vs broken back, or bump on the head vs broken legs. Unfortunately for us, both injuries get lumped together, even though 100% of people would prefer the former two over the latter two.

There is a rating system known as FARS (Fatality Analysis Reporting System) that is used to code injury accidents by severity.  Here’s a breakdown of the rating system:

Thank you for posting that. I figured there might be something, but I hadn't heard of anything until now. How often is crash data compiled with FARS' numbers?
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on November 04, 2015, 12:13:22 AM
Thank you for posting that. I figured there might be something, but I hadn't heard of anything until now. How often is crash data compiled with FARS' numbers?

In Michigan, the FARS code is compiled for every reported traffic crash in the state.  Law enforcement agencies are required to complete a UD-10 which includes the FARS code.  Below is a link to a sample UD-10 which shows injury severity ranging from no injury (Unit 1 driver) to A-level injury (Unit 1 passenger):

http://semcog.org/Data-and-Maps/Crash-and-Road-Data/Crash_Id/8338533/view/UD10CrashReport

Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on November 04, 2015, 12:15:37 PM
The overall crash rate benefits may be "null and void," but these high volume intersections that require a multilane solution are the ones that lead to the vast majority of fatality crashes when they're signalized or have multi-way stop conditions. Without getting into the weeds of cost-benefit analysis,* a few more (or even many more) fender benders and whiplash accidents are massively preferable to a few more deaths from people being T-boned by red-light runners and the like.

* If we take the value of a human life at somewhere between $8-10 million (https://www.transportation.gov/sites/dot.gov/files/docs/VSL_Guidance_2014.pdf), even several hundred more accidents at $5-10k a pop would be "worth" it.

Compare the 2014 traffic fatalities that occurred in Sterling Heights, MI and Carmel, IN.  Sterling Heights has a population of 130,410 and Carmel has a population of 85,927.  Both communities experienced 2 fatal crashes in 2014 (based on google searches and UD-10 forms).  Ironically, the two fatal crashes that occurred in Carmel happened inside roundabouts.  Neither fatality in Sterling Heights occurred at an intersection (according to the UD-10 forms).  Keep in mind, Sterling Heights has a population nearly 45k higher than Carmel.   I thought roundabouts reduce fatal crashes by 90%.  How then did Sterling Heights, a city full of traffic signals, have zero fatal intersection crashes while Carmel, a city full of roundabouts,  have 2 fatal roundabout crashes?

Fatal crashes in Carmel:
http://fox59.com/2014/08/06/one-dead-in-carmel-accident-passenger-taken-to-hospital/
http://fox59.com/2014/09/26/person-dead-after-motorcycle-accident-in-carmel/

Fatal crashes in Sterling Heights:
http://semcog.org/Data-and-Maps/Crash-and-Road-Data/Crash_Id/8939474/view/UD10CrashReport
http://semcog.org/Data-and-Maps/Crash-and-Road-Data/Crash_Id/8986238/view/UD10CrashReport
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on November 04, 2015, 08:19:46 PM
The overall crash rate benefits may be "null and void," but these high volume intersections that require a multilane solution are the ones that lead to the vast majority of fatality crashes when they're signalized or have multi-way stop conditions. Without getting into the weeds of cost-benefit analysis,* a few more (or even many more) fender benders and whiplash accidents are massively preferable to a few more deaths from people being T-boned by red-light runners and the like.

* If we take the value of a human life at somewhere between $8-10 million (https://www.transportation.gov/sites/dot.gov/files/docs/VSL_Guidance_2014.pdf), even several hundred more accidents at $5-10k a pop would be "worth" it.

Compare the 2014 traffic fatalities that occurred in Sterling Heights, MI and Carmel, IN.  Sterling Heights has a population of 130,410 and Carmel has a population of 85,927.  Both communities experienced 2 fatal crashes in 2014 (based on google searches and UD-10 forms).  Ironically, the two fatal crashes that occurred in Carmel happened inside roundabouts.  Neither fatality in Sterling Heights occurred at an intersection (according to the UD-10 forms).  Keep in mind, Sterling Heights has a population nearly 45k higher than Carmel.   I thought roundabouts reduce fatal crashes by 90%.  How then did Sterling Heights, a city full of traffic signals, have zero fatal intersection crashes while Carmel, a city full of roundabouts,  have 2 fatal roundabout crashes?

Fatal crashes in Carmel:
http://fox59.com/2014/08/06/one-dead-in-carmel-accident-passenger-taken-to-hospital/
http://fox59.com/2014/09/26/person-dead-after-motorcycle-accident-in-carmel/

Fatal crashes in Sterling Heights:
http://semcog.org/Data-and-Maps/Crash-and-Road-Data/Crash_Id/8939474/view/UD10CrashReport
http://semcog.org/Data-and-Maps/Crash-and-Road-Data/Crash_Id/8986238/view/UD10CrashReport

Because stats vary between cities? Aren't you a traffic engineer? Anomalies are perfectly common. This is obviously the 10% (though, keep reading...)

The whole point of this thread was to compile data for hundreds of roundabouts to prove a point that multi-lane roundabouts have more collisions. You have done a great job illustrating this, and I am definitely a believer at this point. There is no doubt that multi-lane roundabouts have more collisions (at this point, it's just a matter of whether or not that's a big deal).

You do lose me, however, when you attempt to prove that roundabouts are deadlier than signals by grabbing random data from two random cities, over random time frames. You're one step away from generalizing roundabouts as being deadlier than signals. And that's obviously nuts...right? It doesn't take a genius to figure out that roundabouts, just by the very nature of their design, are safer than signals (taking into account FARS data).

Intersections should be designed to minimize risk. Stats show that, in almost all cases, roundabouts may have more collisions, but are far safer for the driver. There are going to be isolated incidents of drivers not paying attention to the circle ahead, and lose control. It's just a fact. The place where roundabouts succeed is by reducing the potential for dangerous two-party collisions like you might see at signals. Drivers can lose control anywhere along a road (including at signals) and kill themselves. That shouldn't be a strike against the roundabout.
Title: Re: Crash prone 'modern roundabouts'
Post by: lordsutch on November 05, 2015, 12:23:40 AM
The fundamental issue in this thread as I see it is that there is a wealth of scientific studies completed and in-process on the safety impacts of roundabouts, in the United States and elsewhere. I found dozens with a cursory Google Scholar search.

At this point I'd say either you need to do a systematic study of publishable caliber to demonstrate that the existing studies are wrong and that multilane roundabouts are really deathtraps, despite the accumulating mountain of evidence to the contrary produced by transportation research professionals around the world, or this thread has run its course.

And by "systematic study," I don't mean cherry-picked data from one year from a couple of cities. I mean a statistical analysis of a large volume of data, using a proper sample and appropriate control variables.
Title: Re: Crash prone 'modern roundabouts'
Post by: Rothman on November 05, 2015, 08:57:04 AM
The fundamental issue in this thread as I see it is that there is a wealth of scientific studies completed and in-process on the safety impacts of roundabouts, in the United States and elsewhere. I found dozens with a cursory Google Scholar search.

At this point I'd say either you need to do a systematic study of publishable caliber to demonstrate that the existing studies are wrong and that multilane roundabouts are really deathtraps, despite the accumulating mountain of evidence to the contrary produced by transportation research professionals around the world, or this thread has run its course.

And by "systematic study," I don't mean cherry-picked data from one year from a couple of cities. I mean a statistical analysis of a large volume of data, using a proper sample and appropriate control variables.

 :clap: :clap: :clap:
Title: Re: Crash prone 'modern roundabouts'
Post by: DaBigE on November 05, 2015, 09:06:43 AM
The fundamental issue in this thread as I see it is that there is a wealth of scientific studies completed and in-process on the safety impacts of roundabouts, in the United States and elsewhere. I found dozens with a cursory Google Scholar search.

At this point I'd say either you need to do a systematic study of publishable caliber to demonstrate that the existing studies are wrong and that multilane roundabouts are really deathtraps, despite the accumulating mountain of evidence to the contrary produced by transportation research professionals around the world, or this thread has run its course.

And by "systematic study," I don't mean cherry-picked data from one year from a couple of cities. I mean a statistical analysis of a large volume of data, using a proper sample and appropriate control variables.

I said nearly the same thing several pages/months ago. Interesting to see this thread still going in circles (pun intended).
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on November 05, 2015, 10:44:40 AM
This thread has been focused on 2x2 multi-lane roundabouts.  These 2x2 roundabouts are the ones experiencing high crash rates.  Citing studies skewed towards single-lane and 2x1 multi-lane roundabouts don’t reveal the safety performance of 2x2 multi-lane roundabouts.  Find a study that focuses on the safety benefits of 2x2 multi-lane roundabouts and then we can talk.  Of course this point has already been made but some fail to recognize it:

The Insurance Institute for Highway Safety released a report in 2000 evaluating the safety of 24 intersections that were converted to roundabouts.  The report found the following:

Quote
The present study evaluated changes in motor vehicle crashes following conversion of 24 intersections from stop sign and traffic signal control to modern roundabouts. The settings, located in 8 states, were a mix of urban, suburban, and rural environments. A before-after study was conducted using the empirical Bayes approach, which accounts for regression to the mean. Overall, the empirical Bayes procedure estimated highly significant reductions of 39 percent for all crash severities combined and 76 percent for all injury crashes. Reductions in the numbers of fatal and incapacitating injury crashes were estimated to be about 90 percent.

http://safety.fhwa.dot.gov/intersection/resources/fhwasa09027/resources/Crash%20Reductions%20Following%20Installation%20of%20Roundabouts.pdf

The study was skewed towards evaluating single-lane roundabouts as only 9 of the 24 intersections evaluated were multi-lane roundabouts.  The 9 multi-lane roundabouts evaluated were all from Colorado and 6 of the 9 serviced interchanges along I-70.  The 3 non-interchange multi-lane roundabouts evaluated in the study were all along Avon Road in Avon, Colorado. When looking at aerials, there appears to be limited traffic generated along the side-street for 2 of the 3 roundabouts (IE. the side-street isn’t a major route).  Here is a list of all the roundabouts evaluated in the Insurance Institute study:

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/2000study_zpsvmsggp6l.png)

In the press release for the proposed multi-lane roundabout at State & Ellsworth, the Washtenaw County Road Commission cited a study with familiar looking safety numbers:

Quote
As stated by a 2011 report from the Insurance Institute of Highway Safety, 23 intersections that were converted into roundabouts experienced significant declines in accidents. Total crash frequency fell by approximately 40 percent; injury crash frequency fell by approximately 80 percent; and fatal crash frequency fell by approximately 90 percent.

http://www.wcroads.org/node/529

Citing a study that is skewed towards single-lane roundabouts when a major multi-lane roundabout is being proposed seems disingenuous.  Even the multi-lane roundabouts evaluated in the 2000 study are dissimilar to the roundabout that was being proposed for State & Ellsworth.  In the first year of operation, State & Ellsworth experienced roughly a 10x increase in crashes (not a 40% reduction).  Agencies shouldn't be implying that large multi-lane roundabouts will see a reduction in total crashes (and by citing studies that are skewed towards single-lane roundabouts, that's exactly what they are doing).


Title: Re: Crash prone 'modern roundabouts'
Post by: lordsutch on November 05, 2015, 01:12:22 PM
This thread has been focused on 2x2 multi-lane roundabouts.  These 2x2 roundabouts are the ones experiencing high crash rates.  Citing studies skewed towards single-lane and 2x1 multi-lane roundabouts don’t reveal the safety performance of 2x2 multi-lane roundabouts.  Find a study that focuses on the safety benefits of 2x2 multi-lane roundabouts and then we can talk.  Of course this point has already been made but some fail to recognize it:

No, the point is that the burden of proof that 2x2 multi-lane roundabouts are inherently unsafe is on you. You have not demonstrated this using evidence that would be accepted by the transportation research community, using a systematic study (not "I found another 2x2 roundabout with a few crashes").

Not to mention you keep moving the goalposts on this thread. First it was all modern roundabouts were deathtraps (which was demonstrated to be false). Then it was all multi-lane roundabouts are deathtraps, regardless of the lanes on each leg (ditto). Now it's all multi-lane roundabouts that have 2 or more lanes on each entering leg are deathtraps (where it's apparently "Carmel had 2 fatality accidents in roundabouts in 2014, so nyeh!").
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on November 05, 2015, 03:00:54 PM
No, the point is that the burden of proof that 2x2 multi-lane roundabouts are inherently unsafe is on you. You have not demonstrated this using evidence that would be accepted by the transportation research community, using a systematic study (not "I found another 2x2 roundabout with a few crashes").

Take a look at the 2x2 roundabouts that have been included in these published studies and see how they have performed.  A 2011 roundabout study funded by the Wisconsin Department of Transportation was cited previously on this thread.  Of the 24 roundabouts analyzed, there was only one 2x2 multi-lane roundabout (STH 32/ STH 57 Broadway in De Pere).   According to the study, 11 of the roundabouts had increases in crashes.  Here’s an excerpt from the study found on page 23:

Quote
Among the 11 locations with increased crash record, STH 32/STH 57 Broadway, Canal St/25th Ave, Thompson and Commercial, contribute 38 percent, 15 percent and 18 percent of all increases in the total number of crashes, respectively. All combined, the three locations contribute 71 percent of the crash increases.
http://www.topslab.wisc.edu/programs/safety/projects/roundabouts/WI%20Roundabout%20Evaluation%20Volume%202%20Safety.pdf

The 2x2 multi-lane roundabout analyzed in the Wisconsin study (Sth 32/STH 57 Broadway) accounted for 38% of the crash increases in the study.  Put another way, if this 2x2 roundabout hadn't been included in the study, the Wisconsin safety numbers would have looked a lot better.  Shortly after the release of the study, a circulating lane inside the 32/57 roundabout was removed.  They waved the white flag and converted it to a 2x1 roundabout to address the high crash rate.

Not to mention you keep moving the goalposts on this thread. First it was all modern roundabouts were deathtraps (which was demonstrated to be false). Then it was all multi-lane roundabouts are deathtraps, regardless of the lanes on each leg (ditto). Now it's all multi-lane roundabouts that have 2 or more lanes on each entering leg are deathtraps (where it's apparently "Carmel had 2 fatality accidents in roundabouts in 2014, so nyeh!").

Quote where i said this.  Fair enough? 
Title: Re: Crash prone 'modern roundabouts'
Post by: DaBigE on November 05, 2015, 04:22:44 PM
Quote
Among the 11 locations with increased crash record, STH 32/STH 57 Broadway, Canal St/25th Ave, Thompson and Commercial, contribute 38 percent, 15 percent and 18 percent of all increases in the total number of crashes, respectively. All combined, the three locations contribute 71 percent of the crash increases.
http://www.topslab.wisc.edu/programs/safety/projects/roundabouts/WI%20Roundabout%20Evaluation%20Volume%202%20Safety.pdf

The 2x2 multi-lane roundabout analyzed in the Wisconsin study (Sth 32/STH 57 Broadway) accounted for 38% of the crash increases in the study.  Put another way, if this 2x2 roundabout hadn't been included in the study, the Wisconsin safety numbers would have looked a lot better.  Shortly after the release of the study, a circulating lane inside the 32/57 roundabout was removed.  They waved the white flag and converted it to a 2x1 roundabout to address the high crash rate.

To be fair, it wasn't just the crash rate they were addressing. They were also addressing queuing and delays that developed counter to the pre-construction forecasts. It could also be said that the queuing had a part in the increase in crashes...the longer you're waiting, the more risks/smaller gaps you'll try and take.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on November 06, 2015, 12:31:47 AM
After two months of operation, a double-lane roundabout in Lakeville, Minnesota has tallied up 44 crashes.  Traffic counts at the roundabout are about 30,000 vehicles per day.  This equates to a crash rate of 24.1 MEV.  The crash rate should drop as drivers become more familiar with the roundabout - but even still - this is a horrible initial result.  It will be interesting to track the crashes over time at this roundabout. 

(http://sunthisweek.com/wp-content/uploads/sites/23/2015/08/image.jpg)
http://sunthisweek.com/2015/11/05/number-of-lakeville-roundabout-accidents-drop/?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+Thisweeklivecom+%28ThisweekLive.com%29
Title: Re: Crash prone 'modern roundabouts'
Post by: Tom958 on November 06, 2015, 07:22:55 AM
...produced by transportation research professionals around the world...

That's what I want to know: is this questionable accident experience inherent to roundabouts in general, or is it an American thing? As I understand it, roundabouts were invented and first built in the UK, then spread to other places after their advantages had been proven through years of experience. They didn't make it over here until the third or fourth wave, at which point the accumulated evidence made it increasingly indefensible not to adopt them. If said evidence was a hoax (!), then we've got a concrete (and asphalt) problem. But if it's a matter of somehow inducing Americans to drive like other people... it's just a software issue.  :D

Title: Re: Crash prone 'modern roundabouts'
Post by: DaBigE on November 06, 2015, 01:02:26 PM
New story regarding the Lakeville, MN roundabout: http://bringmethenews.com/2015/11/05/lakeville-drivers-are-starting-to-get-used-to-the-roundabout/ (http://bringmethenews.com/2015/11/05/lakeville-drivers-are-starting-to-get-used-to-the-roundabout/)

Quote
The newspaper says following its opening, there were 28 accidents on the roundabout in September, according to Lakeville Police Chief Jeff Long. However, this number dropped to 16 in October.

Quote
After it opened, the Minnesota Department of Transportation said most of the accidents occur on roundabouts because people don’t yield to other vehicles when they should. And that is still a problem in Lakeville, with local Steve Bakke telling the Sun he sees drivers sometimes accelerate rather than slow down as they approach the roundabout. Nonetheless, he admitted: “Every day it’s getting better.”

Quote
It is the first multi-lane roundabout to open in Dakota County
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on November 06, 2015, 02:43:23 PM
The newspaper says following its opening, there were 28 accidents on the roundabout in September, according to Lakeville Police Chief Jeff Long. However, this number dropped to 16 in October.
If the roundabout averages 16 crashes a month, that equates to 192 crashes per year.  It’s premature to write an article with the headline “drivers are starting to get use to the roundabout” when the roundabout is on track to experience nearly 200 crashes in the first year of operation. 

After it opened, the Minnesota Department of Transportation said most of the accidents occur on roundabouts because people don’t yield to other vehicles when they should. And that is still a problem in Lakeville, with local Steve Bakke telling the Sun he sees drivers sometimes accelerate rather than slow down as they approach the roundabout. Nonetheless, he admitted: “Every day it’s getting better.”
Let’s hope it gets better every day.  It needs to get a lot better for multiple days.

It is the first multi-lane roundabout to open in Dakota County
That inaccurate.   There are several multi-lane roundabouts in Dakota County.  In fact, there is a multi-lane roundabout just two miles down the road from the new Lakeville roundabout.

https://www.google.com/maps/@44.6904743,-93.2376639,140m/data=!3m1!1e3
https://www.google.com/maps?ll=44.80465,-93.20761&z=18&t=h
https://www.google.com/maps/@44.8373943,-93.0853549,140m/data=!3m1!1e3
Title: Re: Crash prone 'modern roundabouts'
Post by: DaBigE on November 06, 2015, 03:09:18 PM
The newspaper says following its opening, there were 28 accidents on the roundabout in September, according to Lakeville Police Chief Jeff Long. However, this number dropped to 16 in October.
If the roundabout averages 16 crashes a month, that equates to 192 crashes per year.  It’s premature to write an article with the headline “drivers are starting to get use to the roundabout” when the roundabout is on track to experience nearly 200 crashes in the first year of operation.

It's also premature to make yearly crash predictions based on two months of operation, especially when a decreasing trend is beginning to appear. Given the timeframe the article was referencing, their assumption is accurate.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on November 06, 2015, 03:26:55 PM
The newspaper says following its opening, there were 28 accidents on the roundabout in September, according to Lakeville Police Chief Jeff Long. However, this number dropped to 16 in October.
If the roundabout averages 16 crashes a month, that equates to 192 crashes per year.  It’s premature to write an article with the headline “drivers are starting to get use to the roundabout” when the roundabout is on track to experience nearly 200 crashes in the first year of operation.

It's also premature to make yearly crash predictions based on two months of operation, especially when a decreasing trend is beginning to appear. Given the timeframe the article was referencing, their assumption is accurate.

Let's just wait to see if monthly crashes drop to 2 per month at this roundabout.  Even then, the roundabout would have a crash rate above 2.0 MEV. 
Title: Re: Crash prone 'modern roundabouts'
Post by: Tom958 on November 07, 2015, 10:45:39 AM
...produced by transportation research professionals around the world...

That's what I want to know: is this questionable accident experience inherent to roundabouts in general, or is it an American thing?

I found this study (https://www.scribd.com/doc/174870895/ITE-A-Comparative-Evaluation-of-the-Safety-Performance-of-Roundabouts-and-Traditional-Intersection-Controls), which compares intersections in the city of Las Vegas, and which breaks the results down by ADT into minor, medium and major intersections. In the major intersections category there are three roundabouts and three signalized intersections, with ADT ranging from 21k to 28k (which really isn't that much, is it?). It says, among other things:

"However, the roundabouts that fall into the major intersections category have more crashes than the signalized intersections. Even though the total number of crashes was more for the roundabouts, the number of injury crashes was in the same range for both roundabouts and intersections with traditional controls."

And, later in the report:

"A higher number of crashes at the roundabouts creates an impression that the signalized intersections are safer compared to roundabouts at the candidate major intersections. This contradicts the findings from Europe that the roundabouts are safer than the signals even when the daily traffic entering the roundabouts is high.." (my italics)
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on November 08, 2015, 11:59:26 AM
Thanks for the link to that Las Vegas study Tom.  Of the 3 roundabouts classified as major, only Town Center Dr. and Hualapai Way would be considered a 2x2 multi-lane roundabout.  Interestingly, this 2x2 roundabout had the worst crash rate and the worst injury crash rate of any intersection analyzed in the study (excluding stop-controlled intersections):

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/roundaboutsafetyuntitled_zpsjwq2w2rt.png)

This published study further questions the safety benefits of 2x2 multi-lane roundabouts.  There were significantly more crashes at the Town Center Dr and Hualapai Way roundabout with no reductions in injury crashes when compared to similar ADT signalized intersections in Las Vegas.  To put things into perspective, there were nearly as many injury crashes at the Town Center / Hualapai Way roundabout than total crashes at the Tenaya St / Vegas Dr. signalized intersection (3 injury crashes vs. 4.6 total crashes). 
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on November 08, 2015, 06:18:50 PM
Pretty funny when tradeph is very quick to note a high volume of accidents within a few weeks of a roundabout's opening and details how unsafe they are, but very quick to dispute someone's report of a reduction in accidents, noting that more time is needed to see the big picture.

Btw, you are still cherry-picking data.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on November 08, 2015, 06:55:45 PM
Pretty funny when tradeph is very quick to note a high volume of accidents within a few weeks of a roundabout's opening and details how unsafe they are, but very quick to dispute someone's report of a reduction in accidents, noting that more time is needed to see the big picture.

Btw, you are still cherry-picking data.

If I’m cherry picking data, then there must be plenty of 2x2 modern roundabouts that have low crash rates.  Cite these 2x2 roundabouts with low crash rates or your accusation rings hollow.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on November 09, 2015, 05:20:15 PM
This would be an eye opening study if it were published:

“The Safety Performance of Roundabouts with Average Daily Traffic exceeding 30,000”


The 30,000 ADT condition would weed out single-lane roundabouts and most 2x1 multi-lane roundabouts.  The focus would be nearly entirely on the safety performance of 2x2 (or higher) roundabouts in America. Ideally, the study would analyze interchange and non-interchange roundabouts separately and come up with two different sets of safety numbers.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on November 10, 2015, 05:03:04 PM
According to a 2014 article, the OPP have responded to 52 collisions at the Herb Gray Parkway multi-lane roundabout in Windsor, Ontario.  All the accidents were referred to as “minor accidents”.  Does this mean only minor injury accidents occurred or no injury accidents occurred at all?  The article doesn’t clarify. 
http://blackburnnews.com/chatham/chatham-news/2014/12/22/two-lane-roundabout-yields-accidents/

In addition, in April 2015 there were two separate tractor trailer rollovers inside the roundabout about a week apart. 
http://www.cbc.ca/news/canada/windsor/all-lanes-open-after-another-roundabout-rollover-at-highway-3-1.3043578


Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on November 14, 2015, 11:03:46 AM
The overall crash rate benefits may be "null and void," but these high volume intersections that require a multilane solution are the ones that lead to the vast majority of fatality crashes when they're signalized or have multi-way stop conditions. Without getting into the weeds of cost-benefit analysis,* a few more (or even many more) fender benders and whiplash accidents are massively preferable to a few more deaths from people being T-boned by red-light runners and the like.

* If we take the value of a human life at somewhere between $8-10 million (https://www.transportation.gov/sites/dot.gov/files/docs/VSL_Guidance_2014.pdf), even several hundred more accidents at $5-10k a pop would be "worth" it.

In a recent study, MDOT evaluated the performance and safety effectiveness of roundabouts in Michigan.  According to the cost-benefit crash analysis included in the study, triple-lane roundabouts saw a negative average benefit of -$122,778 annually.  The double-lane roundabout at 68th Ave & Randall St was the only 2x2 roundabout analyzed in the study; it too had a negative benefit.   

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/MDOTrb_zpsfygteugy.png)
https://www.michigan.gov/documents/mdot/MDOT_Research_Report_RC1566_379286_7.pdf

The safety improvements of roundabouts are mitigated as you get into high capacity double-lane (specifically 2x2) and triple-lane roundabouts.  The triple-lane roundabouts analyzed in the Michigan study saw a 19.9% reduction in injury crashes while total crashes increased by 97.5%.  The reduction in injury crashes wasn’t enough to offset the large increases in total crashes in the cost-benefit analysis.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on November 16, 2015, 10:16:58 AM
Here's a link to a presentation given by the FHWA at the 4th Annual International Conference on Roundabouts.  It is titled "The Mutli-Lane Roundabout  PDO Dilemma" and summarizes a lot of the points made on this thread. 

http://teachamerica.com/RAB14/RAB1410AIsebrands/index.htm

A few comments...
In the first slide, the speaker states that "they [multi-lane roundabouts] are showing great improvement in terms of the injury and fatal crashes".  However, she doesn't cite any evidence to support this and it's up to the listener to take her claim at face value. 

The Bluffton, SC roundabout is highlighted in this presentation and favorable crash statistics are shown.  However, the presenter questions whether crashes will go back up as drivers get use to the new markings.  In 2014, the roundabout experienced 30 total crashes including 7 injury crashes.  This equates to 2.5 crashes per month (much higher than the 0.4/month cited in the presentation).  Unfortunately, crashes have gone back up.

http://www.islandpacket.com/news/local/traffic/article33716778.html
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on December 21, 2015, 09:19:39 AM
This roundabout is going to be a doozy (scheduled for 2017):
(http://www.gannett-cdn.com/-mm-/5535823b363befef22d5776f449f2b0cc382d3de/c=21-0-513-655&r=537&c=0-0-534-712/local/-/media/Appleton/2014/07/24/-roundabout.jpg20140723.jpg)
http://www.postcrescent.com/story/news/local/2014/07/24/roundabout-coming-richmond-northland/13119107/

Is there any evidence that triple-lane roundabouts have reduced injury crashes in Wisconsin?
Title: Re: Crash prone 'modern roundabouts'
Post by: Rothman on December 22, 2015, 11:54:32 AM
Alright...triple-laners make me twitch.  I'll agree with your concern here, tradey.
Title: Re: Crash prone 'modern roundabouts'
Post by: AlexandriaVA on December 22, 2015, 12:18:10 PM
Egads. That's no roundabout. That's a corn-fed abomination!
Title: Re: Crash prone 'modern roundabouts'
Post by: cl94 on December 22, 2015, 02:36:10 PM
Alright...triple-laners make me twitch.  I'll agree with your concern here, tradey.

Um...yeah. There are very few places where a triple-lane roundabout makes sense. Basically only where it replaces a triple-lane traffic circle.
Title: Re: Crash prone 'modern roundabouts'
Post by: Zeffy on December 22, 2015, 06:23:21 PM
Two lanes should be the maximum for any circular intersection. Three lanes is just too much.
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on December 22, 2015, 06:29:50 PM
Alright...triple-laners make me twitch.  I'll agree with your concern here, tradey.

Um...yeah. There are very few places where a triple-lane roundabout makes sense. Basically only where it replaces a triple-lane traffic circle.
Two lanes should be the maximum for any circular intersection. Three lanes is just too much.

I can see triple-lane roundabouts at heavily-used junctions, but only as an upgrade from a two-lane roundabout. (I think the roundabout above (on the last page) will work function well as a traffic control device first, as a safety net second, but I think the roundabout would be better off as two lanes until traffic demands the third).
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on January 22, 2016, 05:55:41 PM
Route 62 and Morse Road roundabout in Gahanna, Ohio had the second most crashes in the mid-Ohio region from 2009 to 2011 (98 total crashes).   It also had the 5th highest number of injury crashes.  To combat this poor safety record, a circulating lane was removed and crashes have since gone down (a common theme in this thread).  They can always restripe it to a 2x2 roundabout if traffic conditions warrant it, but it should have been striped as a 2x1 roundabout to begin with.

http://www.morpc.org/trans/Safety_Top_intersections.pdf
Title: Re: Crash prone 'modern roundabouts'
Post by: Jovet on January 23, 2016, 02:00:17 AM
I said it before, I do not like multi-lane roundabouts. They are just too complicated, and can confuse drivers. 
I agree.  I think they're just inviting trouble!

Same for multi-lane four-way stops. Those drive me UP THE WALL!
Title: Re: Crash prone 'modern roundabouts'
Post by: Quillz on January 23, 2016, 11:53:09 PM
So, during my research, I came across this proposed roundabout design for the UK:

(http://i.imgur.com/mCg3nlw.png)

I mentioned this design in another thread. The idea is that it allows a motorist to get to their desired direction (left, straight, or right) without having to change any lanes, as each quarter-turn automatically shuffles off the proper lane. For usage in America, the turning would be reversed.
Title: Re: Crash prone 'modern roundabouts'
Post by: cl94 on January 24, 2016, 12:10:55 AM
So, during my research, I came across this proposed roundabout design for the UK:

(http://i.imgur.com/mCg3nlw.png)

I mentioned this design in another thread. The idea is that it allows a motorist to get to their desired direction (left, straight, or right) without having to change any lanes, as each quarter-turn automatically shuffles off the proper lane. For usage in America, the turning would be reversed.

That's roughly the design specified in the MUTCD. The Dutch call it a "turbo roundabout".
Title: Re: Crash prone 'modern roundabouts'
Post by: Quillz on January 24, 2016, 12:12:49 AM
So, during my research, I came across this proposed roundabout design for the UK:

(http://i.imgur.com/mCg3nlw.png)

I mentioned this design in another thread. The idea is that it allows a motorist to get to their desired direction (left, straight, or right) without having to change any lanes, as each quarter-turn automatically shuffles off the proper lane. For usage in America, the turning would be reversed.

That's roughly the design specified in the MUTCD. The Dutch call it a "turbo roundabout".
Interesting to see it's in the MUTCD. I've never driven on one, but it seems to make a great deal of sense, especially since one of the biggest issues with roundabouts is people attempting to lane change. This design would seemingly solve that problem. Of course, most of the roundabouts I've been on are single-lane to begin with, making this design unnecessary.
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on January 24, 2016, 12:36:50 AM
So, during my research, I came across this proposed roundabout design for the UK:

http://i.imgur.com/mCg3nlw.png

I mentioned this design in another thread. The idea is that it allows a motorist to get to their desired direction (left, straight, or right) without having to change any lanes, as each quarter-turn automatically shuffles off the proper lane. For usage in America, the turning would be reversed.

That's roughly the design specified in the MUTCD. The Dutch call it a "turbo roundabout".

Interesting to see it's in the MUTCD. I've never driven on one, but it seems to make a great deal of sense, especially since one of the biggest issues with roundabouts is people attempting to lane change. This design would seemingly solve that problem. Of course, most of the roundabouts I've been on are single-lane to begin with, making this design unnecessary.

Are you sure you've never driven on a turbo roundabout (or at least the American interpretation)? If you come to one, there's a very good chance it has spiral markings.

In my area, the first multi-lane roundabouts were striped with spiral markings. They were built in the early 2000s.
Title: Re: Crash prone 'modern roundabouts'
Post by: Quillz on January 24, 2016, 12:39:45 AM
I don't believe I've been on one. Every roundabout I've driven one had effectively an off-ramp, if you will, that didn't force you to take it if you didn't want to. But it was single-lane, so it couldn't do that.
Title: Re: Crash prone 'modern roundabouts'
Post by: roadfro on January 24, 2016, 01:20:06 AM
So, during my research, I came across this proposed roundabout design for the UK:

(http://i.imgur.com/mCg3nlw.png)

I mentioned this design in another thread. The idea is that it allows a motorist to get to their desired direction (left, straight, or right) without having to change any lanes, as each quarter-turn automatically shuffles off the proper lane. For usage in America, the turning would be reversed.

That's roughly the design specified in the MUTCD. The Dutch call it a "turbo roundabout".

Note that the MUTCD does not "specify" any roundabout designs, or govern any roadway designs in general. The MUTCD only regulates the signs, striping, etc. used in roadway design.

A "turbo roundabout" is two of several roundabout pavement marking examples depicted in the MUTCD. (Figure 3C-5 is a two-lane roundabout with one-lane exits; Figure 3C-12 is a three-lane roundabout with two-lane exits. Other examples show partial turbos for unique situations.)
Title: Re: Crash prone 'modern roundabouts'
Post by: english si on January 24, 2016, 05:09:38 AM
So, during my research, I came across this proposed roundabout design for the UK:

(http://i.imgur.com/mCg3nlw.png)
Spiral roundabouts like that are, in the UK, only used when the conflict points are fully signalised.

This is the most blatent one https://www.google.co.uk/maps/@53.5498467,-2.260033,347m/data=!3m1!1e3 with certain routes colour-coded on the pavement.
Title: Re: Crash prone 'modern roundabouts'
Post by: Kacie Jane on January 24, 2016, 01:21:38 PM
So, during my research, I came across this proposed roundabout design for the UK:

http://i.imgur.com/mCg3nlw.png

I mentioned this design in another thread. The idea is that it allows a motorist to get to their desired direction (left, straight, or right) without having to change any lanes, as each quarter-turn automatically shuffles off the proper lane. For usage in America, the turning would be reversed.

That's roughly the design specified in the MUTCD. The Dutch call it a "turbo roundabout".

Interesting to see it's in the MUTCD. I've never driven on one, but it seems to make a great deal of sense, especially since one of the biggest issues with roundabouts is people attempting to lane change. This design would seemingly solve that problem. Of course, most of the roundabouts I've been on are single-lane to begin with, making this design unnecessary.

Are you sure you've never driven on a turbo roundabout (or at least the American interpretation)? If you come to one, there's a very good chance it has spiral markings.

In my area, the first multi-lane roundabouts were striped with spiral markings. They were built in the early 2000s.

Note that in the drawing, there are three lanes entering at each approach, one for each direction.  Every roundabout I've come across around Puget Sound has at least straight and right-turning traffic approach in the same lane.

Now that I've written that second sentence, I'm not 100% confident in its accuracy.  There may in fact be some where right turning traffic is alone and straight through traffic is paired with left turning traffic instead.  But that's not the important part.
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on January 24, 2016, 03:16:28 PM
So, during my research, I came across this proposed roundabout design for the UK:

http://i.imgur.com/mCg3nlw.png

I mentioned this design in another thread. The idea is that it allows a motorist to get to their desired direction (left, straight, or right) without having to change any lanes, as each quarter-turn automatically shuffles off the proper lane. For usage in America, the turning would be reversed.

That's roughly the design specified in the MUTCD. The Dutch call it a "turbo roundabout".

Interesting to see it's in the MUTCD. I've never driven on one, but it seems to make a great deal of sense, especially since one of the biggest issues with roundabouts is people attempting to lane change. This design would seemingly solve that problem. Of course, most of the roundabouts I've been on are single-lane to begin with, making this design unnecessary.

Are you sure you've never driven on a turbo roundabout (or at least the American interpretation)? If you come to one, there's a very good chance it has spiral markings.

In my area, the first multi-lane roundabouts were striped with spiral markings. They were built in the early 2000s.

Note that in the drawing, there are three lanes entering at each approach, one for each direction.  Every roundabout I've come across around Puget Sound has at least straight and right-turning traffic approach in the same lane.

Sorry, I wasn't being specific enough. My point was that it boggled my mind that Quillz has never seen a multi-lane roundabout with spiral markings, since our first roundabouts have had spiral markings for 10 or 11 years now (although, the markings have changed over the years to become slightly less ambiguous).
Title: Re: Crash prone 'modern roundabouts'
Post by: Quillz on January 25, 2016, 12:05:24 PM
I don't know what is so mind boggling. The only roundabouts I've ever personally driven on have been single laned.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on January 25, 2016, 12:29:19 PM
Here’s a recent article by mlive spinning the safety performance of the State and Ellsworth roundabout.  The writer of the article just can’t admit that this roundabout has been a failure from a safety perspective:

Quote
There are some instances of total crash rates increasing after the addition of a roundabout. A good example of this is the State Street and Ellsworth Road intersection, but even in those cases, the numbers of serious injury and fatal crashes have dropped sharply. At the State and Ellsworth intersection, there were 97 crashes between 2008 and 2012 and 12 of them—12 percent—were injury crashes. In 2014 alone there were 171 crashes, but just 6—3.5 percent—involved injuries.
http://www.mlive.com/news/ann-arbor/index.ssf/2016/01/roundabouts_spreading_as_count.html

Before the roundabout the signalized intersection averaged 2.4 injury crashes per year (12 injury crashes / 5 years of data).  After the roundabout, it has averaged 6 injury crashes per year (6 injury crashes / 1 year of data).   Based on the facts presented in the article, the roundabout has seen a significant increase in injury crashes, not a decrease.   
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on January 25, 2016, 12:41:39 PM
I don't know what is so mind boggling. The only roundabouts I've ever personally driven on have been single laned.

Then try driving a 2 or 3 lane roundabout.
Title: Re: Crash prone 'modern roundabouts'
Post by: PurdueBill on January 25, 2016, 01:23:05 PM
Here’s a recent article by mlive spinning the safety performance of the State and Ellsworth roundabout.  The writer of the article just can’t admit that this roundabout has been a failure from a safety perspective:

Quote
There are some instances of total crash rates increasing after the addition of a roundabout. A good example of this is the State Street and Ellsworth Road intersection, but even in those cases, the numbers of serious injury and fatal crashes have dropped sharply. At the State and Ellsworth intersection, there were 97 crashes between 2008 and 2012 and 12 of them—12 percent—were injury crashes. In 2014 alone there were 171 crashes, but just 6—3.5 percent—involved injuries.
http://www.mlive.com/news/ann-arbor/index.ssf/2016/01/roundabouts_spreading_as_count.html

Before the roundabout the signalized intersection averaged 2.4 injury crashes per year (12 injury crashes / 5 years of data).  After the roundabout, it has averaged 6 injury crashes per year (6 injury crashes / 1 year of data).   Based on the facts presented in the article, the roundabout has seen a significant increase in injury crashes, not a decrease.   

So this particular intersection went from having a crash every 2-3 weeks in 2008-12 to having one every other day and they are calling that progress?  How can the writer of that article write what they did with a straight face?  Sure the percent of injury crashes is lower...the number of total accidents per year is up 780 percent!!  The crash numbers seem to indicate that something is very wrong with that roundabout, not very right as they paint it.
Title: Re: Crash prone 'modern roundabouts'
Post by: Rothman on January 25, 2016, 02:33:34 PM
I see lane confusion happening in the posted roundabout design.  Take the top quarter where lane 3 of the roundabout goes left and then you're left with lanes 4 and 1 that split into three lanes.  Which lane do I go in?  Looks like a recipe for disaster.
Title: Re: Crash prone 'modern roundabouts'
Post by: Quillz on January 25, 2016, 02:38:31 PM
I don't know what is so mind boggling. The only roundabouts I've ever personally driven on have been single laned.

Then try driving a 2 or 3 lane roundabout.
If there were any around here, I probably would. Most of the roundabouts in California right now are either built by Caltrans at state highways junctions with high traffic incidents, or locally built and maintained by neighborhoods. Neither of those are close to me, the closest on for me would be the CA-154/CA-246 junction near Solvang, which consists of a single lane that lets you stay on CA-154, turn west onto CA-246, or east onto a local road.
Title: Re: Crash prone 'modern roundabouts'
Post by: roadfro on January 27, 2016, 10:17:00 AM
I see lane confusion happening in the posted roundabout design.  Take the top quarter where lane 3 of the roundabout goes left and then you're left with lanes 4 and 1 that split into three lanes.  Which lane do I go in?  Looks like a recipe for disaster.

You stay in your same lane, the one directly ahead of you. You're not supposed to change lanes in a roundabout.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on March 04, 2016, 02:36:40 PM
The Homer Watson roundabout saw over 100 crashes in 2014.  Add it to the 100+ roundabout crash club.  The crash problem at this roundabout has gotten worse each year since its construction in 2011.

Quote
Homer Watson roundabout remains a trouble spot
...the roundabout was installed in 2011. That year there were 51 collisions. The number grew to 53 in 2012, 72 in 2013 and 107 in 2014.  Bob Henderson, manager of transportation engineering, presented the 2014 collision report for regional roads at a meeting Tuesday.  He said the problem at the roundabout is human behaviour, according to a review completed earlier this year. Traffic volume has also increased.  "The design's good at the intersection," he said.

http://m.kitchenerpost.ca/news-story/6122856-regional-road-collision-report-homer-watson-roundabout-remains-a-trouble-spot

Title: Re: Crash prone 'modern roundabouts'
Post by: Brian556 on March 04, 2016, 11:26:58 PM
Quote
Same for multi-lane four-way stops. Those drive me UP THE WALL!

Never thought of it like this but good point.

Multi-lane all way stops create issues if they are on a heavily traveled roadway cause if you are in the right lane, and another vehicle is in the left lane, that vehicle blocks your view and you can't see if anybody is in the oncoming left turn lane that you need to wait for.

Dixon Ln in Flower Mound Texas is like that. Three all-way stops in a row on a four lane divided street. One intersection needs signals, the others need two way stops. Vehicles often back up to 8 deep at the first all way stop because the previous intersection is signalized. In this case the first all way stop is at a busy high school driveway, and the other two are at residential street intersections that do not need them.

This situation is utterly ridiculous. It's weird cause the town of Flower Mound is very good at sign and signal maintenance, but shitty at engineering and application of traffic control.

Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on March 07, 2016, 11:22:08 AM
The woman being interviewed in that video works at the Tim Hortons next to the roundabout.  According to her, everyday there is “some type of fender bender, some type of accident”.  You can look at the numbers and say there were only 107 crashes in 2014… she must be exaggerating.  But really, a lot of the crashes that occur at a roundabout don’t get reported because many of them are minor fender benders.  It's the roundabout crashes that result in significant vehicle damage where the cops are more likely to get called out. 

It would be interesting to compare the reported vs. non-reported crashes at roundabouts vs. signalized intersections.  At the State & Ellsworth roundabout in Ann Arbor there were over 170 crashes in a year.  But how many accidents involving broken tail-lights and cracked bumpers didn’t get reported?   I wouldn't be at all surprised if that Ann Arbor roundabout averages a crash a day (be it reported or unreported). 
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on March 07, 2016, 12:09:42 PM
The woman being interviewed in that video works at the Tim Hortons next to the roundabout.  According to her, everyday there is “some type of fender bender, some type of accident”.  You can look at the numbers and say there were only 107 crashes in 2014… she must be exaggerating.  But really, a lot of the crashes that occur at a roundabout don’t get reported because many of them are minor fender benders.  It's the roundabout crashes that result in significant vehicle damage where the cops are more likely to get called out. 

It would be interesting to compare the reported vs. non-reported crashes at roundabouts vs. signalized intersections.  At the State & Ellsworth roundabout in Ann Arbor there were over 170 crashes in a year.  But how many accidents involving broken tail-lights and cracked bumpers didn’t get reported?   I wouldn't be at all surprised if that Ann Arbor roundabout averages a crash a day (be it reported or unreported). 


No doubt the same type bumps occur at regular intersections as well.  Accidents usually leave broken parts behind, so I'm sure there would be a lot of plastic lying around the roundabout if there were accidents everyday.

If there's significant damage, they're supposed to be reported to the police anyway, even after the fact.  I would think most insurance companies would want such a police report.  Thus, I'm sure some of the 107 accidents at the intersection include some where the police didn't actually respond to it.

Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on March 07, 2016, 01:29:32 PM
Is the percentage of unreported crashes higher at roundabouts or higher at signalized intersections?  That’s the question I’m interested in.  The only way to figure that out is to actually record them and cross reference the crashes that were observed in the video to the police reports that were filed.  It’s not scientific enough to say “well, I don’t see any plastic pieces laying around the roundabout today… I guess there’s not a crash problem”. 

A lot of people won’t report a fender bender because they don’t want their insurance to go up.  Sure, a $120,000 dollar Maserati gets rear-ended and the cops will probably be called.   But for every Maserati there are thousands of Chevy Malibu’s on the road.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on March 08, 2016, 12:11:59 PM
It’s not just total crashes that are a problem at the Homer Watson roundabout.  According to the record, injuries have more than doubled since the roundabout opened in 2011.  This is another example of a large multi-lane roundabout seeing a spike in total crashes with no reduction in injury crashes (a lose-lose).   The argument has been that crashes that occur at a roundabout are low impact “fender benders”.  If that is true, how did 40 people get injured at the Homer Watson roundabout in just the first 3 years of operation?   

Quote
Its safety performance is not as poor as the dangerous roundabout it overtook, Homer Watson Boulevard at Block Line Road. After opening in 2011, the Kitchener intersection saw its collisions soar to 282 from 44, while injuries more than doubled to 40 people hurt from 16 hurt. This compares its first three-plus years as a roundabout to its last three-plus years as a traffic light. The second-busiest roundabout shed seven per cent of its traffic in 2014 to fall to second place.

http://m.therecord.com/news-story/6218115-86-crashes-in-first-17-months-collisions-soar-at-new-cambridge-roundabout
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on March 08, 2016, 07:30:09 PM

I think they're a bit too close to each other.  I also went during rush hour.

I'd rather have two closely spaced roundabouts than two closely spaced signals. Then again, they don't seem that close?

These work just fine. A bit slow at rush hour but compared to the old signals it's a big improvement.

(http://images.tapatalk-cdn.com/15/05/20/434e6b90f4e62f7968f4416834fa3ba0.jpg)

These two roundabouts in Hilliard were the #1 & #3 most crash prone intersections in the entire state of Ohio for the years 2013-2015.  There were 218 crashes at the Cemetery/Main roundabout and 119 crashes at the Main/Scioto Darby roundabout.  Hell, even the Google streetview car captured a crash at the roundabout:

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/untitledtest2_zpsincgcpjj.png)

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Ohiotop10_zps3csyc94q.png)

http://branlawfirm.com/most-dangerous-intersections-in-ohio/
Title: Re: Crash prone 'modern roundabouts'
Post by: johndoe on March 08, 2016, 07:53:48 PM
https://www.google.com/maps/@43.4183801,-80.470737,110m/data=!3m1!1e3 (https://www.google.com/maps/@43.4183801,-80.470737,110m/data=!3m1!1e3)

The Homer Watson roundabout appears to have an ICD of about 200', so it's not undersized.  Do you see any patterns in the crash reports?  You can see they striped out the third circulating lane for the SB approach, I wonder if crashes were reduced after they made that change.
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on March 08, 2016, 08:36:01 PM
It’s not just total crashes that are a problem at the Homer Watson roundabout.  According to the record, injuries have more than doubled since the roundabout opened in 2011.  This is another example of a large multi-lane roundabout seeing a spike in total crashes with no reduction in injury crashes (a lose-lose).   The argument has been that crashes that occur at a roundabout are low impact “fender benders”.  If that is true, how did 40 people get injured at the Homer Watson roundabout in just the first 3 years of operation?

What constitutes an injury? Technically, both breaking your neck and straining your neck are injuries. A t-bone collision could result in several broken bones, but no deaths, and would be labelled an "injury collision". Equally, being rear-ended and bumping your head on the steering wheel is also an "injury collision" (presuming one sought medical attention, reporting the injury to insurance).

As we've previously discussed, there are multiple levels of injuries. Injuries may have increased, but it's the severity that matters. It's ridiculous to support an intersection design that (perhaps) puts people in hospital for months, but oppose an intersection design that results in several visits to a chiropractor, simply because there's fewer injuries overall.

If one were to put a price tag on "emotional distress" caused by collisions (as many lawyers do, in order to offset the loss of income from being in hospital), my guess is that 6 or 7 really bad injury crashes is still much pricier than 40 or 50 head-bumps and neck-strains.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on March 09, 2016, 08:40:54 AM
The Homer Watson roundabout appears to have an ICD of about 200', so it's not undersized.  Do you see any patterns in the crash reports?  You can see they striped out the third circulating lane for the SB approach, I wonder if crashes were reduced after they made that change.

To be honest I’m not sure when the third lane was striped out at the Homer Watson roundabout.  Here’s a youtube video posted April 2013 where the SB approach was still 3-lanes. 

In my opinion this is a properly sized roundabout.  It is large enough where there is separation between legs of traffic yet small enough where drivers aren’t circulating around at high speeds.  Yet there were 40 injuries in the first 3 years of operations.  One thing you notice in the video is that a pedestrian crossing the roundabout can lead to ‘gridlock’.  Perhaps the large number of crashes and injuries can be attributed to the high pedestrian volumes at this roundabout.  This is just a guess though since I haven’t gone through the crash reports.  Before this roundabout was built, residents voiced concerns that a busy roundabout shouldn’t be constructed next to a high school with heavy pedestrian traffic.    In October 20011, shortly after the roundabout opened, a 16-year old St. Mary’s High School student was struck by a bus while she was walking in the crosswalk.   She experienced significant injuries.  In the news reports you could see the indentation her head made with the buses windshield.   This accident placed a negative light on the roundabout in the community and the city has been trying to make the roundabout safer ever since (ie. reducing a circulating lane at one of the legs, placing stopping guards during school times, etc).
   
As we've previously discussed, there are multiple levels of injuries. Injuries may have increased, but it's the severity that matters. It's ridiculous to support an intersection design that (perhaps) puts people in hospital for months, but oppose an intersection design that results in several visits to a chiropractor, simply because there's fewer injuries overall.

Roundabouts can be the site of serious, life altering accidents.  Just ask Cassi Lam who was the 16-year old girl struck at the Homer Watson roundabout.  The article I cited touches on another roundabout in the Waterloo region.  The roundabout at Hespeler Road and Queen Street “…went from 15 total collisions that hurt nine people to 86 total collisions that hurt six people. This compares its last 17 months as a traffic light to its first 17 months as a roundabout. The average severity of injury did not change and the roundabout had one more injury-causing collision than the traffic signal, although fewer people were hurt.” 
Title: Re: Crash prone 'modern roundabouts'
Post by: PurdueBill on March 09, 2016, 08:38:38 PM
Things like the above are what has me wondering about the wisdom of the push for a roundabout at State Street and River Road (former IN 26 and US 231) in West Lafayette.  The push is to make State Street so much more pedestrian and bike friendly, increasing foot traffic from Chauncey Hill down to the Levee, but through a roundabout? With tipsy students heading to and from bars at night? Between multilane streets that carry significant commuter traffic to and from campus from and to Lafayette? Seems like asking for trouble.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on March 10, 2016, 12:54:57 PM
It sounds like they are axing their plans to build a roundabout at State Street and River Road.   The roundabout footprint would encroach onto private property making it cost prohibitive.  Even if it wasn’t cost prohibitive they shouldn’t build it because it’s just not the right location for a roundabout (for the reasons mentioned by PurdueBill).

http://www.purdueexponent.org/city/article_e57dcfac-825e-5df8-9ae8-08b2c8a4f343.html#comments

Title: Re: Crash prone 'modern roundabouts'
Post by: PurdueBill on March 10, 2016, 01:15:16 PM
It sounds like they are axing their plans to build a roundabout at State Street and River Road.   The roundabout footprint would encroach onto private property making it cost prohibitive.  Even if it wasn’t cost prohibitive they shouldn’t build it because it’s just not the right location for a roundabout (for the reasons mentioned by PurdueBill).

http://www.purdueexponent.org/city/article_e57dcfac-825e-5df8-9ae8-08b2c8a4f343.html#comments



That hopefully will stick.  Can you imagine asking McDonald's to close again after the old one was shut down and demolished for the River Road work that rerouted US 231?  There is too much pedestrian and bicycle traffic for the roundabout to work there.  It seems that West Lafayette has been going kinda wild with stuff on roads that INDOT left to them; the signals at Northwestern and Stadium were in fine working order and not that old but needed to be replaced because they weren't pretty enough--same for Northwestern and Grant.  The roundabouts at Northwestern and Yeager and at new and old SR 25 have their issues without adding pedestrians and bicycles to the mix in large quantity.
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on March 10, 2016, 04:03:15 PM
Why not signalize the pedestrian crossings at roundabouts? Some sort of pole-mounted HAWK setup might work well.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on March 11, 2016, 01:42:39 PM

The non-compliance rate at the HAWK is high especially for drivers exiting the roundabout.   A driver exiting the roundabout may not see that the HAWK signal is activated in time or they may be worried about being rear ended if they come to a stop so close to the roundabout exit.  And a lot of the drivers that do come to a stop are stopping for too long.  They treat the alternating flashing red signals like a railroad crossing (wait until the lights stop flashing).  This just leads to more gridlock and drivers backing up through the roundabout.  I find it curious that the HAWK video only demonstrates pedestrians crossing the entry leg of the roundabout.  Why not show what it looks like crossing the exit leg?  That’s when you see drivers backing up through the roundabout and causing gridlock.

Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on March 11, 2016, 02:44:21 PM
The non-compliance rate at the HAWK is high especially for drivers exiting the roundabout.

How high is the compliance rate for a normal crosswalk? We're discussing the lesser of two evils here.

A driver exiting the roundabout may not see that the HAWK signal is activated in time or they may be worried about being rear ended if they come to a stop so close to the roundabout exit.  And a lot of the drivers that do come to a stop are stopping for too long.  They treat the alternating flashing red signals like a railroad crossing (wait until the lights stop flashing).  This just leads to more gridlock and drivers backing up through the roundabout.  I find it curious that the HAWK video only demonstrates pedestrians crossing the entry leg of the roundabout.  Why not show what it looks like crossing the exit leg?  That’s when you see drivers backing up through the roundabout and causing gridlock.

All of those things could be said about a normal crosswalk at a roundabout (backing up through the circle, not stopping because of a fear of being rear-ended, etc). I'm simply saying that, legally, crosswalks have to be provided somewhere at every intersection (or at least I'm pretty sure they are) The HAWK may have compliance issues now, but in several years, as drivers come to understand their meaning, I suspect that they'll provide a superior crossing option for roundabouts, especially those with two or more lanes. They force drivers to stop for 8-10 seconds to let pedestrians cross, and then go to a flash mode so drivers can continue, should there not be any more pedestrians.

Pedestrian safety at roundabouts seem to be related to drivers stopping right at the crosswalk, making the pedestrian invisible to subsequent lanes. The pedestrian assumes right-of-way because one car stopped, but the car in the next lane cannot see the pedestrian, and the two collide. HAWK signals force traffic to stop farther back, so visibility isn't hindered as much.

There's also an operational advantage. Rather than having traffic stop every 10-15 seconds to let one person cross, traffic stops every 60-80 seconds to let three or four people cross. Perhaps the parallel leg could also be timed so that the pedestrians can cross both the ingress and egress leg of the roundabout at the same time.
Title: Re: Crash prone 'modern roundabouts'
Post by: Tarkus on March 12, 2016, 04:16:03 AM
Both the conventional and HAWK situations with pedestrians in roundabouts are problematic, because of that exit point issue, which could potentially lock up the entire circular roadway in the right (wrong) traffic load and travel patterns.  If you're going to get into a situation where the traffic is going to have to stop within the circular roadway, you might as well have the crosswalk go across the circular roadway instead of across the approach.

Or better yet, don't build a roundabout in a spot with high pedestrian volumes, especially a multi-lane one where motorists seem to have enough difficulty processing the information to enter the circular roadway safely, without having to worry about another mode of transportation coming from yet another angle.  With the phased approach of signalized intersections, you don't have pedestrians going one direction locking up an entire intersection.

Theoretically, if you were going through all the trouble of installing a HAWK at a multi-lane roundabout like Homer Watson/Block Line, for the cost, I almost wonder if it may make as much as sense to meter the roundabout approaches like freeway onramps.  After all, the circular roadway in a roundabout is just a really miniature beltway.  It'll eliminate the decision-making of determining when it's safe to enter the multi-lane fray (the decision becomes objective rather than subjective), the red phases could be prolonged as needed when there's pedestrians without the nasty lockup issue, and the conflict points would become less . . .conflicting. 
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on March 12, 2016, 10:16:49 AM
The HAWK may have compliance issues now, but in several years, as drivers come to understand their meaning, I suspect that they'll provide a superior crossing option for roundabouts, especially those with two or more lanes.

A 2011 study analyzed the performance of a Pedestrian Hybrid Beacon (PHB, also known as HAWK) at a three-lane roundabout in Oakland County, Michigan.  A link to the 115 page report is below.  The chart on page 49 lists the driver behavior at the HAWK during different signal intervals along the three-lane approach.  During the steady red / walk phase, 94.4% of drivers came to a stop at the entry leg.  However, only 68.9% of drivers came to a stop at the exit leg.  Nearly 1 in 3 drivers exiting the roundabout disregarded the solid red and drove through the crosswalk when a WALK indication was being displayed to the pedestrian.  Drivers appear to be less aware of the HAWK signal on the exit leg.  It’s not necessarily that drivers don’t know what to do; they just aren’t reacting in time. 

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Compliance_zpsmkhnlbef.png)
http://www.rcocweb.org/Lists/Publications/Attachments/126/HAWK%20Final%20Report%202011.pdf

Ok, but would the HAWK be safer than a roundabout with no signalized crosswalks?  I would argue NO.  Pedestrians get a false sense of security when a “WALK” indication is displayed.  Personally, my head is on a swivel when crossing the road, but I see so many pedestrians barely paying attention, just assuming it’s safe to step into the crosswalk because their “WALK” came up.  That pedestrian behavior can be dangerous when 31.1% of drivers are disregarding the solid red indication.
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on March 12, 2016, 02:52:24 PM
Ok, but would the HAWK be safer than a roundabout with no signalized crosswalks?  I would argue NO.  Pedestrians get a false sense of security when a “WALK” indication is displayed.  Personally, my head is on a swivel when crossing the road, but I see so many pedestrians barely paying attention, just assuming it’s safe to step into the crosswalk because their “WALK” came up.  That pedestrian behavior can be dangerous when 31.1% of drivers are disregarding the solid red indication.

That's for sure. I saw the RRFB in that study you linked above. That looks like a promising alternative, though the HAWK looks promising for entry legs, and I suspect exit-leg compliance may increase over time as HAWKs become more commonplace; my suspicion is that driver's have about the same reaction time to the HAWK as they do to the pedestrians themselves. So, I don't think there's any harm in installing HAWK signals. After all, the alternative is signalized junction with the same WALK/DON'T WALK signals, and about the same number of people who are either swiveling their heads around, or not looking at all.

We really ought to consider Pelican phasing, like in the UK. They use the standard R/Y/G signal setup, with solid red during the WALK phase, and flashing amber during the DON'T WALK phase. If the iffy compliance with HAWK signals has anything to do with failure to understand the signals themselves, perhaps compliance would go up when people meet a standard traffic light.


Though I will agree that roundabouts are not a particularly good idea in urban areas (though one-lane roundabouts likely work fine in both urban and rural areas alike), we still have to consider the safety of pedestrians even in the most remote of roundabouts. Unless we plan on dumping them altogether (a bad idea), we need to find a way to make the pedestrian crossings at roundabouts safer.

In terms of the ADA, they may prefer signalized crossings at roundabouts. Those who are blind have trouble telling when it's safe to cross. The Pelican crossing above has a chirping noise for the WALK phase, and may be helpful for those individuals.
Title: Re: Crash prone 'modern roundabouts'
Post by: english si on March 12, 2016, 07:17:31 PM
^^ there's also a spinning cone under the box with the button as an added feature for sensory impaired people.
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on March 13, 2016, 03:12:44 AM
^^ there's also a spinning cone under the box with the button as an added feature for sensory impaired people.

Tom Scott demonstrated that feature in one of his videos. Genius idea..

Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on March 21, 2016, 02:34:43 PM
Another driver was killed at a roundabout in Carmel.   Of the roughly 100 roundabouts in Carmel, three have been the site of a fatal crash since 2014.  Here are news reports of the fatal crashes that have occurred:

Fatal crashes at Carmel roundabouts:
http://fox59.com/2014/08/06/one-dead-in-carmel-accident-passenger-taken-to-hospital/
http://fox59.com/2014/09/26/person-dead-after-motorcycle-accident-in-carmel/
http://www.indystar.com/story/news/crime/2016/03/18/driver-killed-carmel-roundabout-crash/81967984/
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on March 21, 2016, 03:52:13 PM
Another driver was killed at a roundabout in Carmel....http://www.indystar.com/story/news/crime/2016/03/18/driver-killed-carmel-roundabout-crash/81967984/

If distraction is at play here, he could have just as easily run a stop sign or signal. At least he hit the central concrete decorations instead of another car.
Title: Re: Crash prone 'modern roundabouts'
Post by: paulthemapguy on March 21, 2016, 04:31:30 PM
I was at that pair of Hilliard roundabouts just last month!  People in Ohio have no idea how to use them, apparently.  It was chaos!  I thought a yield sign at each and every approach would make them pretty self-explanatory...nope!  And if this is kind of like a big 6-way intersection, why not install one big roundabout to accommodate all 3 through-roads.

(sidenote:  there's a really sweet comic/games shop called Packrat Comics right near these roundabouts.  That's why I ended up in that area XD)
Title: Re: Crash prone 'modern roundabouts'
Post by: Tarkus on March 22, 2016, 05:33:08 AM
Another driver was killed at a roundabout in Carmel.   Of the roughly 100 roundabouts in Carmel, three have been the site of a fatal crash since 2014.  Here are news reports of the fatal crashes that have occurred:

Fatal crashes at Carmel roundabouts:
http://fox59.com/2014/08/06/one-dead-in-carmel-accident-passenger-taken-to-hospital/
http://fox59.com/2014/09/26/person-dead-after-motorcycle-accident-in-carmel/
http://www.indystar.com/story/news/crime/2016/03/18/driver-killed-carmel-roundabout-crash/81967984/

The interesting thing to note about that latest Carmel crash is that it occurred at the Westfield Blvd and E 96th St roundabout (https://www.google.com/maps/@39.9271462,-86.1267491,213m/data=!3m1!1e3), which is a three-leg single-lane roundabout with one right turn bypass from Westfield NB to 96th EB.  Based on a quickie measurement on Google Maps, the center island is about 120 ft. in diameter.  The crash did occur on St. Patrick's Day at night, so one can't rule out impairment, but there's no indication of that yet in the news reports.

If distraction is at play here, he could have just as easily run a stop sign or signal. At least he hit the central concrete decorations instead of another car.

Considering that he got all the way to the middle of the roundabout, I'd say the type of intersection is moot.  If the impact with the central island was severe enough to kill him, reason stands that had there been another car in the roundabout there, it could have been just as ugly as a wreck at a stop or signal-controlled intersection.  There's not much deflection at the Westfield/96th roundabout--this also appears to be the case with the 106th/Pennsylvania and 126th/Hazel Dell roundabouts, which were the sites of the previous accidents.

It's also worth noting that in every case, we're looking at single-vehicle fatal fixed object collisions caused by hitting curbing, and resulting in particularly violent impacts.  I'd be curious to see the stats for these three roundabouts in question.

Edit: Doing a little research (typed in 96th and Westfield accident Carmel), and found there was another fatal accident at this same roundabout in 2007, which killed two (http://www.theindychannel.com/news/2-men-killed-in-carmel-crash).  The car was found in the center island.  Another news story (http://www.wthr.com/story/7201916/police-driver-was-drunk-in-carmel-roundabout-crash) has police saying that the driver was drunk and entered the roundabout going "at least 62mph".
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on March 22, 2016, 10:57:29 AM
There are roughly 100 modern roundabouts in Carmel, Indiana with 4 known fatal roundabout crashes occurring since their inception.  So how does that compare to other parts of the country?  I decided to look at the fatalities that have occurred at the 100 most crash prone intersections in SE Michigan.  I chose SE Michigan because it has publically accessible data for every intersection in the region dating back a decade.  Of the 100 most crash prone intersections in SE Michigan, there have been 29 fatal crashes (23% of the intersections were the site of a fatal crash and 4% had multiple fatal crashes).

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/top100Rbs_zpsxv15qfla.png)
http://semcog.org/data-and-maps/high-frequency-crash-locations

The numbers initially look pretty good for the roundabouts.  There were only 4 fatal crashes at the 100 Carmel roundabouts compared to 29 fatal crashes at the 100 most crash prone intersections in SE Michigan.  This equates to an 86% reduction in fatal crashes.  However, there are some important factors to consider:

#1.  There are roughly 100 roundabouts in Carmel, but back in 2005 - the first year crash data was analyzed for the intersections in SE Michigan - there were only about a half dozen roundabouts in Carmel.  The roundabout craze hadn’t taken off yet.   This doesn’t make it a fair comparison and underestimates the fatal crashes that may have occurred in Carmel had there been 100 roundabouts back in 2005. 

#2.   Carmel has a population of roughly 85,000 people whereas SE Michigan has a population of 4.7 million people.  Analyzing the top 100 crash prone intersections in a region of 4.7 million people is going to be weighted towards high volume intersections whereas many of the Carmel roundabouts are single-lane with relatively low traffic volumes.  Obviously, intersections with 70,000 vehicles per day (ie. major SE Michigan intersections) are more likely to see a fatal crash than an intersection with 15,000 vehicles per day (ie. single-lane Carmel roundabouts). 

#3.  I don’t have an accurate database of the Carmel crashes and am relying on news articles to estimate how many fatal roundabout crashes have actually occurred over the past 10 years.  Potentially, the fatal crashes that have occurred inside Carmel roundabouts are being underestimated.

Based on these 3 factors, the 86% reduction in fatal crashes isn’t as good as it sounds.  There is one more caveat though.  This is looking at fatal crashes and not total fatalities.  When looking at total fatalities, the numbers might look better for the Carmel roundabouts (since a fatal crash at an intersection may be more prone to multiple fatalities).  I just didn’t take the time to parse through the crash forms to see how many fatalities occurred in each of the 29 fatal crashes.  This can be easily done though.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on March 22, 2016, 12:14:10 PM
Let’s look at it this way… Over the past 27 months, the 100 roundabouts in Carmel has been the site of 3 fatal crashes.  That equates to an average of 1.33 fatal crashes per year.  The top 100 crash prone SE Michigan intersections have seen on average 2.9 fatal crashes per year. 

(1.33/2.9) -1 = -54%   

Factor #1 is dealt with in this shorter 27 month analysis since we are comparing crash data from roughly 100 roundabouts to 100 SE Michigan intersections.  But we are getting farther and farther away from the 90% reduction in fatal crashes.  The Carmel roundabouts are now only seeing a 54% reduction in fatal crashes.  And we still haven’t dealt with Factor #2.  The traffic volumes at Carmel roundabouts aren’t as high as the intersections in SE Michigan.  Many of the SE Michigan intersections have traffic volumes double and triple that of the single-lane roundabouts found in Carmel.  If you factor in the traffic volumes, the reduction in fatalities at Carmel roundabouts just hasn't been that impressive.

It’s been alluded to that the majority of people dying at roundabouts are drunk.  The safety numbers stated in the literature is that roundabouts reduce fatalities by 90%.  That is the number I’m focusing on and it includes alcohol related fatal crashes.  You can’t just ignore a fatality because somebody was drunk.
Title: Re: Crash prone 'modern roundabouts'
Post by: lordsutch on March 22, 2016, 10:08:58 PM
Heck, if *only* half as many people are dying instead of a tenth as many people, let's just tear all the roundabouts out and let the carnage recommence.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on March 23, 2016, 07:30:58 AM
Heck, if *only* half as many people are dying instead of a tenth as many people, let's just tear all the roundabouts out and let the carnage recommence.

Having 50% less fatalities in Carmel isn't that impressive when the typical Carmel roundabout has 50% less traffic though.  Over the past 27 months, the fatality rate at Carmel roundabouts has been similar to the fatality rate at non-roundabout communities.  Carmel has had a bad run over the past 27 months when it comes to fatalities at roundabouts. 
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on March 23, 2016, 01:16:08 PM
Heck, if *only* half as many people are dying instead of a tenth as many people, let's just tear all the roundabouts out and let the carnage recommence.

Having 50% less fatalities in Carmel isn't that impressive when the typical Carmel roundabout has 50% less traffic though.  Over the past 27 months, the fatality rate at Carmel roundabouts has been similar to the fatality rate at non-roundabout communities.  Carmel has had a bad run over the past 27 months when it comes to fatalities at roundabouts.

Have you compared Carmel's crash stats to other cities of the same population?
Title: Re: Crash prone 'modern roundabouts'
Post by: Tarkus on March 23, 2016, 03:25:19 PM
Having 50% less fatalities in Carmel isn't that impressive when the typical Carmel roundabout has 50% less traffic though.

Exactly.  It's about the per MEV rate.

I'm still looking around to see if the crash data is easily accessible for Carmel.  As much as I love to bag on ODOT, at least they have a publicly-searchable crash statistics database.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on March 23, 2016, 03:26:47 PM
Have you compared Carmel's crash stats to other cities of the same population?

Dearborn, Michigan has a population of 98,153 compared to Carmel’s population of 85,927.  Over the past 3 years there have been 3 fatal crashes at Dearborn’s top 100 most crash prone intersections.  There have also been 3 fatal crashes at Carmel’s roughly 100 roundabouts during the same time period.  Maybe Carmel has been on the wrong side of the bell curve lately, but for whatever reason there has been a string of roundabout fatalities in the city of Carmel.

Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on March 23, 2016, 03:40:05 PM
Have you compared Carmel's crash stats to other cities of the same population?

Dearborn, Michigan has a population of 98,153 compared to Carmel’s population of 85,927.  Over the past 3 years there have been 3 fatal crashes at Dearborn’s top 100 most crash prone intersections.  There have also been 3 fatal crashes at Carmel’s roughly 100 roundabouts during the same time period.  Maybe Carmel has been on the wrong side of the bell curve lately, but for whatever reason there has been a string of roundabout fatalities in the city of Carmel.

Why not expand the year measure to 10 years? 20 years? That's solid data. You seem hard-set on the last three years, which are clearly Carmel's worst.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on March 23, 2016, 04:44:11 PM
Why not expand the year measure to 10 years? 20 years? That's solid data. You seem hard-set on the last three years, which are clearly Carmel's worst.

Roundabouts didn’t exist in Carmel 20 years ago.  Even 10 years ago there were maybe only a half-dozen to a dozen roundabouts in the city.  It’s hard to analyze data that doesn’t exist.
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on March 23, 2016, 04:58:49 PM
He's well known to cherry pick data. And because an accident occured near a roundabout and had nothing to do with the functionality of a roundabout (such as a drunk driving straight into the center) doesn't change his opinion that the roundabout itself is defective.
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on March 23, 2016, 05:14:13 PM
Why not expand the year measure to 10 years? 20 years? That's solid data. You seem hard-set on the last three years, which are clearly Carmel's worst.

Roundabouts didn’t exist in Carmel 20 years ago.  Even 10 years ago there were maybe only a half-dozen to a dozen roundabouts in the city.  It’s hard to analyze data that doesn’t exist.

You'd be analyzing before/after data.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on March 23, 2016, 05:53:12 PM
Carmel, the self-proclaimed roundabout capital of America, had the same number of fatal crashes as Dearborn, Michigan (a city with ZERO roundabouts).  That's a fact everybody can excuse away all they want.  Have fun with that. 
Title: Re: Crash prone 'modern roundabouts'
Post by: lordsutch on March 23, 2016, 10:59:09 PM
Carmel, the self-proclaimed roundabout capital of America, had the same number of fatal crashes as Dearborn, Michigan (a city with ZERO roundabouts).  That's a fact everybody can excuse away all they want.  Have fun with that. 

What you call "excus[ing] away," statisticians call "controlling for other variables." But sure, we'll play your game. Compare the number of fatal accidents in Dearborn to fatal accidents in Carmel, not over your cherry-picked last 27 months, but the last 10 years - a nice, even, round number, nothing up my sleeve.

Until you do at least that, as far as I'm concerned you're not engaging in honest research, you're just engaging in a vendetta against a type of intersection you seem to personally and irrationally dislike.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on March 24, 2016, 12:10:34 AM
^Carmel currently has 95 roundabouts.  I'm comparing the fatal crashes of 100 Dearborn intersections to the fatal crashes of 95 Carmel roundabouts.  Each year you go back there are fewer and fewer Carmel roundabouts to analyze.  It wouldn't be fair to compare the number of fatal crashes at Dearborn's 100 most dangerous intersections over the past decade to the number of fatal crashes at Carmel's roundabouts (since 10 years ago, there were only about a dozen roundabouts in Carmel).  That's apples to bananas.  Admittedly this is a back of the napkin analysis, but your suggestion totally throws off the numbers.  While we are at it, you might as well compare the fatal crashes in Chicago to Billings, Montana. 

I just believe the safety benefits of roundabouts are being over estimated.  Keep in mind, the national safety numbers so often cited in literature is based on a study that is over 15 years old.  Roundabouts have evolved at lot since 2000 when the Insurance Institute for Highway Safety released their report.  The more recent safety studies on roundabouts have found that in many cases total crashes are going up (ie. Wisconsin study found a 12% increase in total crashes, not a 39% decrease as cited in the 2000 IIHS study).  You mention "honest research", yet there are so many DOTs that cite the 2000 IIHS study like it is gospel to push for a roundabout.  That to me isn't honest either.
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on March 24, 2016, 01:11:56 AM
^Carmel currently has 95 roundabouts.  I'm comparing the fatal crashes of 100 Dearborn intersections to the fatal crashes of 95 Carmel roundabouts.  Each year you go back there are fewer and fewer Carmel roundabouts to analyze.  It wouldn't be fair to compare the number of fatal crashes at Dearborn's 100 most dangerous intersections over the past decade to the number of fatal crashes at Carmel's roundabouts (since 10 years ago, there were only about a dozen roundabouts in Carmel).  That's apples to bananas.  Admittedly this is a back of the napkin analysis, but your suggestion totally throws off the numbers.  While we are at it, you might as well compare the fatal crashes in Chicago to Billings, Montana.

Deerborn has 100 conventional signals. 10 years ago, Carmel had mostly signals, so 10 years ago, the cities had much more in common. Now that Carmel has more roundabouts, the comparison would be whether or not fatal collisions in Carmel have dropped over time with the new roundabouts, and whether or not the not number of fatal collisions in Deerborn has dropped or stayed constant since they didn't change anything.

The comparison is Carmel, who changed over to roundabouts, to Deerborn, who changed nothing.
Title: Re: Crash prone 'modern roundabouts'
Post by: Landshark on March 26, 2016, 02:52:07 PM
Carmel, the self-proclaimed roundabout capital of America, had the same number of fatal crashes as Dearborn, Michigan (a city with ZERO roundabouts).  That's a fact everybody can excuse away all they want.  Have fun with that.

Carmel & Dearborn are apples to oranges.   One is older dense innercity, the other sprawly modern suburbia.   Not only do the physical designs greatly differ, but so do the demographics.  I am sure Carmel has lower % of transit ridership, longer average auto trips, etc.   I also wouldn't be surprised if the average speed limit was also higher in Carmel vs. Dearborn. 



Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on March 27, 2016, 01:08:40 PM
Carmel & Dearborn are apples to oranges.   One is older dense innercity, the other sprawly modern suburbia.   Not only do the physical designs greatly differ, but so do the demographics.  I am sure Carmel has lower % of transit ridership, longer average auto trips, etc.   I also wouldn't be surprised if the average speed limit was also higher in Carmel vs. Dearborn. 

Take Troy, Michigan as the comparison.  Troy has roughly the same population as Carmel and is the poster child for “suburban sprawl”.  Over the past 4 years the 100 most crash prone intersections in Troy has been the site of 3 fatal crashes.  This is the same number of fatal crashes as Carmel’s roundabouts over the same time period.  All things being equal, Carmel should have had fewer fatal crashes:

#1.  This analysis is comparing the fatal crashes of 100 Troy intersections to only 95 Carmel roundabouts.  And back in 2013, there was only about 60-70 roundabouts in Carmel.  Even though fewer intersections were analyzed, Carmel had the same number of fatal crashes as Troy. 

#2.  Average traffic volumes at Troy intersections are likely much higher than the Carmel roundabouts.  Some of the intersections in Troy experience 70,000 vehicles per day.  I don’t know of a single roundabout in the entire country with traffic counts approaching that.  Even though the Carmel roundabouts have lower traffic volumes, they had the same number of fatal crashes.   

The fact is over the past 4 years Carmel roundabouts have been the site of 3 fatal crashes.  Other similarly sized communities in the United States have had the same number of fatalities as Carmel has had.  Where is the 90% reduction in fatal crashes?
Title: Re: Crash prone 'modern roundabouts'
Post by: roadfro on March 27, 2016, 07:16:02 PM
We really ought to consider Pelican phasing, like in the UK. They use the standard R/Y/G signal setup, with solid red during the WALK phase, and flashing amber during the DON'T WALK phase. If the iffy compliance with HAWK signals has anything to do with failure to understand the signals themselves, perhaps compliance would go up when people meet a standard traffic light.


Just catching up on this thread after several weeks. I know it's a bit off topic, but I had to chime in to agree with this statement.

I have not been a fan of the HAWK signal style since I saw it proposed for the 2009 MUTCD. The Pelican crossing signal demonstrated here makes much more sense intuitively, in the context of existing signal indications, and addresses two things I don't like with a HAWK (signal is dark until ped activation, and the wig-wag red). The only downside is that you couldn't use the Pelican signal at the entrance to a roundabout, as was mentioned earlier in the thread—although really, a signal at the entrance to a roundabout is counter-intuitive to the roundabout controls anyway...
Title: Re: Crash prone 'modern roundabouts'
Post by: renegade on April 05, 2016, 08:21:53 AM
I think I'll leave this here ...

http://www.mlive.com/news/ann-arbor/index.ssf/2016/04/road_commission_improves_state.html#incart_river_home

Number of crashes at State and Ellsworth roundabout drops following initial spike

It's getting better.  The idiots are beginning to learn how to navigate it.  And it's not nearly as bad as someone who does not live here makes it out to be.  I have to deal with it every day, and have yet to see an accident.  I don't think anyone has died there, either.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on April 05, 2016, 08:34:57 PM
I think I'll leave this here ...

http://www.mlive.com/news/ann-arbor/index.ssf/2016/04/road_commission_improves_state.html#incart_river_home

Number of crashes at State and Ellsworth roundabout drops following initial spike

It's getting better.  The idiots are beginning to learn how to navigate it.  And it's not nearly as bad as someone who does not live here makes it out to be.  I have to deal with it every day, and have yet to see an accident.  I don't think anyone has died there, either.

Here is ten years of crash data for State and Ellsworth (green = pre-roundabout; yellow=roundabout construction year; red = post-roundabout).  You can spin it however you like, but the fact is there has been a spike in total crashes without a reduction in injury crashes.  I didn't see 2015 injury accidents listed in the article renegade cited so that was not included in the chart.

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/untitled11ystats_zpse5i7jcwm.png)
http://semcog.org/Data-and-Maps/High-Frequency-Crash-Locations/Point_Id/81016689/view/RoadIntersectionCrashDetail
Title: Re: Crash prone 'modern roundabouts'
Post by: kphoger on April 07, 2016, 02:01:08 PM
#2.  Average traffic volumes at Troy intersections are likely much higher than the Carmel roundabouts.  Some of the intersections in Troy experience 70,000 vehicles per day.  I don’t know of a single roundabout in the entire country with traffic counts approaching that.  Even though the Carmel roundabouts have lower traffic volumes, they had the same number of fatal crashes. 

Then what we need is a comparison between signalized intersections and roundabouts where traffic volumes are comparable as well as city sizes.  This would yield apples-to-apples data to review:  similar city sizes make for a meaningful comparison of total crashes and fatalities, while similar traffic volumes made for a meaningful comparison of intersection designs.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on April 08, 2016, 10:14:37 AM
I just find it ironic that Carmel Indiana, the roundabout capital of America, has had the same number of fatal crashes as similarly sized communities with zero roundabouts.  Articles will keep regurgitating the IIHS safety stat that says modern roundabouts reduce fatal crashes by 90%.  If you say it enough times it must be true.  A lot of people on this thread believe it.
Title: Re: Crash prone 'modern roundabouts'
Post by: paulthemapguy on April 08, 2016, 12:29:10 PM
I can't see roundabouts reducing the number of fatal crashes if they occur in low-speed areas...But then again you shouldn't be putting roundabouts on highways with high speeds in the first place!  If someone proposed a roundabout on a high speed roadway, I'd say, "you're gonna put a big circle in the middle of a road where the speed is 45-55mph?  Are you serious?"  Doesn't stop some agencies though.
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on April 08, 2016, 12:40:15 PM
I can't see roundabouts reducing the number of fatal crashes if they occur in low-speed areas...But then again you shouldn't be putting roundabouts on highways with high speeds in the first place!  If someone proposed a roundabout on a high speed roadway, I'd say, "you're gonna put a big circle in the middle of a road where the speed is 45-55mph?  Are you serious?"  Doesn't stop some agencies though.

See NJ 70/72. https://goo.gl/maps/c6XhdHMXcVn  Although it's a Jersey traffic circle, it does have roundabout features (everyone yields prior to entering).  Speed limits on 3 of the spokes are 55 mph; on the other 2 spokes, limits are 50 mph.

No issues here.  You wouldn't think it by looking at the aerial photos, but it can jam up during rush hours!
Title: Re: Crash prone 'modern roundabouts'
Post by: JMAN_WiS&S on April 08, 2016, 12:47:00 PM
The multi lane roundabout at US 53 and Town Hall Rd south of the US 53/I94 interchange in Eau Claire Wisconsin has been subject to quite a few crashes recently and now the DOT is proposing changes such as building the mound up in the center, and replacing the current advanced warning signs with fluorescent ones, even though the ones on US 53 have flashers on them. The major issue is the speed limit right in the area is 55 mph and the roundabout limit is 15.
Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on April 08, 2016, 12:48:57 PM
I can't see roundabouts reducing the number of fatal crashes if they occur in low-speed areas...But then again you shouldn't be putting roundabouts on highways with high speeds in the first place!  If someone proposed a roundabout on a high speed roadway, I'd say, "you're gonna put a big circle in the middle of a road where the speed is 45-55mph?  Are you serious?"  Doesn't stop some agencies though.

See NJ 70/72. https://goo.gl/maps/c6XhdHMXcVn  Although it's a Jersey traffic circle, it does have roundabout features (everyone yields prior to entering).  Speed limits on 3 of the spokes are 55 mph; on the other 2 spokes, limits are 50 mph.

No issues here.  You wouldn't think it by looking at the aerial photos, but it can jam up during rush hours!


Just a single one? Not a big deal!  How about a real chain?
https://www.google.com/maps/place/Albany,+NY/@42.6428116,-73.8497982,16z/data=!3m1!1e3!4m2!3m1!1s0x89de0a34cc4ffb4b:0xe1a16312a0e728c4
55 MPH posted throughout.

I often compare roundabout construction with prescribing insulin: in the right situation is a life saver, but insulin doesn't help broken bones or pneumonia...
Title: Re: Crash prone 'modern roundabouts'
Post by: kphoger on April 08, 2016, 01:04:27 PM
Just a single one? Not a big deal!  How about a real chain?
https://www.google.com/maps/place/Albany,+NY/@42.6428116,-73.8497982,16z/data=!3m1!1e3!4m2!3m1!1s0x89de0a34cc4ffb4b:0xe1a16312a0e728c4
55 MPH posted throughout.

That doesn't even make sense to be signed at 55 mph.  Looks like 45 might be more appropriate.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on April 08, 2016, 01:25:27 PM
^On streetview it appears Slingerlands Bypass is posted at 45 mph through the roundabouts.  It only increases to 55 mph once you get past the string of roundabouts.   Kalvado, is it possible the speed limit was just recently reduced?  The streetview images are from September 2015. 
Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on April 08, 2016, 01:34:36 PM
^On streetview it appears Slingerlands Bypass is posted at 45 mph through the roundabouts.  It only increases to 55 mph once you get past the string of roundabouts.   Kalvado, is it possible the speed limit was just recently reduced?  The streetview images are from September 2015.
I wish I remember. I drive there once every few months. I am usually on a slower side of things going 60. But I never been there during rush hour.
Before roundabouts that used to be posted 55.
Title: Re: Crash prone 'modern roundabouts'
Post by: Sykotyk on April 08, 2016, 10:26:47 PM
Just one clarification for those discussing the Carmel/SE Michigan statistics.... In Carmel you're counting ONLY the 100 roundabouts, while in SE Michigan you're counting the top 100 most crash prone intersections, rather than ALL intersections.

Let's say there's 10,000 intersections covered under the data used for SE Michigan.

Now the data is 4/100 to 29/10,000.

These are supposed to be safer. In a lot of instances, they are not. And the main culprit, to me, is that many people do not know what the YIELD sign truly means. They're used to STOP, and in the absence of STOP their thought is to go. We see it on on-ramps all the time where the YIELD sign on the ramp is never heeded. They weave into traffic, cut off cars in the right lane, flip you off for not letting them over, etc. They don't consider it an actionable sign.

This has been ingrained for decades for some of these people and now suddenly throwing a 'new' type of interchange at them will not get them to stop their bad habits. It just amplifies them.
Title: Re: Crash prone 'modern roundabouts'
Post by: kphoger on April 08, 2016, 10:45:08 PM
I've never seen the problem at roundabouts to be a failure to yield. No, I've seen much more confusion arise when a driver can't STOP yielding. At some point, you have to grow some balls and GO already.
Title: Re: Crash prone 'modern roundabouts'
Post by: Sykotyk on April 09, 2016, 12:56:13 AM
I've never seen the problem at roundabouts to be a failure to yield. No, I've seen much more confusion arise when a driver can't STOP yielding. At some point, you have to grow some balls and GO already.

But that has nothing to do with an accident. A car doesn't get hit in the roundabout because a driver is timid to enter.

An accident occurs because a car enters when they're not supposed to.

The problem is, a roundabout should be treated in the same manner as a four-way stop. If it's just one car from one approach, you get to go unimpeded. If it's two cars, then the same process as a stop sign (vehicle to the right goes, if it's on-coming traffic, they can both go). if it's W and S that arrive, S gets to go first because they're on the right.

That's generally understood by the populus (though, there are many I've seen that don't understand when you get to go at a jammed four-way stop sign). The issue is when a roundabout is jammed with traffic stalled at 2, 3, or 4 approaches. The first car into the roundabout gives the impression to those behind them that they can 'tag along' and suddenly that entire approach clears the roundabout while the other approaches all have to wait. And that's when you get cars slightly behind the line racing to get up into the roundabout before another approach can start. And then the next approach begins to clear out in the same manner.

It should be one-at-a-time in a counter-clockwise fashion, just as a stop sign. This isn't the big traffic circles found in New England. These are much smaller and REPLACE stop-signed or signalized intersections. The circle is not a road in the manner of how a large traffic circle, generally found in the New England states, is basically entering an entirely new road, one that is one-way and forms a loop.

That's the problem I've come across. And it's especially true during rush hour when a roundabout is placed on a major thoroughfare at an intersection with a less used crossroad. The thoroughfare treats it like they get constant stream of traffic and the side roads have to wait. Rather than the car behind the car at a yield sign realizing they must wait until the first car at each other approach also clears the roundabout. And THEN they get to go. Same as a stop sign.

Instead, it's treated as "since the car in front of me is the only one in the roundabout, I can enter because I don't have to yield to anyone on my left". Which is true, but it makes entering the roundabout an aggressive act, rather than a defensive/regulated act.
Title: Re: Crash prone 'modern roundabouts'
Post by: english si on April 09, 2016, 07:19:57 AM
That doesn't even make sense to be signed at 55 mph.  Looks like 45 might be more appropriate.
Surely US drivers are capable of not driving at the speed limit if it is unsafe to do so there. Oh wait...

These are on a 70mph Dual Carriageway trunk road (https://www.google.co.uk/maps/@52.0124053,-1.1233869,13.58z). (BTW, the UK doesn't allow reduced limit for one thing like a junction, preferring ample warning signs, rumble strips, and drivers to not be slaves to driving to the posted limit. Nor does it allow traffic signals on 70mph roads). AADT on the A43 is around 37000 in this area (between 36200 north of Brackley and 37800 south of the A421). Looking, it seems that each roundabout on the A43 (with the exception of the ones at the M40, where there was a terrible 'improvement' scheme that has now been reversed) seems to get about 8 collisions every 5 years, with perhaps 1 of them fatal. There's room for improvement, but the only way to do it is grade-separation (which, as well as expensive and gaining little in journey time savings, will increase the number of idiots driving 100mph along the road, undermining all the safety benefits as more people crash off, killing themselves).
Title: Re: Crash prone 'modern roundabouts'
Post by: english si on April 09, 2016, 07:39:13 AM
But that has nothing to do with an accident. A car doesn't get hit in the roundabout because a driver is timid to enter.
Do accident stats only include those on the circulatory carriageway, or also at approaches? A timid driver is likely to get driven into the back of. And they also create accidents around them - you even give an example of how: a not very assertive driver creates a queue, and when they go, the queue thinks its clear for them.

Better driver education would go a long way to improving US roundabout safety.
Title: Re: Crash prone 'modern roundabouts'
Post by: kphoger on April 09, 2016, 10:23:05 AM
But that has nothing to do with an accident. A car doesn't get hit in the roundabout because a driver is timid to enter.
Do accident stats only include those on the circulatory carriageway, or also at approaches? A timid driver is likely to get driven into the back of. And they also create accidents around them - you even give an example of how: a not very assertive driver creates a queue, and when they go, the queue thinks its clear for them.

Better driver education would go a long way to improving US roundabout safety.

Also...  A driver too timid to go from the entering left lane makes for an obstruction the right-lane driver might not be able to see around; said right-lane driver might take an unwarranted chance at entering the roundabout out of impatience.

Also...  What I've seen more often is drivers who become timid within the circulating roadway, sometimes coming to a full stop inside the roundabout.  This most certainly does increase the risk of accident.
Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on April 09, 2016, 01:36:27 PM
Also...  What I've seen more often is drivers who become timid within the circulating roadway, sometimes coming to a full stop inside the roundabout.  This most certainly does increase the risk of accident.

We have a roundabout with a crosswalk 10' from the outer circle. I've been there in both capacities - and as pedestrian, I am really scared since you are not seen until last second. You better wait until traffic gap.. and then someone hits their brakes and stops in the middle of the circle...  Hopefully they will not hit me when rear-ended...
As a driver, I am really scared of pedestrians in that crosswalk - whatever I do would be wrong, both stopping in the circle and  not yielding to crosswalker..
Title: Re: Crash prone 'modern roundabouts'
Post by: english si on April 09, 2016, 01:56:19 PM
We have a roundabout with a crosswalk 10' from the outer circle.
That's too close. Needs to be more like 30' - especially on the exit side of the roundabout.

When we have crossings next to roundabouts (normally one, maybe two, car lengths from it) in the UK, they aren't ones that give priority to pedestrians (though obviously road vehicles don't have the right to hit them), but we will have signalised crossings or zebras (where cars are meant to yield to pedestrians waiting to cross) if they are a bit further down the road and the visibility and stacking issues are sorted.
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on April 09, 2016, 04:06:58 PM
Also...  What I've seen more often is drivers who become timid within the circulating roadway, sometimes coming to a full stop inside the roundabout.  This most certainly does increase the risk of accident.

We have a roundabout with a crosswalk 10' from the outer circle. I've been there in both capacities - and as pedestrian, I am really scared since you are not seen until last second. You better wait until traffic gap.. and then someone hits their brakes and stops in the middle of the circle...  Hopefully they will not hit me when rear-ended...
As a driver, I am really scared of pedestrians in that crosswalk - whatever I do would be wrong, both stopping in the circle and  not yielding to crosswalker..

Have a link for that roundabout?
Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on April 09, 2016, 07:57:41 PM

We have a roundabout with a crosswalk 10' from the outer circle. I've been there in both capacities - and as pedestrian, I am really scared since you are not seen until last second. You better wait until traffic gap.. and then someone hits their brakes and stops in the middle of the circle...  Hopefully they will not hit me when rear-ended...
As a driver, I am really scared of pedestrians in that crosswalk - whatever I do would be wrong, both stopping in the circle and  not yielding to crosswalker..

Have a link for that roundabout?
https://www.google.com/maps/@42.689025,-73.8315784,71m/data=!3m1!1e3
southwestern leg crossing mostly - it is used by students walking between dorms and campus.
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on April 09, 2016, 08:44:08 PM
That's a standard design but it's way too close. College near me has one like that as well.  Moving it about 100 feet from the roundabout allows for a little storage room.
Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on April 09, 2016, 10:02:21 PM
That's a standard design but it's way too close. College near me has one like that as well.  Moving it about 100 feet from the roundabout allows for a little storage room.
If you look carefully, there is a foot path which cut across roundabout approach curve, saving maybe 10 feet. You really think that same people would walk 100 feet just because that is where crosswalk is marked?  Then you may be interested in buying that bridge on the interstate!
It is just the case when roundabout was built  for the sake of building a roundabout.  There were a lot of other improvements within that project, but they could be implemented without a circle - and probably at a lower cost.
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on April 09, 2016, 10:26:43 PM
What's preventing less from just crossing into the center right now?

There are methods to keep people using the crosswalks. Decorative fencing, for example.

(ugh...less should have been "peds"!!!
Title: Re: Crash prone 'modern roundabouts'
Post by: Sykotyk on April 10, 2016, 02:05:36 AM
What's preventing less from just crossing into the center right now?

There are methods to keep people using the crosswalks. Decorative fencing, for example.

Considering people have to extol energy to walk, making them walk further just makes the find a shortcut. Have you ever seen a grassy area near a building with a well worn foot path because people were too lazy to walk the extra 10-15-20 feet to stay on pavement? Same issue. Only way to stop them would be to line the entire thing with fencing, and that would last as long as the first tractor trailer that goes up and over the curb or drunk at night sideswipes it. And since it's decorative only, it won't stand up to the abuse. And unless its repaired/replaced quickly, it will look like a guady eyesore.

Title: Re: Crash prone 'modern roundabouts'
Post by: johndoe on April 10, 2016, 09:41:31 AM
The problem is, a roundabout should be treated in the same manner as a four-way stop.

if it's W and S that arrive, S gets to go first because they're on the right.

It should be one-at-a-time in a counter-clockwise fashion, just as a stop sign.

The thoroughfare treats it like they get constant stream of traffic and the side roads have to wait.

they must wait until the first car at each other approach also clears the roundabout. And THEN they get to go. Same as a stop sign.

"I can enter because I don't have to yield to anyone on my left". Which is true

Forgive me if this is harsh, but I don't think you understand roundabouts.  Everything I've quoted is wrong.  A roundabout is not a four-way stop.  Entering drivers yield to conflicting vehicles in the circulating roadway; it has nothing to do with the other approaches. 
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on April 10, 2016, 09:51:49 AM
The problem is, a roundabout should be treated in the same manner as a four-way stop.

if it's W and S that arrive, S gets to go first because they're on the right.

It should be one-at-a-time in a counter-clockwise fashion, just as a stop sign.

The thoroughfare treats it like they get constant stream of traffic and the side roads have to wait.

they must wait until the first car at each other approach also clears the roundabout. And THEN they get to go. Same as a stop sign.

"I can enter because I don't have to yield to anyone on my left". Which is true

Forgive me if this is harsh, but I don't think you understand roundabouts.  Everything I've quoted is wrong.  A roundabout is not a four-way stop.  Entering drivers yield to conflicting vehicles in the circulating roadway; it has nothing to do with the other approaches. 

His one-car-at-a-time idea would hopelessly jam up the roundabout approaches. It take a car a second or two to go thru an intersection. It would take a car several seconds to go thru a roundabout, especially if making a left or u-turn.
Title: Re: Crash prone 'modern roundabouts'
Post by: Sykotyk on April 10, 2016, 12:19:14 PM
The problem is, a roundabout should be treated in the same manner as a four-way stop.

if it's W and S that arrive, S gets to go first because they're on the right.

It should be one-at-a-time in a counter-clockwise fashion, just as a stop sign.

The thoroughfare treats it like they get constant stream of traffic and the side roads have to wait.

they must wait until the first car at each other approach also clears the roundabout. And THEN they get to go. Same as a stop sign.

"I can enter because I don't have to yield to anyone on my left". Which is true

Forgive me if this is harsh, but I don't think you understand roundabouts.  Everything I've quoted is wrong.  A roundabout is not a four-way stop.  Entering drivers yield to conflicting vehicles in the circulating roadway; it has nothing to do with the other approaches. 

How can anything you quoted be 'incorrect' when I specifically stated "should" in the very first line. It was my opinion.

The problem with roundabouts is people race to be the next one in, rather than following a set pattern on how to enter the roundabout. Wouldn't a four-way stop be just as dangerous if there were no set manner to enter other than 'whoever gets into the intersection first?'
Title: Re: Crash prone 'modern roundabouts'
Post by: Sykotyk on April 10, 2016, 12:27:54 PM
The problem is, a roundabout should be treated in the same manner as a four-way stop.

if it's W and S that arrive, S gets to go first because they're on the right.

It should be one-at-a-time in a counter-clockwise fashion, just as a stop sign.

The thoroughfare treats it like they get constant stream of traffic and the side roads have to wait.

they must wait until the first car at each other approach also clears the roundabout. And THEN they get to go. Same as a stop sign.

"I can enter because I don't have to yield to anyone on my left". Which is true

Forgive me if this is harsh, but I don't think you understand roundabouts.  Everything I've quoted is wrong.  A roundabout is not a four-way stop.  Entering drivers yield to conflicting vehicles in the circulating roadway; it has nothing to do with the other approaches. 

His one-car-at-a-time idea would hopelessly jam up the roundabout approaches. It take a car a second or two to go thru an intersection. It would take a car several seconds to go thru a roundabout, especially if making a left or u-turn.

How would it jam up the approaches anymore than they already are? More than one can be in a roundabout at the same time. But, only one approach at a time in rotation should get to go.

In a roundabout, there is no pattern. It's 'every man, woman, and child for themselves' and what I see at roundabouts is vehicles driving dangerously fast and cutting into the roundabout so they can get through it without waiting.  As for 'yielding' even that is onerous simply because how much space to yield is left up to the one at the yield sign. Yield to traffic in the roundabout would mean the entire roundabout. Or, 10 feet. Whichever doesn't damage their bumper.

And that's not even getting into two-lane or more roundabouts, where now you have merging traffic and lane-changing traffic to deal with, where the worst of it is on your right, the blindside of your vehicle.

Then we're not even discussing the elephant in the room, and that's just inattentive and ignorant drivers who don't know or are unable to handle a particular situation. A stop sign or traffic light has order and structure. A roundabout doesn't. Primarily because they weren't really taught to those who started driving 10-15 or more years ago. Where a yield sign generated delineated financial responsibility for an accident, rather than a steadfast traffic rule. Highway onramps a testament to that.
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on April 10, 2016, 01:54:50 PM
How would it jam up the approaches anymore than they already are? More than one can be in a roundabout at the same time. But, only one approach at a time in rotation should get to go.

Quote
they must wait until the first car at each other approach also clears the roundabout. And THEN they get to go. Same as a stop sign.
Title: Re: Crash prone 'modern roundabouts'
Post by: kphoger on April 10, 2016, 03:00:00 PM
Wouldn't a four-way stop be just as dangerous if there were no set manner to enter other than 'whoever gets into the intersection first?'

But that IS the only set manner to enter a four-way-stop. The only time yielding to the right comes in to play at all is when two cars get there at exactly the same time, which is NOT most of the time. And there are some jurisdictions where yielding to the right isn't even codified, but rather a common courtesy.

In other words, there is a set pattern on how to enter a four-way stop intersection, and that pattern is this: Whoever gets there first goes first; if you and the car to your right get there at the same time, then yield to the other driver (that last part may or may not be codified). Similarly, there is a set pattern on how to enter a roundabout: if nobody is imminently approaching on your left, then go on through; if someone is imminently approaching on your left, then yield.

If all four vehicles approach a roundabout at exactly the same time, then nobody has to wait at all: each can safely enter the roundabout because no other car is yet imminently approaching on the left. If all four vehicles approach a four-way stop at exactly the same time, then nobody quite knows who should go first, and then everyone has to wait one by one.
Title: Re: Crash prone 'modern roundabouts'
Post by: Sykotyk on April 10, 2016, 09:19:58 PM
Wouldn't a four-way stop be just as dangerous if there were no set manner to enter other than 'whoever gets into the intersection first?'

But that IS the only set manner to enter a four-way-stop. The only time yielding to the right comes in to play at all is when two cars get there at exactly the same time, which is NOT most of the time. And there are some jurisdictions where yielding to the right isn't even codified, but rather a common courtesy.

In other words, there is a set pattern on how to enter a four-way stop intersection, and that pattern is this: Whoever gets there first goes first; if you and the car to your right get there at the same time, then yield to the other driver (that last part may or may not be codified). Similarly, there is a set pattern on how to enter a roundabout: if nobody is imminently approaching on your left, then go on through; if someone is imminently approaching on your left, then yield.

If all four vehicles approach a roundabout at exactly the same time, then nobody has to wait at all: each can safely enter the roundabout because no other car is yet imminently approaching on the left. If all four vehicles approach a four-way stop at exactly the same time, then nobody quite knows who should go first, and then everyone has to wait one by one.

When there's already traffic at the intersection, that last line is exactly how it's done. If there's already two cars ahead of you and a line at the other three approaches, you simply wait your turn. Not trying to remember whether you got to the intersection before someone else and go in that order. You go in the sequential order that's already been started. Counter-clockwise, around and around until eventually the traffic is clear.

At a round-about, there is no traffic pattern or rule other than 'yield to traffic in circle' which leaves a wide breadth as to how much space to yield. You get people gunning it to be the next one in the circle, regardless which 'turn' would've been there's at a stop sign. And then you get followers, who continue with the person in front of them. Which effectively becomes a four-phase traffic light with random phases.

And technically, if you're to yield to traffic in the circle, you have to yield to all traffic in the circle, not just whether you can floor it and get out in time before getting T-boned. Including oncoming traffic. Again, if a roundabout is that congested, it should be cleared out similar to a four-way stop: traffic on the right goes first, counter-clockwise, until all the approaches are clear.

Modern roundabouts that are replacing intersections (small medians, not the large 100-200ft behemoths that I consider traffic circles or rotaries like in the northeast), work best on roads that handle intermittent traffic from all directions when traffic volumes generally don't clog up an intersection.

US 59 & US 169 in Garnett, Kansas is a decent example. Two roads with intermittent traffic. It's not steady from any one approach. It's better than signalized, and a lot better than a stop-sign. It works because the intersection never saw a pressing need for other action (four-lane with a median and at-grade ramp system with stop-signs to break up traffic). Most of the time, you'll approach that traffic circle and be the first to go through without impeding traffic from another direction.

You put that roundabout in a downtown, urban, or suburban setting, and suddenly you get traffic. The roundabout doesn't relieve traffic, it only relieves wait times for a signal. But, enough traffic forces its wait time back to a signalized intersection. One thing roundabouts do, though, is create 'steady flow' for business and sidestreet traffic.

Imagine you're pulling out of a business that's just down the road from a traffic circle in a congested area. You constantly have traffic to deal with. Where, before, in a signalized intersection, you have a light that will temporarily block the flow of traffic before the turn phase begins for the perpendicular approaches.

https://goo.gl/maps/AVixtAFGkg32

Brattleboro, VT exit from I-89 to VT/NH-9 & US5. Don't make the mistake of stopping at the second gas station south (the one not at the roundabout). You will have a bear of a time pulling out as you have, essentially, free-flowing freeway traffic exiting to either US5 or NH-9. Or, the through traffic on US-5. If there were a light, you would have occassional pauses to pull out to make the left back to either the highway, north on US-5 or east on NH-9.

Roundabouts/traffic circles have their place. But, a lot of them are being shoehorned into congested areas where they don't serve the need well.

And a lot of that has to do with how drivers handle them. It's a free-for-all, rather than a traffic-control-device. We've seen it for decades with the YIELD sign at the end of on-ramps. Drivers do not heed them. Hell, there's many drivers you'll come across absolutely irate if you don't yield to the on-ramp traffic. That lack of respect and legality to a yield sign has carried over to the roundabout. That yield sign might as well not exist with how little people respect it.

What they need is to remove the YIELD sign and replace it with a STOP sign and a white regulatory sign underneath that states something along the lines of, "For Traffic In Circle Only" similar in manner to how "Except Right Turn" gets placed under many stop signs where the through line turns right at an intersection.

People, overwhelmingly, respect stop signs compared to yield signs. The lack of enforcement for "Failure To Yield" at a yield sign, anywhere, is astounding. At a stop sign, it's much more enforced. Which leads to compliance.

We can have a million and one 'Don't Text and Drive' or 'Don't Drink and Drive' but not one 'Yield means Yield' campaigns.
Title: Re: Crash prone 'modern roundabouts'
Post by: Sykotyk on April 10, 2016, 09:29:15 PM
How would it jam up the approaches anymore than they already are? More than one can be in a roundabout at the same time. But, only one approach at a time in rotation should get to go.

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they must wait until the first car at each other approach also clears the roundabout. And THEN they get to go. Same as a stop sign.

I'm glad you can operate the quote function. Again, 'How would it jam up the approaches anymore than they already are?' If a roundabout were so crowded to have traffic lined up at all four approaches, wouldn't you want traffic to be orderly, or are you content with 'every man for themselves'?
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on April 10, 2016, 10:43:27 PM
How would it jam up the approaches anymore than they already are? More than one can be in a roundabout at the same time. But, only one approach at a time in rotation should get to go.

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they must wait until the first car at each other approach also clears the roundabout. And THEN they get to go. Same as a stop sign.

I'm glad you can operate the quote function. Again, 'How would it jam up the approaches anymore than they already are?' If a roundabout were so crowded to have traffic lined up at all four approaches, wouldn't you want traffic to be orderly, or are you content with 'every man for themselves'?

I would have them operate the way they operate now, which is generally fine.
Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on April 11, 2016, 08:09:16 AM
[ Again, 'How would it jam up the approaches anymore than they already are?' If a roundabout were so crowded to have traffic lined up at all four approaches, wouldn't you want traffic to be orderly, or are you content with 'every man for themselves'?
If you have all 4 - or, worse, just 1 leg of roundabout flooded with traffic - you are outside design parameters, and things no longer work. Roundabouts are designed to be a somewhat ordered anarchy, when resources (time in the circle) are not managed, but shared. If one leg grabs 100% of time...
My personal record is sitting 15 minutes waiting for a gap in traffic. After some event was over, circle was flooded with south-to-north bumper to bumper traffic, and I was sitting on the eastern approach without a chance to do anything. Traffic light downstream ensured entire line moved at, or below, 15 MPH, so no gaps at all. I still have to see something like that for general commute, but that is  a probable failure mode for the concept.
Title: Re: Crash prone 'modern roundabouts'
Post by: kphoger on April 11, 2016, 01:55:28 PM
If there's already two cars ahead of you and a line at the other three approaches, you simply wait your turn. Not trying to remember whether you got to the intersection before someone else and go in that order.

Of course not.  But reaching the tail of the line of cars is not the same thing as getting to the intersection.  At a four-way stop, the only thing influencing your decision to go or wait is what's happening at the other three stop signs at that time.  Likewise, the only thing influencing your decision to go or wait is what's happening on your immediate left at that time.  That's what a stop sign means, and that's what a yield sign means.

And special circumstances require special decision-making.  An eighteen-wheeler, for example, can either make for more people going ahead of their turn (because he's very slow and waves you on, or because traffic needs to clear the intersection for his wide turn) or more people having to wait longer (because their line through the intersection has cleared while the truck is still turning, even though they got to the intersection after the cars that are still blocked).  The even traffic mentioned just up-thread by @kalvado should have paused every so often, even within the circulating roadway, to let him in; that's how polite drivers operate at a similar situation at a four-way stop, and that's how they should operate at a roundabout.

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Counter-clockwise, around and around until eventually the traffic is clear. * * * Again, if a roundabout is that congested, it should be cleared out similar to a four-way stop: traffic on the right goes first, counter-clockwise, until all the approaches are clear.

Actually, it's not that simple.  It's more efficient for each pair of opposing traffic to proceed at the same time, meaning NB and SB cars proceed through simultaneously, then EB and WB cars proceed through simultaneously, and so on.  In this scenario, four cars get through the intersection in only two "cycles" instead of four cycles.  However, this progression only works until, for example, SB is turning left and NB is turning right, then the sequence gets messed up.  There is no simple, perfect, optimal way of ordering the movements at a four-way stop, because different turning movements create different environments.

At a roundabout, it concerns me not one bit when the driver on the opposite side of the intersection got there or which direction he's going.  All that concerns me is what the driver immediately on my left is doing.

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At a round-about, there is no traffic pattern or rule other than 'yield to traffic in circle' which leaves a wide breadth as to how much space to yield. * * * And technically, if you're to yield to traffic in the circle, you have to yield to all traffic in the circle, not just whether you can floor it and get out in time before getting T-boned. Including oncoming traffic.

No more breadth than a yield sign at a simple four-way intersection.  All a yield sign indicates is that you give way to approaching traffic presenting an imminent danger; anything less than imminent is not your concern, because your paths do not conflict.  "Yield to traffic in circle" signage is simply the agency's way of explaining to drivers how a roundabout works, not that they have to wait for the entire circle to clear or some such nonsense.

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You get people gunning it to be the next one in the circle, regardless which 'turn' would've been there's at a stop sign. And then you get followers, who continue with the person in front of them. Which effectively becomes a four-phase traffic light with random phases.

These things happen at four-way stops too.  In neither intersection type, though, do followers make it "effectively become a four-phase traffic light with random phases", because those drivers are outliers and do not have any meaningful effect on the performance of the intersection.

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Modern roundabouts that are replacing intersections (small medians, not the large 100-200ft behemoths that I consider traffic circles or rotaries like in the northeast), work best on roads that handle intermittent traffic from all directions when traffic volumes generally don't clog up an intersection.

I agree.  I should point out that there are some roundabouts in areas of steady traffic that perform quite well, such as the Skaggs roundabout in Branson, Missouri.  That one is a five-leg roundabout that sees much more traffic on three of its approaches than on the other two, and both local and tourist traffic is a steady flow.  It performs great, and was a welcome replacement of what was there previously.

What I think seriously does a roundabout in is heavy traffic volumes, especially when there are traffic signals nearby.  Traffic tailbacks extending through a roundabout are like death to the intersection. 

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US 59 & US 169 in Garnett, Kansas is a decent example. Two roads with intermittent traffic. It's not steady from any one approach. It's better than signalized, and a lot better than a stop-sign. It works because the intersection never saw a pressing need for other action (four-lane with a median and at-grade ramp system with stop-signs to break up traffic). Most of the time, you'll approach that traffic circle and be the first to go through without impeding traffic from another direction.

Excellent example.  A similar four-way roundabout that functions great is the one on US-400 at Fredonia.  Pulling out onto 400 from the side road used to be a dangerous proposition, but now it's much safer without stoplights or stop signs.

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You put that roundabout in a downtown, urban, or suburban setting, and suddenly you get traffic. The roundabout doesn't relieve traffic, it only relieves wait times for a signal. But, enough traffic forces its wait time back to a signalized intersection.

Without nearby traffic signals, it should still be no problem.  Again, I think the killer in urban settings is nearby traffic signals.  Red-light tailbacks reaching the circulating roadway render the roundabout inoperable.  I hadn't much considered roundabout tailbacks reaching the stoplight, but that sort of thing happens with two stoplights anyway.  It's easier to get traffic to not block a signalized intersection than it is to get traffic to not block a whole roundabout.

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One thing roundabouts do, though, is create 'steady flow' for business and sidestreet traffic.

Imagine you're pulling out of a business that's just down the road from a traffic circle in a congested area. You constantly have traffic to deal with. Where, before, in a signalized intersection, you have a light that will temporarily block the flow of traffic before the turn phase begins for the perpendicular approaches.

This is true.  While it is risky business to plan on a break in heavy traffic due to signal timing (sometimes traffic is heavy enough that you never end up getting that gap you were hoping for), no such large gaps can be planned for with roundabouts.  This isn't a problem if traffic is light enough that small gaps emerge, but it does become a problem if traffic is heavy.  There's no easy way around this.

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Roundabouts/traffic circles have their place. But, a lot of them are being shoehorned into congested areas where they don't serve the need well.

This is true.  But it's also true of stop signs and traffic signals, added to locations where a roundabout would serve the need nicely.

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And a lot of that has to do with how drivers handle them. It's a free-for-all, rather than a traffic-control-device. We've seen it for decades with the YIELD sign at the end of on-ramps. Drivers do not heed them. Hell, there's many drivers you'll come across absolutely irate if you don't yield to the on-ramp traffic. That lack of respect and legality to a yield sign has carried over to the roundabout. That yield sign might as well not exist with how little people respect it.

As for yielding at an on-ramp merge...  Many jurisdictions don't even put yield signs at then end of the ramps.  Also, it is common courtesy to slow down or move over for merging traffic.  Basically, on-ramps are widely taken as more of a "form one lane" situation than a true yield situation, despite what signage might be present.  And, actually, this is a good thing:  having to come to a full stop upon merging onto a 65-mph highway is a recipe for disaster.

As for heeding yield signs in general, I agree that they are widely ignored, not just at on-ramps as discussed, but more dangerously at simple four-way intersections; drivers slow down so little for a simple yield intersection that, by the time a crossing vehicle comes into view, there's precious little time to actually stop.  But this is not what I've seen at roundabouts.  People approaching roundabouts are already slowing down due to additional signage and curve geometry, which makes them more ready to truly yield.  I honestly hardly ever see drivers blatantly ignoring yield signs at roundabout approaches the way I see them blatantly ignore them at simple four-way intersections.

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What they need is to remove the YIELD sign and replace it with a STOP sign and a white regulatory sign underneath that states something along the lines of, "For Traffic In Circle Only" similar in manner to how "Except Right Turn" gets placed under many stop signs where the through line turns right at an intersection.

Disagree.  Trying to fix a few bad drivers' behavior through more imperative signs is not going to solve anything.  What would likely result is a great number of drivers stopping for no reason:  by the time they're read the little white placard, they've already come to a full stop.  And then you'd still be left with your stated dilemma of what "in circle" means.  Will they remain stopped till the whole thing clears?  Etc.

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People, overwhelmingly, respect stop signs compared to yield signs. The lack of enforcement for "Failure To Yield" at a yield sign, anywhere, is astounding. At a stop sign, it's much more enforced. Which leads to compliance.

We can have a million and one 'Don't Text and Drive' or 'Don't Drink and Drive' but not one 'Yield means Yield' campaigns.

I'm not sure I've witnessed enough people running a yield sign with a police officer nearby to come to any conclusion about how often it's enforced.  And I'm pretty amazed that you have.  Generally, yield signs are used at low-volume intersections where running one doesn't usually put anyone in jeopardy and, in the case there is actual jeopardy, the chances of a cop being nearby are slim to none.  But whatever.
Title: Re: Crash prone 'modern roundabouts'
Post by: Sykotyk on April 12, 2016, 12:27:52 AM
I've seen it enough in a few places. And I've seen it cropping up at roundabouts. The definition of 'imminent' is the problem. Some drivers are a lot more brazen with their travel into the roundabout than others.

Yes, a STOP w/regulatory sign may cause some to stop without reason. But, there's enough scaredycats that do that as now with yield signs. But, it will slow down the people rolling through unsafely.

The uptick in accidents at these roundabouts is proving that drivers aren't driving properly through them. The issue whether the agencies responsible want to have their heads in the sand, or accept that some drivers simply bugger up the system. Both the timid and the brave.

The thing with signalized or 4-way, was that if you got a green light, your odds of not facing cross-traffic were next-to-nil. Sure, some ran lights. Either inattentive during the phase or the bastards who ran it just as their phase had ended, but it wasn't likely. In a 4-way, the traffic around you at least had to stop (unless, of course, inattentiveness at any point or trying to 'beat' someone through it). But, you had a better understanding of "if car from my left is cruising at 35mph up to a stop sign, and I just stopped at the stop sign, I may pause momentarily to make sure they, too, are stopping. At a yield situation, you're doing that while driving, and that other car may be thinking they can 'time' the roundabout to get through without stopping, or rather slowing down much, if at all.

Which comes down to the yield sign. It doesn't hold the weight in drivers' eyes as the stop sign does. It's the weak little brother to the stop sign.

Part of the allure of roundabouts is no more signals and the associated costs. But, flashing yellows at all approaches that can be turned to metered during heavy-volume situations would work best in major areas with sensors on the exits to show that the vehicle (or vehicles if a 4-way operating in tandem n/s e/w each) have cleared the roundabout.

But, then we'd be better off with a 4-way stop sign with a smaller geographic footprint.

Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on April 12, 2016, 10:40:27 AM
The uptick in accidents at these roundabouts is proving that drivers aren't driving properly through them. The issue whether the agencies responsible want to have their heads in the sand, or accept that some drivers simply bugger up the system. Both the timid and the brave.

I'm afraid you are putting things up side down: roundabouts are, by design, using controlled aggression to allow traffic to use smaller gaps and so increase throughput. So somewhat aggressive driving should be encouraged, not suppressed - otherwise capacity of roundabout would be reduced below meaningful threshold.
Title: Re: Crash prone 'modern roundabouts'
Post by: Sykotyk on April 13, 2016, 07:14:05 PM
The uptick in accidents at these roundabouts is proving that drivers aren't driving properly through them. The issue whether the agencies responsible want to have their heads in the sand, or accept that some drivers simply bugger up the system. Both the timid and the brave.

I'm afraid you are putting things up side down: roundabouts are, by design, using controlled aggression to allow traffic to use smaller gaps and so increase throughput. So somewhat aggressive driving should be encouraged, not suppressed - otherwise capacity of roundabout would be reduced below meaningful threshold.

I see roundabout as a traffic calming device. Sitting at a light or stop sign can be aggravating. Allowing a vehicle to proceed after only slowing down when there's inconsistent or little side traffic is the positive result of a roundabout.

Putting one in a heavily used intersection does what you say and what I had been pointing to for a while, that it takes away safety in exchange for the 'me first' attitude of drivers trying to be the next one into the circle or to avoid having to come to a full stop.

You've made my point.
Title: Re: Crash prone 'modern roundabouts'
Post by: english si on April 14, 2016, 04:16:14 AM
So somewhat aggressive driving should be encouraged, not suppressed - otherwise capacity of roundabout would be reduced below meaningful threshold.
Assertive, not aggressive. There's a big difference.

"the 'me first' attitude of drivers trying to be the next one into the circle or to avoid having to come to a full stop." - oddly we don't see that here: perhaps a cultural difference? But even in France (without the Germanic respect for rules, or the British love of queuing), Spain, etc they do it fine.
Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on April 14, 2016, 06:44:19 AM
So somewhat aggressive driving should be encouraged, not suppressed - otherwise capacity of roundabout would be reduced below meaningful threshold.
Assertive, not aggressive. There's a big difference.
Well, big question is what criteria should be used, and what kind of traffic that roundabout gets.
You want to be an assertive person who is going to wait until a gap big enough to keep 2 second intervals both before and after your car? Remember to take a tent and a grill, you will be camping there for a while.
I still think that being able to put a razor between two bumpers is not safe enough? I am with you... But I am evolving....

Once again, problem is with understanding the role of roundabouts. As I say, it's a problem- specific medication, Insulin should not be prescribed for every pneumonia.  Over here roundabouts are positioned as a replacement for heaviest load intersections. You plainly have no choice once you have a roundabout with 20-30k daily traffic count - you need to lower you threshold.
Title: Re: Crash prone 'modern roundabouts'
Post by: english si on April 14, 2016, 08:29:29 AM
You want to be an assertive person who is going to wait until a gap big enough to keep 2 second intervals both before and after your car? Remember to take a tent and a grill, you will be camping there for a while.
No I don't. Aggressive is "Poop, poop, out my way!", jumping onto a roundabout and expecting else everyone to make it safe, whereas assertive is "Hello, I'm here!". You don't need to slot into a 4 second gap as
1) The car in front of you won't hit you if you are a couple of yards behind it - you simply move slowly enough to make the gap bigger.
2) The car behind you can also slow down to make the gap bigger
3) Cars are turning off anyway and roundabouts are small enough that the person you are slotting in behind will have left the roundabout not long after you joined (unless turning right).
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Over here roundabouts are positioned as a replacement for heaviest load intersections.
I take it you've never been to the UK! We use them for far busier junctions than the the US. The 3 trunk road dual carriageway arms at the Black Cat Roundabout in Bedfordshire (the 4th arm is the old route of one of the trunk roads) have volumes of 53267 (north), 27784 (west) and 24977 (south), giving total figures of over 53k using that roundabout! OK, that's an outlying excessive case, but 20k-30k is very much par for the course.
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You plainly have no choice once you have a roundabout with 20-30k daily traffic count - you need to lower you threshold.
My nearest roundabout (a mini roundabout) has that sort of volume (and is far from a busy one for Blighty).* The gaps seem to be fine. I can't be bothered to time them, but they are about every two seconds. People just navigate the junction slowly, but assertively.


*3 arms with conservative (count would increase if the points were closer to the roundabout) 2014 figures of 14164, 16818 and 9610, divided by 2 (as each car through the roundabout would be counted twice) = 20296. There's roundabouts in my town with figures of 41899, 31830 (three arms) and 31610, and even they are rather ordinary for the UK. The 3-arm one between the A355 and A40 just north of M40 J2 has more than 43k vehicles per day and never seems to have any problems.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on April 14, 2016, 10:06:12 AM
English_si, are any of those UK roundabouts that you referenced signalized?  I have heard that at some of the bigger UK roundabouts have signals that are dark for most of the day but cycle during peak times. 
Title: Re: Crash prone 'modern roundabouts'
Post by: english si on April 14, 2016, 01:22:35 PM
The Black Cat was recently, but wasn't when the traffic figures were taken in 2014. I gather the signalisation merely extended the queues.

None of the others are signalised.
Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on April 14, 2016, 09:17:43 PM
No I don't. Aggressive is "Poop, poop, out my way!", jumping onto a roundabout and expecting else everyone to make it safe, whereas assertive is "Hello, I'm here!". You don't need to slot into a 4 second gap as
1) The car in front of you won't hit you if you are a couple of yards behind it - you simply move slowly enough to make the gap bigger.
2) The car behind you can also slow down to make the gap bigger
3) Cars are turning off anyway and roundabouts are small enough that the person you are slotting in behind will have left the roundabout not long after you joined (unless turning right).

OK, looks like we have a different definition of "aggressive".
I wouldn't call "Poop, poop, out my way!" aggressive, I would call that "idiot" at best (I am not sure if moderators would tolerate full comment).
Your assumption that the car behind you may slow down a bit _is_ the definition of "somewhat aggressive" for me, as "yield" assumes other driver should not have to touch brake pedal at all.
With that in mind, looks like we're on the same page here, but you're a more seasoned roundabouter...
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on April 15, 2016, 05:34:29 PM
Top 5 Crash-Prone Intersections In Oakland County Include 2 Roundabouts
http://detroit.cbslocal.com/2016/01/05/top-5-dangerous-intersections-in-oakland-county-include-2-roundabouts/

With 116 total crashes, the roundabout at M-5 & Pontiac Trail was the highest crash prone intersection in Oakland County in 2015.  The roundabout was constructed in 2011 and Oakland County drivers have had 4 years to get use to the operation of the roundabout.  Here is 10 years of crash data for this intersection based on SEMCOG crash data:

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/M5rb_zpsg1k4muyb.png)

Accidents at M-5 & Pontiac Trail jumped from 54 in 2014 to 116 in 2015.  Haggerty Road which runs parallel to M-5 was reconstructed in 2015 and the roundabout was part of the detour route.  This could help explain the large spike in accidents.
Title: Re: Crash prone 'modern roundabouts'
Post by: Sykotyk on April 17, 2016, 02:00:32 AM
The data should also be based on a percentage of total average daily vehicles that use that intersection. If a big development was built nearby or the roads around it were improved to make it a more preferable route, could see an uptick in traffic and then a corresponding uptick in accidents.

Detour traffic could easily explain the spike for 2015, though, as you have people unfamiliar with a road trying to follow orange blazers back to their original route or destination leaving them less observant at a roundabout.
Title: Re: Crash prone 'modern roundabouts'
Post by: kphoger on April 17, 2016, 08:10:05 AM
It also makes me wonder about the spike between 2011 and 2012.

I remember when I-57 northbound was closed in southern Illinois one, and all traffic was routed through the uncontrolled town square in Benton. Utter misery. A modern roundabout in that case would have helped not one bit; what was needed was traffic cops directing traffic.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on April 18, 2016, 10:54:33 AM
The data should also be based on a percentage of total average daily vehicles that use that intersection.

I previously listed crash rates for 3x2 and 2x2 multi-lane roundabouts I could find data on.  It’s important to note that many agencies consider a crash rate above 2.0 MEV as “critical” that warrants further investigation. 

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/crashrate_zpsglb8qh4x.png)

The average crash rate for these multi-lane roundabouts was 3.69 MEV.  As a comparison, the average crash rate of Minnesota’s high speed signalized intersections was just 0.8 MEV.  The multi-lane roundabouts have a crash rate over 4X higher than Minnesota’s high speed signalized intersections.
 
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/MNUntitled_zpsnrgwvaog.png)
http://www.dot.state.mn.us/trafficeng/publ/fundamentals/MnDOT_Safety_Handbook_FINAL.pdf
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on April 20, 2016, 02:23:08 PM
I think I'll leave this here ...

http://www.mlive.com/news/ann-arbor/index.ssf/2016/04/road_commission_improves_state.html#incart_river_home

Number of crashes at State and Ellsworth roundabout drops following initial spike

It's getting better.  The idiots are beginning to learn how to navigate it.  And it's not nearly as bad as someone who does not live here makes it out to be.  I have to deal with it every day, and have yet to see an accident.  I don't think anyone has died there, either.

It’s like bragging your favorite baseball team lost 9-2 when the day before they got shut out 14-0.   YAY… good job… only 114 crashes this year. 
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on April 21, 2016, 11:38:27 PM
Find out which Livingston County intersections rank highest for number of injuries
http://www.livingstondaily.com/story/news/local/community/livingston-county/2015/11/23/livingston-countys-worst-intersections-crashes/75170418/

Instead of ranking intersections by total crashes, the above article ranks them by the number of injuries.  Lee Road roundabout (pictured below) was No. 2 on the list with 23 injury crashes and 264 total crashes over the past 5 years.  There are literally hundreds of intersections in Livingston County.  If roundabouts are so much safer, how is it that the Lee Road roundabout had the 2nd highest number of injury crashes over the past 5 years? 

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/roundabout_double_zps5g1j0uxh.jpg)
Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on April 22, 2016, 08:00:07 AM
Find out which Livingston County intersections rank highest for number of injuries
http://www.livingstondaily.com/story/news/local/community/livingston-county/2015/11/23/livingston-countys-worst-intersections-crashes/75170418/
You know, it makes some sense to include exact location with a post like this one... here you go:
https://www.google.com/maps/place/Lee+Rd,+Brighton,+MI+48116/@42.5061734,-83.7604905,1154m/data=!3m1!1e3!4m2!3m1!1s0x88234fcef7c20dfb:0x53f7c294fdc4524a

I really wonder if traffic volumes warranted such a complex interchange set to begin with...
Title: Re: Crash prone 'modern roundabouts'
Post by: Tarkus on April 23, 2016, 01:12:12 AM
The engineer who designed that Lee Road dual-roundabout has to be some sort of sadist.  Honestly, it makes the Swindon Magic Roundabout look sensible. 
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on April 23, 2016, 09:06:55 AM
Look at how worn the pavement markings are in the below aerial compared to when Lee Road roundabout was freshly painted.  A lot of the safety improvements done to these crash prone roundabouts involve pavement marking tweaks.  All this research is done regarding pavement markings at roundabouts but then we allow the pavement markings to fade to nothing.

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/LeeoldUntitled_zpsv14pqthy.png)
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/roundabout_double_zps5g1j0uxh.jpg)
Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on April 23, 2016, 11:03:33 AM
Look at how worn the pavement markings are in the below aerial compared to when Lee Road roundabout was freshly painted.  A lot of the safety improvements done to these crash prone roundabouts involve pavement marking tweaks.  All this research is done regarding pavement markings at roundabouts but then we allow the pavement markings to fade to nothing.
One thing I heard about roundabouts is that they are oh, so much cheaper to maintain, unlike  traffic lights which consume power and need bulbs change!
Given new LED traffic controls, sounds like we have a $100 solution for an $1 problem..

As for the intersection in question, with total of 5 roundabouts... I only wonder how much was the kickback.
Title: Re: Crash prone 'modern roundabouts'
Post by: Tarkus on April 23, 2016, 04:34:56 PM
One thing I heard about roundabouts is that they are oh, so much cheaper to maintain, unlike  traffic lights which consume power and need bulbs change!
Given new LED traffic controls, sounds like we have a $100 solution for an $1 problem..

The whole "maintenance cost" claim with signals vs. roundabouts was a load of hooey even before LEDs became commonplace in signals.  The usually cited savings figure is $5000/year, which means that for a $250,000 signal vs. a $2,500,000 roundabout, you're looking at 450 years before one reaches the break even point, and I doubt the roundabout is going to have a design life of 450 years.
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on April 23, 2016, 06:37:48 PM
One thing I heard about roundabouts is that they are oh, so much cheaper to maintain, unlike  traffic lights which consume power and need bulbs change!
Given new LED traffic controls, sounds like we have a $100 solution for an $1 problem..

The whole "maintenance cost" claim with signals vs. roundabouts was a load of hooey even before LEDs became commonplace in signals.  The usually cited savings figure is $5000/year, which means that for a $250,000 signal vs. a $2,500,000 roundabout, you're looking at 450 years before one reaches the break even point, and I doubt the roundabout is going to have a design life of 450 years.

The price of intersection modification is highly subjective. Not all roundabouts cost $2.5mil, and not all signals cost $250k.

The best example might be freeway/service road interchanges. The cost of widening a bridge over a freeway costs a lot more than installing roundabouts at the ramp termini.

FWIW, WSDOT cites an average annual signal maintenance cost of $8k: http://goo.gl/q3Q6Kh
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on April 25, 2016, 05:27:25 PM
DOT eyes crash-heavy roundabout on Eau Claire's south side

http://www.leadertelegram.com/News/Front-Page/2016/03/30/Crash-heavy-roundabout-eyed.html

The article states there has been 26 crashes at the roundabout between 2011 and 2015.  That equates to about 5 crashes a year.  That to me is not "crash heavy" especially considering the amount of traffic volume US 53 carries.  This is a multi-lane roundabout but it's a simpler 2x1 variety.  I guess they plan on adding rumble strips before the roundabout to slow traffic down and also mound the center island to make it more visible to approaching motorists.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on April 27, 2016, 01:18:24 PM
A 2016 report by the UMD National Transportation Center analyzed the safety of Arizona roundabouts.   Of the double-lane roundabouts analyzed there was a 68% increase in the average rate of accidents per million vehicles.  Also, there was an 8% decrease in the average rate of injuries per year per million vehicles.  The report came to the following conclusion:

Quote
In conclusion, single-lane roundabouts improved the safety of intersections. However, double-lane roundabouts reduced the safety of intersections. A decision needs to be made as to either remove double-lane roundabouts or find solutions on how to make these roundabouts safe, such as making geometric improvements or educating the public on how to use them.

http://ntc.umd.edu/sites/default/files/documents/Publications/NTC2015-SU-R-3_Mamlouk.pdf

Many multi-lane roundabouts in this thread (specifically 2x2 and higher) have seen large increases in total accidents with a lackluster reduction in injury accidents.  This 2016 study of multi-lane roundabouts in Arizona match this performance.
Title: Re: Crash prone 'modern roundabouts'
Post by: JMAN_WiS&S on May 02, 2016, 12:36:31 PM
DOT eyes crash-heavy roundabout on Eau Claire's south side

http://www.leadertelegram.com/News/Front-Page/2016/03/30/Crash-heavy-roundabout-eyed.html

The article states there has been 26 crashes at the roundabout between 2011 and 2015.  That equates to about 5 crashes a year.  That to me is not "crash heavy" especially considering the amount of traffic volume US 53 carries.  This is a multi-lane roundabout but it's a simpler 2x1 variety.  I guess they plan on adding rumble strips before the roundabout to slow traffic down and also mound the center island to make it more visible to approaching motorists.
I mentioned this a few pages back and it seems people ignored it as nobody replied and continued other replies.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on May 02, 2016, 02:09:55 PM
DOT eyes crash-heavy roundabout on Eau Claire's south side

http://www.leadertelegram.com/News/Front-Page/2016/03/30/Crash-heavy-roundabout-eyed.html

The article states there has been 26 crashes at the roundabout between 2011 and 2015.  That equates to about 5 crashes a year.  That to me is not "crash heavy" especially considering the amount of traffic volume US 53 carries.  This is a multi-lane roundabout but it's a simpler 2x1 variety.  I guess they plan on adding rumble strips before the roundabout to slow traffic down and also mound the center island to make it more visible to approaching motorists.
I mentioned this a few pages back and it seems people ignored it as nobody replied and continued other replies.

I vaguely remember someone bringing up the US 53 Eau Claire roundabout but I didn’t see your earlier post until now.  My point is I don’t believe there is much of a crash problem at that Eau Claire roundabout (despite what the headline of the article leads you to believe).  I’ve been criticized for pointing out high crash rate roundabouts throughout this thread but I’ll be the first to defend a roundabout that is working well.  The multi-lane roundabout in Eau Claire averages about 5 crashes a year.  That doesn't sound bad at all.
Title: Re: Crash prone 'modern roundabouts'
Post by: JMAN_WiS&S on May 04, 2016, 12:12:18 PM
DOT eyes crash-heavy roundabout on Eau Claire's south side

http://www.leadertelegram.com/News/Front-Page/2016/03/30/Crash-heavy-roundabout-eyed.html

The article states there has been 26 crashes at the roundabout between 2011 and 2015.  That equates to about 5 crashes a year.  That to me is not "crash heavy" especially considering the amount of traffic volume US 53 carries.  This is a multi-lane roundabout but it's a simpler 2x1 variety.  I guess they plan on adding rumble strips before the roundabout to slow traffic down and also mound the center island to make it more visible to approaching motorists.
I mentioned this a few pages back and it seems people ignored it as nobody replied and continued other replies.

I vaguely remember someone bringing up the US 53 Eau Claire roundabout but I didn’t see your earlier post until now.  My point is I don’t believe there is much of a crash problem at that Eau Claire roundabout (despite what the headline of the article leads you to believe).  I’ve been criticized for pointing out high crash rate roundabouts throughout this thread but I’ll be the first to defend a roundabout that is working well.  The multi-lane roundabout in Eau Claire averages about 5 crashes a year.  That doesn't sound bad at all.
The only issue is people going into it too quickly going SB. I'm quite suprised eau claire only has a couple roundabouts and not more, as it seems they are popular elsewhere in the state.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on May 04, 2016, 01:26:40 PM
Looking at an aerial of the US 53 Eau Claire roundabout it’s not surprising there aren’t many crashes.  Scully Drive services a Gander Mountain (a big store, but that’s the only traffic being generated) and Old Town Hall Road has some small businesses along it.  There just isn’t much conflict at this roundabout as the majority of traffic is continuing straight on US 53.

https://www.google.com/maps/@44.7643843,-91.4200398,787m/data=!3m1!1e3
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on May 04, 2016, 01:49:30 PM
JMAN, do you have any word on how many crashes there have been at the roundabout at Highway 124 and Business 29 outside Chippewa Falls?  It was constructed around 2009 and replaced a full-blown interchange.  There are slip lanes for all legs which should reduce the conflicts inside the roundabout itself.  Any experience with this roundabout?

https://www.google.com/maps/@44.9210902,-91.3808932,259m/data=!3m1!1e3
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on May 04, 2016, 01:50:43 PM
Looking at an aerial of the US 53 Eau Claire roundabout it’s not surprising there aren’t many crashes.  Scully Drive services a Gander Mountain (a big store, but that’s the only traffic being generated) and Old Town Hall Road has some small businesses along it.  There just isn’t much conflict at this roundabout as the majority of traffic is continuing straight on US 53.

https://www.google.com/maps/@44.7643843,-91.4200398,787m/data=!3m1!1e3


On a side note, interesting stripping for the off ramp there, even though there's no left turn movement.  Usually those lanes would be stripped to 'guide' people into a right turn.  Looking back on the GSV I can understand it during construction...7 years ago.   But no reason not to have revised it since.

The on-ramp isn't much better, as if it was meant for traffic to turn left onto it.

https://goo.gl/maps/qybfKukfA992

Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on May 04, 2016, 02:08:09 PM
Looking at an aerial of the US 53 Eau Claire roundabout it’s not surprising there aren’t many crashes.  Scully Drive services a Gander Mountain (a big store, but that’s the only traffic being generated) and Old Town Hall Road has some small businesses along it.  There just isn’t much conflict at this roundabout as the majority of traffic is continuing straight on US 53.

https://www.google.com/maps/@44.7643843,-91.4200398,787m/data=!3m1!1e3


On a side note, interesting stripping for the off ramp there, even though there's no left turn movement.  Usually those lanes would be stripped to 'guide' people into a right turn.  Looking back on the GSV I can understand it during construction...7 years ago.   But no reason not to have revised it since.

The on-ramp isn't much better, as if it was meant for traffic to turn left onto it.

https://goo.gl/maps/qybfKukfA992

I can understand the off-ramp. Sometimes, if there isn't sufficient merge area, it's better to have a right-angle "yield" (though I don't agree with the stop sign seen here -- something like this is what I prefer: https://goo.gl/UTjZjj).

The on-ramp though...it's not something I haven't seen before, but it's certainly not something I prefer.
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on May 04, 2016, 02:55:08 PM
Looking at an aerial of the US 53 Eau Claire roundabout it’s not surprising there aren’t many crashes.  Scully Drive services a Gander Mountain (a big store, but that’s the only traffic being generated) and Old Town Hall Road has some small businesses along it.  There just isn’t much conflict at this roundabout as the majority of traffic is continuing straight on US 53.

https://www.google.com/maps/@44.7643843,-91.4200398,787m/data=!3m1!1e3


On a side note, interesting stripping for the off ramp there, even though there's no left turn movement.  Usually those lanes would be stripped to 'guide' people into a right turn.  Looking back on the GSV I can understand it during construction...7 years ago.   But no reason not to have revised it since.

The on-ramp isn't much better, as if it was meant for traffic to turn left onto it.

https://goo.gl/maps/qybfKukfA992

I can understand the off-ramp. Sometimes, if there isn't sufficient merge area, it's better to have a right-angle "yield" (though I don't agree with the stop sign seen here -- something like this is what I prefer: https://goo.gl/UTjZjj).

The on-ramp though...it's not something I haven't seen before, but it's certainly not something I prefer.

I was referring to the fact the left yellow line goes straight into the intersection, with a straight stop bar to boot.  At least the stop bar is angled towards the right of the lane, but in reality the whole stop bar should be angled, with the yellow line curving to the right as well.
Title: Re: Crash prone 'modern roundabouts'
Post by: JMAN_WiS&S on May 05, 2016, 12:21:32 PM
JMAN, do you have any word on how many crashes there have been at the roundabout at Highway 124 and Business 29 outside Chippewa Falls?  It was constructed around 2009 and replaced a full-blown interchange.  There are slip lanes for all legs which should reduce the conflicts inside the roundabout itself.  Any experience with this roundabout?

https://www.google.com/maps/@44.9210902,-91.3808932,259m/data=!3m1!1e3
I have driven and ridden through that one before, not sure on crash stats, the intersection is fairly self explanatory. I find it cool how you can still see row grading where the old sb-> eb flyover ramp used to be.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on May 26, 2016, 03:05:42 PM
The infamous 50/60 Lakeville roundabout has had another crash recently.  This time a women and 3 of her kids had to be extricated from an Escalade after it flipped over on it's side.  This is the same roundabout that saw 44 crashes in the first two months of operation back in 2015:

http://sunthisweek.com/2016/04/15/woman-children-pulled-from-lakeville-rollover-crash/
Title: Re: Crash prone 'modern roundabouts'
Post by: dvferyance on May 27, 2016, 02:13:39 PM
Simple answer the roundabouts on Moorland Rd in New Berlin by I-43. They could be the worst in the country.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on May 27, 2016, 03:34:26 PM
^Here is a dated article discussing the Moorland Road roundabouts at I-43.  At that time (2008 data) the Moorland Road/Rock Ridge roundabout had the highest crash rate of any other major intersection in New Berlin.  The article goes on to state that the number of injury accidents is way down.  This is a total fabrication.  What the article is looking at is the severity of accidents at the roundabout and not total injury accidents…. 

Quote
While there are more accidents at the roundabout, the number of injury accidents is way down… Of the 44 reportable and nonreportable accidents at Rock Ridge/Moorland in a 15-month period from the end of 2007 through January 2009, only three were injury accidents, he said. That is far lower than the seven out of 13 accidents that were injury accidents at the Rock Ridge and Moorland intersection with traffic lights, Rieder said. Those 13 accidents happened over a period of seven years.
http://www.newberlinnow.com/news/56607067.html

Just look at the data the article cites:
Before roundabout (7 years of crash data):   13 total crashes; 7 injury crashes 
After roundabout (15-months of crash data):  44 total crashes; 3 injury crashes

How can this article claim that the number of injury accidents is way down?  We are comparing 15-months of post-roundabout crash data to 7 years of pre-roundabout crash data.  If you actually average it out by injury crashes per year, injury crashes have more than doubled (going from 1 injury crashes/year before the roundabout to 2.4 injury crashes/year after the roundabout).
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on May 27, 2016, 04:07:02 PM
^^

Not sure why any of that matters today. No doubt they may be stretching the numbers a little, but the numbers are still old and irrelevant.. I'd love to see some new data on those roundabouts.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on May 27, 2016, 04:54:34 PM
For the record, I don’t believe the Moorland Road roundabouts are performing that badly.  A crash rate of 2.0 MEV (which is cited in the article) is right on the cusp of being considered a satisfactory crash rate.  There are roundabouts with crash rates much higher than the Moorland Road roundabouts that would concern me more.  Interchange roundabouts, for whatever reason, seem to have lower crash rates than non-interchange roundabouts and that could explain why Moorland Road roundabouts are performing OK.  I definitely wouldn’t consider it the worst in the country. 

All that said, that New Berlin article is a powder puff propaganda piece by trying to claim that injury accidents are WAY down at the roundabout. 
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on May 27, 2016, 08:15:17 PM
For the record, I don’t believe the Moorland Road roundabouts are performing that badly.  A crash rate of 2.0 MEV (which is cited in the article) is right on the cusp of being considered a satisfactory crash rate.  There are roundabouts with crash rates much higher than the Moorland Road roundabouts that would concern me more.  Interchange roundabouts, for whatever reason, seem to have lower crash rates than non-interchange roundabouts and that could explain why Moorland Road roundabouts are performing OK.  I definitely wouldn’t consider it the worst in the country.

There's also the point that the northern roundabout is exceptionally large, much larger than any modern roundabout I've seen before. I'm sure that has something to do with it as well (visibility being one of them).

All that said, that New Berlin article is a powder puff propaganda piece by trying to claim that injury accidents are WAY down at the roundabout.

I would guess that the author didn't quite understand the topic.
Title: Re: Crash prone 'modern roundabouts'
Post by: dvferyance on May 28, 2016, 09:44:52 AM
For the record, I don’t believe the Moorland Road roundabouts are performing that badly.  A crash rate of 2.0 MEV (which is cited in the article) is right on the cusp of being considered a satisfactory crash rate.  There are roundabouts with crash rates much higher than the Moorland Road roundabouts that would concern me more.  Interchange roundabouts, for whatever reason, seem to have lower crash rates than non-interchange roundabouts and that could explain why Moorland Road roundabouts are performing OK.  I definitely wouldn’t consider it the worst in the country. 

All that said, that New Berlin article is a powder puff propaganda piece by trying to claim that injury accidents are WAY down at the roundabout.
There are still problems no doubt. Some mornings traffic backs up on to I-43 I have seen this not once but several times. The SB Moorland turn to Rock Ridge is a nightmare and very confusing. I had a very close call there not too long ago. What bothers me the most is nobody in New Berlin wanted it the DOT should have respected the wishes of the people. After all it's us the residents of New Berlin that have to deal with it not the DOT engineers that were pushing for it. While I am unaware of the crash rates now there I can say there is getting to be more traffic than what they can handle. And when more development kicks in to the south watch out.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on June 07, 2016, 10:59:59 PM
A local morning show spent a half hour today talking about the crash prone roundabouts in metro Detroit. 

http://www.mediafire.com/download/w2h1dd0n8xey7de/06072016podcastpart1_cutted2.mp3
Title: Re: Crash prone 'modern roundabouts'
Post by: AlexandriaVA on June 07, 2016, 11:23:23 PM
But were they modern? I was going to chalk the accidents up to Midwestern simpletons, but if the fine folks of Indiana can figure out roundabouts, what's holding back Michiganers?
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on June 08, 2016, 07:59:54 AM
^A similar naïve comment was made early on in this thread:
Speaks more to the (in)flexibility of Michigan drivers than it does any inherent safety risk with roundabouts.  New roundabouts elsewhere have seen major drops in the number of crashes.

Crash prone roundabouts throughout the country have been discussed on this thread.  The roundabout at 116th Street & Keystone in Carmel, Indiana has a very high crash rate.  Keep in mind the majority of Carmel roundabouts are either single lane or the simplified 1x2 variety.  The few complex 2x2 roundabouts Carmel do have high crash rates.
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/crashrate_zpsglb8qh4x.png)
Title: Re: Crash prone 'modern roundabouts'
Post by: nhoward45 on June 09, 2016, 10:23:07 AM
The term "roundabout" is merely rebranding for the older term, traffic circle.   These were nuisances and traffic hazards in the 1940s and 1950s, and in many areas were replaced with grade separated interchanges or bypassed with freeways.  Traffic circles may be OK in a low speed residential environment, but are dangerous in any heavily trafficked area.  Traffic signals may slow down vehicle flow, but are less risky than traffic circles.  Rebranding changes nothing.  A garbage man is a garbage man, even if rebranded a sanitary engineer.

This is not a regional issue either.  The list of high risk traffic circles includes Southern, Western, Northeastern, and Canadian locations as well as Midwestern ones.
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on June 09, 2016, 11:20:48 AM
The term "roundabout" is merely rebranding for the older term, traffic circle.   These were nuisances and traffic hazards in the 1940s and 1950s, and in many areas were replaced with grade separated interchanges or bypassed with freeways.  Traffic circles may be OK in a low speed residential environment, but are dangerous in any heavily trafficked area.  Traffic signals may slow down vehicle flow, but are less risky than traffic circles.  Rebranding changes nothing.  A garbage man is a garbage man, even if rebranded a sanitary engineer.

This is not a regional issue either.  The list of high risk traffic circles includes Southern, Western, Northeastern, and Canadian locations as well as Midwestern ones.

Let me know when you're done spouting nonsense. Not a single thing you just wrote is even remotely accurate.
Title: Re: Crash prone 'modern roundabouts'
Post by: kphoger on June 09, 2016, 01:30:31 PM
The term "roundabout" is merely rebranding for the older term, traffic circle.   These were nuisances and traffic hazards in the 1940s and 1950s, and in many areas were replaced with grade separated interchanges or bypassed with freeways.  Traffic circles may be OK in a low speed residential environment, but are dangerous in any heavily trafficked area.  Traffic signals may slow down vehicle flow, but are less risky than traffic circles.  Rebranding changes nothing.  A garbage man is a garbage man, even if rebranded a sanitary engineer.

This is not a regional issue either.  The list of high risk traffic circles includes Southern, Western, Northeastern, and Canadian locations as well as Midwestern ones.

Let me know when you're done spouting nonsense. Not a single thing you just wrote is even remotely accurate.

Since you, nhoward45, appear to be a new member, let's make this clearer for you.  A modern roundabout must meet specific design criteria, the most important two being flared approaches and yield upon entry.  These two criteria were certainly not universally implemented in the 1940s and 1950s.

And risk can be analyzed in two ways:  total crashes or severity of crashes.  Roundabouts tend to increase the number of total crashes but diminish the severity of those crashes.  This topic is actually sort of about how good of a job they do at this.  What it looks like, offhand, is that you just jumped into page 19 of a discussion without reading the rest of it.
Title: Re: Crash prone 'modern roundabouts'
Post by: nhoward45 on June 09, 2016, 01:31:26 PM
Please explain the difference between traffic circles or roundabouts.

If traffic circles/roundabouts were such a great idea, please explain why highway engineers in last four decades of the 20th Century replaced or bypassed them. 

In Texas, the Harry Hines traffic circle in Dallas was replaced by grade separation at the intersection.  Traffic circles in Fort Worth and Lubbock were bypassed through the construction of Interstate highways. 
Title: Re: Crash prone 'modern roundabouts'
Post by: Rothman on June 09, 2016, 01:48:53 PM
Somebody forgot to do their homework.

http://safety.fhwa.dot.gov/intersection/innovative/roundabouts/
Title: Re: Crash prone 'modern roundabouts'
Post by: kphoger on June 09, 2016, 02:27:48 PM
Please explain the difference between traffic circles or roundabouts.
There's a Google for that. (http://bfy.tw/6Bm5)

Quote
If traffic circles/roundabouts were such a great idea, please explain why highway engineers in last four decades of the 20th Century replaced or bypassed them.
Because older-style traffic circles had safety issues.  As traffic counts increased, these problems increased in significance.

Quote
Traffic circles in Fort Worth and Lubbock were bypassed through the construction of Interstate highways.
Bypassed or replaced?  If they were bypassed, then that would mean the traffic circles are still there.  If they were replaced, then...well, obviously, since Interstates are freeways, and freeways don't have cross-traffic.
Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on June 09, 2016, 02:51:39 PM
Somebody forgot to do their homework.

http://safety.fhwa.dot.gov/intersection/innovative/roundabouts/

I love to compare roundabouts to an insulin: can be a lifesaver, but needs to be used properly - and definitely not an omnicure.
But unlike insulin, roundabouts are advertised as such...
Title: Re: Crash prone 'modern roundabouts'
Post by: US 81 on June 10, 2016, 05:14:19 PM

...
Quote
Traffic circles in Fort Worth and Lubbock were bypassed through the construction of Interstate highways.
Bypassed or replaced?  If they were bypassed, then that would mean the traffic circles are still there.  If they were replaced, then...well, obviously, since Interstates are freeways, and freeways don't have cross-traffic.

"Bypassed" is correct for Ft. Worth. Lubbock's was replaced during construction of I-27.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on June 13, 2016, 09:20:51 PM
Bo and Luke Duke were driving around Romania. 

Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on June 14, 2016, 10:44:26 PM
I'm not sure whether or not this study has been linked here, or not (I don't believe it has); for the sake of the following comment, let's presume it has not been.

Back in 2002, several FHWA employees visited Sweden, Germany, the Netherlands, and the UK to study different traffic signal/control schemes practised in each of those countries. One of the biggest takeaways from this visit was the roundabout. Though roundabouts had already been built in the US, there hadn't been much official documentation on them (hence why it took until 2009 to develop marking and design standards). Throughout the document, the FHWA employees note that roundabouts are effective at reducing the severity of collisions, but not the number of collisions:

Quote from: Chapter 9, summary
4. Promote roundabouts as alternatives to signalized intersections as a way to manage the consequences of collisions (severity versus frequency).
Quote from: Chapter 2, Sweden
...The primary focus is on crash severity, not frequency....On the basis of this principle, SNRA has converted signalized intersections to roundabouts, recognizing that the frequency of total accidents may increase, but the severity of those accidents may be greatly reduced.
Quote from: Chapter 3, Sweden
When high-accident locations have been identified, progressive solutions are developed...In some cases, where accident severity is high, Sweden has removed traffic signals and replaced them with roundabouts, recognizing that overall accident rates may increase and line-of-sight may be degraded, but the rate of severe (fatal and injurious) accidents will decrease...In urban areas, unsignalized roundabouts can have a negative systemwide effect because it is difficult to control and manage platooning and traffic progression.

And, on severity alone:

Quote from: Chapter 5, the Netherlands
The turbo roundabout...is used in the Netherlands to eliminate weaving conflicts found in standard multilane roundabouts...This low-speed configuration also has been found to allow a higher capacity than the standard two-lane roundabout. While a standard roundabout has 16 potential conflict points, the turbo roundabout has 10. In either case, the conflict points are low speed, and the resulting accidents are typically less severe than those at signalized intersections (Figure 5-5).

There are additional comments -- you can read the study here: http://goo.gl/6MQq2Z

I do wonder why initial studies were so focused on demonstrating the reduction of collisions, versus the severity. I know both were part of the studies, but at least as far as I can tell, the biggest plus of roundabouts is the reduction in severity, not any sort of reduction of overall collisions.

I don't doubt the benefits of the roundabout. It's pretty obvious that roundabouts reduce the severity of collisions, but, the sheer number of collisions at a given intersection doesn't seem to have any connection to the geometric design of said intersection. There are some signals with a lot of collisions, and some roundabouts with a lot of collisions. Equally, there are some signals with very few collisions, and some roundabouts with very few collisions.

tl;dr: the primary benefit of the roundabout is reduced severity.
Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on June 14, 2016, 11:01:08 PM

I do wonder why initial studies were so focused on demonstrating the reduction of collisions, versus the severity. I know both were part of the studies, but at least as far as I can tell, the biggest plus of roundabouts is the reduction in severity, not any sort of reduction of overall collisions.
[...]
tl;dr: the primary benefit of the roundabout is reduced severity.

My strong impression is that primary advantage of roundabouts in US is ability to get more money into construction contracts, and who cares what bullshit is used to justify that to the crowd.
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on June 14, 2016, 11:23:40 PM

I do wonder why initial studies were so focused on demonstrating the reduction of collisions, versus the severity. I know both were part of the studies, but at least as far as I can tell, the biggest plus of roundabouts is the reduction in severity, not any sort of reduction of overall collisions.
[...]
tl;dr: the primary benefit of the roundabout is reduced severity.

My strong impression is that primary advantage of roundabouts in US is ability to get more money into construction contracts, and who cares what bullshit is used to justify that to the crowd.

I'm not usually convinced by conspiracies....this is not an exception.
Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on June 14, 2016, 11:47:39 PM

I do wonder why initial studies were so focused on demonstrating the reduction of collisions, versus the severity. I know both were part of the studies, but at least as far as I can tell, the biggest plus of roundabouts is the reduction in severity, not any sort of reduction of overall collisions.
[...]
tl;dr: the primary benefit of the roundabout is reduced severity.

My strong impression is that primary advantage of roundabouts in US is ability to get more money into construction contracts, and who cares what bullshit is used to justify that to the crowd.

I'm not usually convinced by conspiracies....this is not an exception.

Not a conspiracy, just plain old corruption. Which is just business as usual.
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on June 15, 2016, 12:23:04 AM

I do wonder why initial studies were so focused on demonstrating the reduction of collisions, versus the severity. I know both were part of the studies, but at least as far as I can tell, the biggest plus of roundabouts is the reduction in severity, not any sort of reduction of overall collisions.
[...]
tl;dr: the primary benefit of the roundabout is reduced severity.

My strong impression is that primary advantage of roundabouts in US is ability to get more money into construction contracts, and who cares what bullshit is used to justify that to the crowd.

I'm not usually convinced by conspiracies....this is not an exception.

Not a conspiracy, just plain old corruption. Which is just business as usual.

Right...corruption. Got it m8.

Anyone here interested in discussing roundabouts?
Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on June 15, 2016, 12:26:41 AM

Right...corruption. Got it m8.

Anyone here interested in discussing roundabouts?
Sure. Are there any estimates on demolition costs for those?
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on June 15, 2016, 12:38:25 AM

Right...corruption. Got it m8.

Anyone here interested in discussing roundabouts?

Sure. Are there any estimates on demolition costs for those?

Never heard of such a thing. Maybe tradephoric has some idea.
Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on June 15, 2016, 12:54:26 AM

Right...corruption. Got it m8.

Anyone here interested in discussing roundabouts?

Sure. Are there any estimates on demolition costs for those?

Never heard of such a thing. Maybe tradephoric has some idea.

Which is actually a big problem of those roundabouts. There is no clear understanding why they should be built; once studies showing how great those are turn out irrelevant, there is a different argument. There is no understanding of when roundabouts actually work best; I didn't see realistic estimates of throughput. There is no understanding of future costs - such as demolition. 
Two things are known for sure: that they must be built, and how much they cost. I can see two reasons for that:  corruption in financing construction and old good stupidity.
If I have to choose which one is more realistic, I definitely choose both.
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on June 15, 2016, 02:08:54 AM

Right...corruption. Got it m8.

Anyone here interested in discussing roundabouts?

Sure. Are there any estimates on demolition costs for those?

Never heard of such a thing. Maybe tradephoric has some idea.

Which is actually a big problem of those roundabouts. There is no clear understanding why they should be built; once studies showing how great those are turn out irrelevant, there is a different argument. There is no understanding of when roundabouts actually work best; I didn't see realistic estimates of throughput. There is no understanding of future costs - such as demolition. 
Two things are known for sure: that they must be built, and how much they cost. I can see two reasons for that:  corruption in financing construction and old good stupidity.
If I have to choose which one is more realistic, I definitely choose both.

Whoa whoa whoa, slow down partner. You asked me about demolition costs ... I told you I didn't know ... then you respond with some rambling, incoherent paragraph, darting from point to point, apparently at random, only to arrive at an indecipherable conclusion ("If I have to choose which one...I definitely choose both.").

I've never had to ask someone to do this before, but...please re-write your post. I want to be able to reply with a decent response, but I simply don't understand what you're saying.
Title: Re: Crash prone 'modern roundabouts'
Post by: english si on June 15, 2016, 04:27:16 AM
I've never had to ask someone to do this before, but...please re-write your post. I want to be able to reply with a decent response, but I simply don't understand what you're saying.
Seems to be saying that the crab people thrust roundabouts on us, without telling us the costs of demolishing them when we inevitably (and kalvado does think it's inevitable for some reason) see through the crab people's arguments that we need them and so that's a hidden cost of building them - the cost of demolishing the blighters when we find them shite.
Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on June 15, 2016, 08:07:46 AM

Whoa whoa whoa, slow down partner. You asked me about demolition costs ... I told you I didn't know ... then you respond with some rambling, incoherent paragraph, darting from point to point, apparently at random, only to arrive at an indecipherable conclusion ("If I have to choose which one...I definitely choose both.").

I've never had to ask someone to do this before, but...please re-write your post. I want to be able to reply with a decent response, but I simply don't understand what you're saying.
[/quote]

OK, same thing in a more formalized basis.

1. Current altitude to roundabouts (RA) among traffic engineers is based on faith, not on fact.
1a. When initial research on how great RA are proved wrong, a new set of "they are still great!" texts emerged.
1b. There are still no serious research regarding applicability of RA in terms of handleable traffic volumes, types of roads where RA can work best (2x2 lane discussion in this thread)  etc.
1c. Some official recommendation pushing RA as first choice are reinforcing religious altitude
1d. No understanding of full lifecycle costs; despite declared low-maintenance, things like re-training snow plow drivers and improvising and relocating pedestrian crosswalks after construction "because we're on learning curve", as well as costs of demolition of messy structure are not taken into account on decision making stage.
1e. I really doubt that organization, which is extremely busy with defining types of fonts to be used on signs, has enough technical expertise to develop understanding such complex system.

2. Cost of building roundabout is significant and mostly out of public control since there is little basis for comparison.
2a. That attracts construction companies, since MONEY. Visibly same structure can cost $0.5M and $2M within 20 miles radius (local example)
2b. That attracts politicians, since that allows to flow money in a non-transparent way.

Harsh? definitely. True? At least partially.   
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on June 15, 2016, 08:17:34 AM

2. Cost of building roundabout is significant and mostly out of public control since there is little basis for comparison.
2a. That attracts construction companies, since MONEY. Visibly same structure can cost $0.5M and $2M within 20 miles radius (local example)
2b. That attracts politicians, since that allows to flow money in a non-transparent way.

None of this is unique to roundabouts.  An intersection replacement costs can vary widely, depending on what needs to be done.  And there's a ton of basis of comparison...they know how much land they need, they know the various costs.  They can do an analysis of the cost of an intersection vs. the cost of a roundabout, along with ongoing maintenance and electricity costs.  All of this is pretty typical stuff.

Many states puts these projects out to bid, and there's plenty of contractors out there willing to bid on the projects.  Again, much of this can be found online. 
Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on June 15, 2016, 08:36:25 AM

2. Cost of building roundabout is significant and mostly out of public control since there is little basis for comparison.
2a. That attracts construction companies, since MONEY. Visibly same structure can cost $0.5M and $2M within 20 miles radius (local example)
2b. That attracts politicians, since that allows to flow money in a non-transparent way.

None of this is unique to roundabouts.  An intersection replacement costs can vary widely, depending on what needs to be done.  And there's a ton of basis of comparison...they know how much land they need, they know the various costs.  They can do an analysis of the cost of an intersection vs. the cost of a roundabout, along with ongoing maintenance and electricity costs.  All of this is pretty typical stuff.

Many states puts these projects out to bid, and there's plenty of contractors out there willing to bid on the projects.  Again, much of this can be found online.

NYSDOT tend to publish lump sum costs and nothing more than that. As for bidding... This is something what is likely to lend our governor either in jail or in the White house in near future. You just have to do it right!
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on June 15, 2016, 09:20:31 AM

2. Cost of building roundabout is significant and mostly out of public control since there is little basis for comparison.
2a. That attracts construction companies, since MONEY. Visibly same structure can cost $0.5M and $2M within 20 miles radius (local example)
2b. That attracts politicians, since that allows to flow money in a non-transparent way.

None of this is unique to roundabouts.  An intersection replacement costs can vary widely, depending on what needs to be done.  And there's a ton of basis of comparison...they know how much land they need, they know the various costs.  They can do an analysis of the cost of an intersection vs. the cost of a roundabout, along with ongoing maintenance and electricity costs.  All of this is pretty typical stuff.

Many states puts these projects out to bid, and there's plenty of contractors out there willing to bid on the projects.  Again, much of this can be found online.

NYSDOT tend to publish lump sum costs and nothing more than that. As for bidding... This is something what is likely to lend our governor either in jail or in the White house in near future. You just have to do it right!


BidX is your friend when it comes to all things bidded on about roads.  If you're maintain a thought process that includes everything the state does is evil and corrupt though, it's not going to be of any help.  There are rules that are generally followed, with few exceptions.

For NY: https://www.bidx.com/ny/main
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on June 15, 2016, 10:14:55 AM
It's pretty obvious that roundabouts reduce the severity of collisions
The severity index is simply a weighted average of fatal, injury, and PDO crashes.   Here is the formula from the FHWA:

Severity Index = (12 * F + 3 * I + 1 * PDO) / N
Where: 
F=total number of fatal crashes
I =total number of injury crashes
N = total number of crashes

Let’s figure out the severity index of a multi-lane roundabout with the following stats:
AADT=40,000
Fatal crashes = 0
Injury crashes = 10
PDO crashes = 90
Total crashes = 100
Severity Index = (12 * 0 + 3 * 10 + 1 * 90) / 100  =  1.2

Now what is the severity index of a signalized intersection with the following stats:
AADT=40,000
Fatal crashes = 0
Injury crashes = 10
PDO crashes = 30
Total crashes = 40
Severity Index = (12 * 0 + 3 * 10 + 1 * 30) / 40 = 1.5

Sure, the roundabout had a lower severity of crashes but does that make it safer?  You have to consider the frequency of crashes to determine if the reduction in severity is actually leading to fewer injury crashes.  Stating that “roundabouts reduce the severity of crashes” is just a clever way to mask the fact that roundabouts aren’t always safer (IE. some 2x2 multi-lane roundabouts). 
Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on June 15, 2016, 10:43:08 AM

BidX is your friend when it comes to all things bidded on about roads.  If you're maintain a thought process that includes everything the state does is evil and corrupt though, it's not going to be of any help.  There are rules that are generally followed, with few exceptions.

For NY: https://www.bidx.com/ny/main
Thank you for the reference, will look at it later...
As about  state=evil.. not difficult in a state which lost couple of top leaders to federal prisons in a past year and governor shedding all his friends in attempt not to join the gang. But if you will, the root cause is unclear technical justification strongly supported at political level. I don't remember that level of support for SPUI, for example - probably because advantages become clear after single-digit drives through one of those.
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on June 15, 2016, 06:32:31 PM
Stating that “roundabouts reduce the severity of crashes” is just a clever way to mask the fact that roundabouts aren’t always safer (IE. some 2x2 multi-lane roundabouts).

There is no perfect, winner-take-all design. There are examples of every type of intersection with both a lot, and very few collisions. I specified this in my original post:

I don't doubt the benefits of the roundabout. It's pretty obvious that roundabouts reduce the severity of collisions, but the sheer number of collisions at a given intersection doesn't seem to have any connection to the geometric design of said intersection. There are some signals with a lot of collisions, and some roundabouts with a lot of collisions. Equally, there are some signals with very few collisions, and some roundabouts with very few collisions.

My point was simply that roundabouts, as a whole, have a better severity record. There are inexplicable exceptions, of course, but, they're exceptions.

And to be clear, to tie this back into your original post way back yonder, there are certainly some discrepancies in the FHWA's original studies. But, roundabouts are still pretty damn good at protecting from severe, life-threatening injuries, simply because their design makes such collisions rather difficult (unless of course you drive straight over the middle, like in Carmel, IN).

My post (http://www.aaroads.com/forum/index.php?topic=15546.msg2151711#msg2151711), at the top of this page, was to bring up what I thought was an interesting discrepancy (the FHWA knew full well that roundabouts don't always decrease collisions, but they still heavily marketed roundabouts with that tagline anyway).
Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on June 15, 2016, 07:42:43 PM

My post (http://www.aaroads.com/forum/index.php?topic=15546.msg2151711#msg2151711), at the top of this page, was to bring up what I thought was an interesting discrepancy (the FHWA knew full well that roundabouts don't always decrease collisions, but they still heavily marketed roundabouts with that tagline anyway).

And even reduced severity is a poor metrics. If that was the ultimate one, reducing speed limit on interstates to 25 MPH should be a no-brainer.
\
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on June 16, 2016, 12:40:58 AM

My post (http://www.aaroads.com/forum/index.php?topic=15546.msg2151711#msg2151711), at the top of this page, was to bring up what I thought was an interesting discrepancy (the FHWA knew full well that roundabouts don't always decrease collisions, but they still heavily marketed roundabouts with that tagline anyway).

And even reduced severity is a poor metrics. If that was the ultimate one, reducing speed limit on interstates to 25 MPH should be a no-brainer.

Not in my opinion. Two cars bumping into each other at 80 is safer than a car going 50 rear-ending a car going 25. Which is to say, set speed limits closest to where the majority of cars are going the same speed (lack of differential = less severe collisions).
Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on June 16, 2016, 09:34:01 AM

My post (http://www.aaroads.com/forum/index.php?topic=15546.msg2151711#msg2151711), at the top of this page, was to bring up what I thought was an interesting discrepancy (the FHWA knew full well that roundabouts don't always decrease collisions, but they still heavily marketed roundabouts with that tagline anyway).

And even reduced severity is a poor metrics. If that was the ultimate one, reducing speed limit on interstates to 25 MPH should be a no-brainer.

Not in my opinion. Two cars bumping into each other at 80 is safer than a car going 50 rear-ending a car going 25. Which is to say, set speed limits closest to where the majority of cars are going the same speed (lack of differential = less severe collisions).

And you realize that 56% of fatalities occur in single-vehicle accidents?
(putting on traffic engineer hat) to reduce severity of such accidents on freeways, speed of free flowing traffic must be reduced to match that with the new speed limit. traffic calming measures may include lane narrowing and possibly chicanes. While increasing travel times and severely hurting US economy, these measures would allow increased ticket revenue and would reduce crash severity for single vehicle accidents and number of fatalities. Safety first!
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on June 17, 2016, 09:26:05 AM
My point was simply that roundabouts, as a whole, have a better severity record. There are inexplicable exceptions, of course, but, they're exceptions.

Prince Fielder of the Texas Rangers is batting .197 and having a pretty abysmal year.  Brett Eibner of the Kansas City Royals is batting .471 and is lighting it up.  Can you predict who has more hits?  Prince Fielder is having a bad year but he still has 39 more hits than Eibner (since Eibner only has 17 at bats vs. Fielder’s 238). 

You can have a lot more hits (ie. injury crashes) when you get more at bats (ie. frequency of crashes).  You admit that there is discrepancies in the FHWA's studies yet continue to regurgitate the misleading stats that they cite.  Sure, we can be clapping seals and say how great roundabouts are because they have low severity crashes.  But there should be some focus that at some of these 2x2 multi-lane roundabouts, the frequency of crashes has been abysmally high (leading to injury crashes).

Aren't roundabouts great!
(https://media.giphy.com/media/hDwYu8UEcUone/giphy.gif)
Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on June 17, 2016, 01:30:18 PM
  You admit that there is discrepancies in the FHWA's studies yet continue to regurgitate the misleading stats that they cite.  Sure, we can be clapping seals and say how great roundabouts are because they have low severity crashes. 

That is actually what I call indoctrination. Studies may be flawed, but we know the Truth!
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on June 17, 2016, 07:23:54 PM
You can have a lot more hits (ie. injury crashes) when you get more at bats (ie. frequency of crashes).

So, let me get this straight: roundabouts that had more collisions after installation, also had an increase in injuries (in every case)?? ......

You admit that there is discrepancies in the FHWA's studies yet continue to regurgitate the misleading stats that they cite.  Sure, we can be clapping seals and say how great roundabouts are because they have low severity crashes.  But there should be some focus that at some of these 2x2 multi-lane roundabouts, the frequency of crashes has been abysmally high (leading to injury crashes)

The problem is that there has been very little formal follow-up to the FHWA's initials studies. Some DOT's have investigated before-and-after situations, sometimes finding that the roundabouts resulted in far more collisions than anticipated, but there hasn't been, at least to my knowledge, any sort of legit follow-up, covering the whole of the nation's roundabouts. We've cherry-picked some roundabouts in this thread, but we both know this thread isn't any sort of official study (although I will admit, as I already have dozens of times, that the FHWA's initial studies might be a little off).
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on June 20, 2016, 08:45:12 AM
The problem is that there has been very little formal follow-up to the FHWA's initials studies. Some DOT's have investigated before-and-after situations, sometimes finding that the roundabouts resulted in far more collisions than anticipated, but there hasn't been, at least to my knowledge, any sort of legit follow-up, covering the whole of the nation's roundabouts. We've cherry-picked some roundabouts in this thread, but we both know this thread isn't any sort of official study (although I will admit, as I already have dozens of times, that the FHWA's initial studies might be a little off).

I agree that more studies need to be done.  I already suggested a study that should be published...

This would be an eye opening study if it were published:

“The Safety Performance of Roundabouts with Average Daily Traffic exceeding 30,000”


The 30,000 ADT condition would weed out single-lane roundabouts and most 2x1 multi-lane roundabouts.  The focus would be nearly entirely on the safety performance of 2x2 (or higher) roundabouts in America. Ideally, the study would analyze interchange and non-interchange roundabouts separately and come up with two different sets of safety numbers.


Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on June 20, 2016, 05:36:14 PM
The problem is that there has been very little formal follow-up to the FHWA's initials studies. Some DOT's have investigated before-and-after situations, sometimes finding that the roundabouts resulted in far more collisions than anticipated, but there hasn't been, at least to my knowledge, any sort of legit follow-up, covering the whole of the nation's roundabouts. We've cherry-picked some roundabouts in this thread, but we both know this thread isn't any sort of official study (although I will admit, as I already have dozens of times, that the FHWA's initial studies might be a little off).

I agree that more studies need to be done.  I already suggested a study that should be published...

This would be an eye opening study if it were published:

“The Safety Performance of Roundabouts with Average Daily Traffic exceeding 30,000”


The 30,000 ADT condition would weed out single-lane roundabouts and most 2x1 multi-lane roundabouts.  The focus would be nearly entirely on the safety performance of 2x2 (or higher) roundabouts in America. Ideally, the study would analyze interchange and non-interchange roundabouts separately and come up with two different sets of safety numbers.


I suspect hourly traffic may be even more important. There are efforts on stretching commute hours - staged shifts, etc - to reduce hourly traffic while maintaining total number of vehicles.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on June 22, 2016, 07:59:26 AM
Pontiac Trail roundabout most accident-prone in Michigan

An Oakland County intersection is named the most-accident prone in Michigan.  The roundabout at Pontiac Trail and M-5 in Commerce Township had 186 crashes last year.  That's 54 more than any other intersection in the state. Coming in at number two was Telegraph and 12 Mile in Southfield while Eleven Mile and Van Dyke in Warren -- placing third.

http://www.fox2detroit.com/news/local-news/154684840-story
Title: Re: Crash prone 'modern roundabouts'
Post by: 7/8 on June 27, 2016, 12:52:28 PM
Waterloo Region (in Ontario) has dozens of roundabouts, but there is one that has an especially high collision rate; the roundabout at Homer Watson and Block Line in Kitchener.
http://www.therecord.com/opinion-story/6127192-the-record-s-view-this-roundabout-must-be-fixed-at-homer-watson-boulevard-and-block-line-road-in-ki/ (http://www.therecord.com/opinion-story/6127192-the-record-s-view-this-roundabout-must-be-fixed-at-homer-watson-boulevard-and-block-line-road-in-ki/)

Quote
There were 51 collisions at the roundabout in 2011, the year it opened. That number crept upward the next year, when 53 collisions were recorded, then soared in 2013 when there were 72 collisions.

To its credit, the region responded by changing signs, altering lanes and lowering speeds in the vicinity. The result? There were 107 collisions at the roundabout in 2014 — one every three or four days and more than double the number in 2012.

It originally had 3 lanes on one side, but after a bus hit one of my classmates at my high-school, they decided to close the third lane off. They also reduced the speed limit by 20 km/h, but most people ignore that and it hasn't improved the collision rate.

I personally like using roundabouts, but I think it would help a lot if more people would use their signals when exiting.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on June 27, 2016, 02:08:07 PM
Manufacturers are designing bulky a-pillar in a quest to receive five star safety ratings.  Do bulky A-pillar designs reduce driver visibility and lead to drivers pulling out into the roundabout thinking it’s clear when it’s not?  The curves of a roundabout can make it easy for a vehicle to get lost in the a-pillar.

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/A-pillars_zpsrp1ucgda.jpg)
http://www.safespeed.org.uk/bike005.pdf
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on June 27, 2016, 02:17:18 PM
Manufacturers are designing bulky a-pillar in a quest to receive five star safety ratings.  Do bulky A-pillar designs reduce driver visibility and lead to drivers pulling out into the roundabout thinking it’s clear when it’s not?  The curves of a roundabout can make it easy for a vehicle to get lost in the a-pillar.

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/A-pillars_zpsrp1ucgda.jpg)
http://www.safespeed.org.uk/bike005.pdf


Trebek: Over-exaggerations for $3 please?

And just wondering...why is the picture taken as if the driver is sitting in the middle of the front, rather than in front of the steering wheel?
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on June 27, 2016, 03:52:58 PM
^I agree that "Killer Pillars" is over the top. 

That said, the point is still valid.  Just today i was approaching a roundabout and my a-pillar was blocking the view of a white pickup circulating through the roundabout.  I started to pull out infront of them just as they appeared from my a-pillar's "blind spot".  Luckily i was able to stop in time and no harm was done.  It was the first time i realized that my a-pillar was blocking the view of a circulating vehicle and i instantly took note of the scenario.  I was diligently scanning for circulating vehicles, but that white pickup still came out of nowhere to me.  It's not that i wasn't looking.     

Now the Monday morning quarterbacks will suggest a million different things i should have done to keep myself out of that scenario.  Ultimately, i feel like I almost got in an accident because i can't see through steel.  If I come to a complete stop before entering and turn my head from left-to-right to ensure a vehicle isn't in my a-pillar blind spot, then you get impatient drivers on the verge of rear-ending you because you aren't entering the roundabout fast enough for them.  If you just go assuming nobody is in your a-pillar blind spot, you risk pulling out infront of someone.  Honeslty, i'll piss off people behind me and let them rear end me before I pull out infront of a white-pickup again.
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on June 27, 2016, 05:43:50 PM
I've had large A-pillars block me from seeing pedestrians about to cross, other vehicles when pulling out at a t-junction, literally anything when pulling straight out of a parking spot (after having backed in, which I do quite often). At roundabouts? Sure, but not any more often than at any other type of junction.
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on June 27, 2016, 05:56:44 PM
I've had large A-pillars block me from seeing pedestrians about to cross, other vehicles when pulling out at a t-junction, literally anything when pulling straight out of a parking spot (after having backed in, which I do quite often). At roundabouts? Sure, but not any more often than at any other type of junction.

Exactly.  Blind spots are hardly unique to roundabouts. 
Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on June 27, 2016, 07:44:43 PM
I've had large A-pillars block me from seeing pedestrians about to cross, other vehicles when pulling out at a t-junction, literally anything when pulling straight out of a parking spot (after having backed in, which I do quite often). At roundabouts? Sure, but not any more often than at any other type of junction.

Exactly.  Blind spots are hardly unique to roundabouts.

They are somewhat unique with respect to angles  being unusual. On "normal" intersection, 99% of cases traffic comes from exact left and exact right. There is a certain habit of looking for those directions, known head positions  - I don't know those positions but my body does.
A somewhat similar situation is (also roundabout related) a newly constructed merge to arterial - road was rerouted due to roundabout. I drive that spot every day, and it took me quite a while to get used to new alignment. I am not alone, I just witnessed a close call at the location with bus having to move half a lane to avoid collision.
Problem is that ramp merges to road in a curve, and main road traffic is in unusual spot somewhere between 7 and 8 o'clock - neither over the shoulder, nor in the mirror. Lots of drivers cut off main road traffic without seeing it...

I would say this is same effect.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on June 27, 2016, 08:45:58 PM
The blue line represents a vehicle path that may be in the blind spot of someone waiting to enter the roundabout.  The angles present at a roundabout can make it pretty easy for a vehicle to get lost in the a-pillar.

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/A-pillar_zpszhee5qnz.png)

The most logical alternative to the roundabout pictured above would be a signaled intersection.  It’s true that blind spots are hardly unique to roundabouts.  Here’s another revelation … traffic is controlled by blinky lights at a signalized intersection.  The potential dangers of blind spots at signalized intersections can be alleviated by the use of traffic control devices (ie. no turn on red signs, protected only left turns, conflicting vehicle movements never come on together in the phasing, etc.).  You don’t have the same control at a free-flowing roundabout (you just got to live with the crashes). 
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on June 27, 2016, 09:05:52 PM
The blue line represents a vehicle path that may be in the blind spot of someone waiting to enter the roundabout.  The angles present at a roundabout can make it pretty easy for a vehicle to get lost in the a-pillar.

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/A-pillar_zpszhee5qnz.png)

The most logical alternative to the roundabout pictured above would be a signaled intersection.  It’s true that blind spots are hardly unique to roundabouts.  Here’s another revelation … traffic is controlled by blinky lights at a signalized intersection.  The potential dangers of blind spots at signalized intersections can be alleviated by the use of traffic control devices (ie. no turn on red signs, protected only left turns, conflicting vehicle movements never come on together in the phasing, etc.).  You don’t have the same control at a free-flowing roundabout (you just got to live with the crashes). 


You're fucking kidding me, right? You're looking out the drivers door window, inches from ones face. I've been driving in circles and roundabouts all my life, and not once have I ever had such a gastrically huge blind spot.
Title: Re: Crash prone 'modern roundabouts'
Post by: Brian556 on June 28, 2016, 12:27:38 AM
I don't think this should be a problem. It is very easy to see, and you and always lean forward if nessessary.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on June 28, 2016, 05:42:52 PM
Experimental fencing has been installed at the crash prone roundabout of M-5 & Pontiac Trail in an effort to slow drivers down.  According to the article, the average speed of traffic coming off is 30-33 mph.  They want it to be 18-23 mph.  What does everyone think of this idea? 

http://www.wxyz.com/news/region/oakland-county/drivers-have-mixed-feelings-about-new-fences-at-m-5-roundabout 
Title: Re: Crash prone 'modern roundabouts'
Post by: kphoger on June 28, 2016, 05:56:15 PM
Experimental fencing has been installed at the crash prone roundabout of M-5 & Pontiac Trail in an effort to slow drivers down.  According to the article, the average speed of traffic coming off is 30-33 mph.  They want it to be 18-23 mph.  What does everyone think of this idea? 

http://www.wxyz.com/news/region/oakland-county/drivers-have-mixed-feelings-about-new-fences-at-m-5-roundabout 

Not in favor.  Reduce visibility to improve safety?  Not cool.  Driver speed through a roundabout should be controlled by geometry; in this case, I'd say they need to both flare the approaches and reduce the ICD.
Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on June 28, 2016, 06:06:35 PM
Experimental fencing has been installed at the crash prone roundabout of M-5 & Pontiac Trail in an effort to slow drivers down.  According to the article, the average speed of traffic coming off is 30-33 mph.  They want it to be 18-23 mph.  What does everyone think of this idea? 

http://www.wxyz.com/news/region/oakland-county/drivers-have-mixed-feelings-about-new-fences-at-m-5-roundabout 

Not in favor.  Reduce visibility to improve safety?  Not cool.  Driver speed through a roundabout should be controlled by geometry; in this case, I'd say they need to both flare the approaches and reduce the ICD.

That is a common problem of roundabouts as far as I can tell: when it is being built, it is cheap, it is efficient, it is maintenance-free
And then reality kicks in. Need to add crosswalk signals, rebuild approaches, add lighting, improve pedestrian and bike safety, provide additional training for snow plow drivers - and additional hours for them...   
How often they would need to replace those mesh fences - every two weeks?
Title: Re: Crash prone 'modern roundabouts'
Post by: kphoger on June 28, 2016, 06:15:07 PM
Experimental fencing has been installed at the crash prone roundabout of M-5 & Pontiac Trail in an effort to slow drivers down.  According to the article, the average speed of traffic coming off is 30-33 mph.  They want it to be 18-23 mph.  What does everyone think of this idea? 

http://www.wxyz.com/news/region/oakland-county/drivers-have-mixed-feelings-about-new-fences-at-m-5-roundabout 

Not in favor.  Reduce visibility to improve safety?  Not cool.  Driver speed through a roundabout should be controlled by geometry; in this case, I'd say they need to both flare the approaches and reduce the ICD.

That is a common problem of roundabouts as far as I can tell: when it is being built, it is cheap, it is efficient, it is maintenance-free
And then reality kicks in. Need to add crosswalk signals, rebuild approaches, add lighting, improve pedestrian and bike safety, provide additional training for snow plow drivers - and additional hours for them...   
How often they would need to replace those mesh fences - every two weeks?

I'm curious to know when the roundabout in question was constructed.  The engineers should have known better than to build that large of an ICD and that straight of approaches if it was constructed in the last decade.
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on June 28, 2016, 07:04:15 PM
Experimental fencing has been installed at the crash prone roundabout of M-5 & Pontiac Trail in an effort to slow drivers down.  According to the article, the average speed of traffic coming off is 30-33 mph.  They want it to be 18-23 mph.  What does everyone think of this idea? 

http://www.wxyz.com/news/region/oakland-county/drivers-have-mixed-feelings-about-new-fences-at-m-5-roundabout 

Not in favor.  Reduce visibility to improve safety?  Not cool.  Driver speed through a roundabout should be controlled by geometry; in this case, I'd say they need to both flare the approaches and reduce the ICD.

That is a common problem of roundabouts as far as I can tell: when it is being built, it is cheap, it is efficient, it is maintenance-free
And then reality kicks in. Need to add crosswalk signals, rebuild approaches, add lighting, improve pedestrian and bike safety, provide additional training for snow plow drivers - and additional hours for them...   
How often they would need to replace those mesh fences - every two weeks?

That stuff is generally taken care of in the planning process.

I drive a snowplow for a state.  We've never been given any additional training for roundabouts or circles. They are just another piece of asphalt that we have to clear snow from.

Again, this tells me that we're just making up excuses why roundabouts shouldn't be built, rather than using any actual concrete evidence why roundabouts shouldn't be built.  Again, every once in a while traditional intersections undergo modifications as well after they are constructed due to unforeseen events.  And snowplowing...training for a roundabout?  Ha!
Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on June 28, 2016, 07:37:44 PM

I drive a snowplow for a state.  We've never been given any additional training for roundabouts or circles. They are just another piece of asphalt that we have to clear snow from.
And that is exactly why extra training is needed. Because that one incoming lane flares into two lanes for different roundabout lanes. So how many plow passes are required to clean that approach? Exactly, three passes because approach is 2 lanes + gore wide.
Some heroic plow drivers do two passes, leaving approximately 1.5 driving lane and then designed flow pattern is not completely screwed up.  Not really a problem since that snow usually melts in a month or so, but still.

And yes, this tells me that even DOTs have no understanding of how roundabouts work.. But hey, this is just a second decade of learning curve!
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on June 28, 2016, 07:52:52 PM
I'm curious to know when the roundabout in question was constructed.  The engineers should have known better than to build that large of an ICD and that straight of approaches if it was constructed in the last decade.

The approaches seem to have plenty of flair. You could add chicanes, like they do here in Washington, and all over Australia, but many drivers simply ignore the lane lines, drifting all over the place, in an attempt to keep up a high speed. The best way to slow down drivers, is to have them slow down naturally....

The wide visibility really is the biggest issue here. Roundabouts can have high-speeds, but only once you're in the circle...entering speeds need to be much lower. Not so low that a stop sign is the preferred method, but low enough that T-bone collisions don't suddenly become features of roundabouts.

High entry speeds are generally the result of good visibility. While that sounds like a good thing, driver's need to be giving way at or near the yield line, not 400 feet before the roundabout (in other words, you need to decide whether or not you can enter based on conditions present within 20 to 30 feet of the yield line). Because driver's had such excellent visibility, they were deciding whether or not they could enter well before reaching the circle ... some drivers, apparently, chose poorly.

If you decrease the size of the decision-making zone, entry speeds should decrease, because drivers will need to slow down to confirm that they can enter (the smaller size of this zone will naturally result in lower speeds).

The good news is that, if this is successful (which I'm sure it will be), the county will be installing more permanent decoration, such as bushes).

(http://i.imgur.com/FOAQ274.png)
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on June 28, 2016, 09:05:00 PM
The M-5/Pontiac Trail roundabout saw a big spike in crashes in 2015.  It just so happens the roundabout was part of a major detour route in 2015 during the Haggerty Road closure.  The traffic patterns the roundabout was exposed to during the detour didn’t match the traffic patterns the roundabout was designed for.  Sure, roundabouts can work well under specific scenarios, but when the moon and stars don’t align you can get into trouble.   

My concern is any report dealing with the effectiveness of the experimental fencing will be biased towards comparing 2015 to 2016 crash data.  That to me won’t be a fair comparison.   People will think the fencing is effective simply because there was a year over year drop in crashes.  Again, the traffic patterns at the roundabout during the detour last year doesn’t match the traffic patterns occurring during this experimental fencing test.  That’s a huge point that shouldn’t be ignored.
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on June 29, 2016, 12:15:19 AM

I drive a snowplow for a state.  We've never been given any additional training for roundabouts or circles. They are just another piece of asphalt that we have to clear snow from.
And that is exactly why extra training is needed. Because that one incoming lane flares into two lanes for different roundabout lanes. So how many plow passes are required to clean that approach? Exactly, three passes because approach is 2 lanes + gore wide.
Some heroic plow drivers do two passes, leaving approximately 1.5 driving lane and then designed flow pattern is not completely screwed up.  Not really a problem since that snow usually melts in a month or so, but still.

And yes, this tells me that even DOTs have no understanding of how roundabouts work.. But hey, this is just a second decade of learning curve!

What?

You do understand I plow in a state with traffic circles wider than nearly any roundabout, and dealing not only with normal roads entering and exiting, but driveways and parking lots accessing the circle as well.

Circles are just like any other road feature. Put the plow down and push the snow. Spread salt to help melt the snow. Repeat as necessary.

There's an art to it. It takes time to clear a road, and keep it cleared. It's not like there's a wall of 20 inches of snow that traffic can't travel thru.  But with snow falli!g off vehicles, even a plowed road will become slushy again.

A 90 degree right turn at an intersection is worse. Those trucks don't turn on a dime, and snow sticks out far from the curb. Plow operators just keep going at it until it's acceptable.

Please...offer your services to plow a road. No doubt you'll do better than everyone else.
Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on June 29, 2016, 01:02:42 PM

What?

You do understand I plow in a state with traffic circles wider than nearly any roundabout, and dealing not only with normal roads entering and exiting, but driveways and parking lots accessing the circle as well.

Circles are just like any other road feature. Put the plow down and push the snow. Spread salt to help melt the snow. Repeat as necessary.

There's an art to it. It takes time to clear a road, and keep it cleared. It's not like there's a wall of 20 inches of snow that traffic can't travel thru.  But with snow falli!g off vehicles, even a plowed road will become slushy again.

A 90 degree right turn at an intersection is worse. Those trucks don't turn on a dime, and snow sticks out far from the curb. Plow operators just keep going at it until it's acceptable.

Please...offer your services to plow a road. No doubt you'll do better than everyone else.

Possibly things are much better in NJ; but roundabouts I deal with in NY often had 2/3 lane under  snow a week after snow ended.  At least that was the case during last winter, 2014/2015 (we didn't have any winter in 2015/2016).  I don't remember any problems with right turns except for barricades of snow pushed from  the main road blocking side roads/driveways. Once again, could be different vehicles used in different places.
And well, thing is turning around and doing another pass at roundabout approach seem less than straightforward. You either need to look for a u-turn spot, or back along curved approach. I am not sure if it is done really carefully
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on June 29, 2016, 01:12:03 PM
I'm curious to know when the roundabout in question was constructed.  The engineers should have known better than to build that large of an ICD and that straight of approaches if it was constructed in the last decade.

You seem to be implying that a smaller ICD would have been more effective at reducing the number of crashes.  To your original question, the M-5/Pontiac Trail roundabout was constructed in 2011.  While there was an increase in crashes after the roundabout was constructed, the crash rate wasn’t as high as other multi-lane roundabouts cited in this thread.  It wasn’t until 2015 when the roundabout had a big spike in crashes (likely due to it being part of a major detour route).  Now you are throwing the roundabout design under the bus because of an abnormally high number of crashes in 2015.  Yes, a roundabout that experiences 100 crashes in a year is a problem, but you are trying to convince me a smaller ICD would have done better.  I’m not buying it. 
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on June 29, 2016, 03:41:22 PM
A 3x2 roundabout at Superior & 14th in Lincoln, NE was constructed in 2012.  Due to the large increase in accidents, one of the circulating lanes was removed in 2013.  It is now a 2x1 roundabout.  In addition, they added fencing at all 4-approaches in 2014.  Now they are talking about spending $888,000 to add more permanent features to replace the "ugly" fencing.  I haven't read any reports indicating how effective the fencing was, but i'm assuming the roundabout saw a big drop in crashes simply because it went from a 3x2 to a 2x1 roundabout.

http://www.1011now.com/content/news/More-updates-likely-coming-to-14th--Superior-roundabout-373306771.html

Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on June 29, 2016, 05:53:38 PM
The problem is we don't know if the fencing was successful at the Lincoln, NE roundabout.  They compared the crash rate of the 3x2 roundabout with no fencing to the 2x1 roundabout with fencing.  I could have told you the crash rate would drop if you convert the roundabout to a simplified 2x1 roundabout.  But what effect did the fencing have?  We have no idea because they lumped in the lane configuration changes with the fence change.

Quote
When the 14th and Superior roundabout was initially built and opened to traffic the crash rate was higher than anticipated. We had the configuration of the initial roundabout studied and the results showed that we needed to reduce the number of lanes and also reduce the sight distance at the roundabout. One lane in each direction was removed with traffic control devices. The site distance was limited by constructing chain link fence with slats in the medians.

The devices have been in place for approximately two years. The results show that the crash rate has been reduced significantly by the lane reduction and the fencing. At this point we are moving ahead with making the temporary adjustments to the roundabout more permanent. Concept plans have been developed to show putting tack on median concrete in place of the lane reductions. This will allow us to remove the traffic control devices along the outer lanes. A landscaping plan was developed for the center island of the roundabout and the medians. The landscaping and a short decorative fence have been shown to take the place of the chain link fence.

Along with this work a piece of artwork will be loaned to the city from the Duncans to be placed in the center of the roundabout. Construction on the more permanent fixes for the roundabout could begin as early as Fall of 2016.
https://www.lincoln.ne.gov/city/pworks/projects/14th/superior-safety/
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on June 29, 2016, 09:27:53 PM
Venice is proposing changes to the crash prone roundabout at Jacaranda Blvd and Venice Avenue.  Since it’s completion in 2008, the roundabout has held the dubious distinction as being the top intersection for wrecks in Sarasota and Manatee Counties.  To combat this, FDOT plans on eliminating a circulating lane inside the roundabout.


Edit:  The proposed roundabout changes slated to cost $585,000 has been approved by the transportation agency.

http://www.wftv.com/news/florida/roundabout-changes-okdjacaranda-and-venice-avenue-intersection-deemed-high-crash-zonekd/332095543
Title: Re: Crash prone 'modern roundabouts'
Post by: kphoger on June 30, 2016, 08:53:33 PM
I'm curious to know when the roundabout in question was constructed.  The engineers should have known better than to build that large of an ICD and that straight of approaches if it was constructed in the last decade.

You seem to be implying that a smaller ICD would have been more effective at reducing the number of crashes.  To your original question, the M-5/Pontiac Trail roundabout was constructed in 2011.  While there was an increase in crashes after the roundabout was constructed, the crash rate wasn’t as high as other multi-lane roundabouts cited in this thread.  It wasn’t until 2015 when the roundabout had a big spike in crashes (likely due to it being part of a major detour route).  Now you are throwing the roundabout design under the bus because of an abnormally high number of crashes in 2015.  Yes, a roundabout that experiences 100 crashes in a year is a problem, but you are trying to convince me a smaller ICD would have done better.  I’m not buying it. 

My assertion is that the roundabout should be designed with a smaller ICD and more-flared approaches in order to reduce driver speed, which is what the fencing is supposed to accomplish.

The approaches do have some flare, but not enough. If a driver is physically able to enter the circulating roadway at such speeds, then the geometry of the roundabout is not doing its job. Approaches need to be flared enough that a driver cannot exceed the target speed upon entry. A smaller ICD does the same for vehicles already in the roadway; this, IMO, is a lesser issue but does contribute to a driver's perception as to whether or not it's OK to push the envelope.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on June 30, 2016, 10:29:35 PM
My assertion is that the roundabout should be designed with a smaller ICD and more-flared approaches in order to reduce driver speed, which is what the fencing is supposed to accomplish.

It seems like you can get more flare at larger diameter roundabouts.  If a roundabout is too small you are limited to how much you can flare the approach out (before you overshoot the circle so to speak).  I have a few other points why I believe larger ICD roundabouts may be more effective at reducing crashes:

#1. You don’t want the fastest path of a roundabout to resemble a straight line if your goal is to keep speeds down.  Which red line resembles a drag strip? 

Small ICD roundabout:
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/fastestpath_zpskfw1ywq5.jpg)

Large ICD roundabout:
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/largeICD2_zpsrqj98twj.png)

#2. Drivers have more reaction time when the approach legs of a roundabout are spread out.  Imagine CAR A enters the roundabout mistakenly believing CAR B is about to exit.  Would u want CAR B to take 1.7 seconds or 3.4 seconds to travel the blue path?  Now it’s true that the average circulating speeds might be SLIGHTLY higher at the larger ICD roundabout but the speeds wouldn’t be drastically different.  Instead of 3.4 seconds reaction time at the large ICD roundabout, it might really be 3 seconds because the car is circulating at 23 mph as opposed to 20 mph.  Still, would you want 1.7 second reaction time or 3 second reaction time when taking evasive action?

Small ICD roundabout:
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Test4_zpshnyyiesp.jpg)

Large ICD roundabout:
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Test3_zpscdfdzp4h.jpg)

#3.  Look at the empirical evidence.  The 2x2 multi-lane roundabouts with smaller central island diameters have a greater increase in crashes than the roundabouts with larger central island diameters:
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/RBDATASummary_zpsg7upbybr.png)

Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on June 30, 2016, 10:37:15 PM
One other point about the fencing idea.  Sure, you restrict the visibility of vehicles inside the roundabout but you also restrict the visibility of pedestrians inside the crosswalk (who are crossing the exit leg of the roundabout).  Is it really a good idea to restrict the visibility of pedestrians?
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on July 01, 2016, 12:53:01 AM
One other point about the fencing idea.  Sure, you restrict the visibility of vehicles inside the roundabout but you also restrict the visibility of pedestrians inside the crosswalk (who are crossing the exit leg of the roundabout).  Is it really a good idea to restrict the visibility of pedestrians?

I think it's better to hide the pedestrians until they are about to cross each carriageway. That way, overly-courteous drivers in the other carriageway don't stop too early. Use those yellow flashing beacons if visibility is truly an issue.
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on July 01, 2016, 07:49:20 AM
Fencing also keeps pedestrians crossing where they should be crossing, rather than jumping out into the street wherever they feel like.  Good for motorists too, as they shouldn't come upon a ped in a random part of the road. As long as the fence is 3 feet high or so, visibility isn't reduced for either peds or motorists.
Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on July 01, 2016, 09:26:38 AM
One other point about the fencing idea.  Sure, you restrict the visibility of vehicles inside the roundabout but you also restrict the visibility of pedestrians inside the crosswalk (who are crossing the exit leg of the roundabout).  Is it really a good idea to restrict the visibility of pedestrians?

I think it's better to hide the pedestrians until they are about to cross each carriageway. That way, overly-courteous drivers in the other carriageway don't stop too early. Use those yellow flashing beacons if visibility is truly an issue.
It's even better to hide pedestrians until they are past windshield.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 13, 2016, 11:33:21 AM
The Lee Road roundabout in Livingston County has been previously discussed on this thread.  It had the second highest number of INJURY crashes in Livingston County over the past 5 years and by far the highest number of total crashes.

http://www.livingstondaily.com/story/news/local/community/livingston-county/2015/11/23/livingston-countys-worst-intersections-crashes/75170418/

The Livingston County Road Commission is now considering a proposal which would eliminate a circulating lane within the roundabout. 

http://www.livingstondaily.com/story/news/local/community/green-oak-township/2016/06/10/lee-road-roundabout-redo-considered/85645684/

Here seems to be the trend when it comes to complex 2x2 and 2x3 multi-lane roundabouts in the United States:

1.   Agencies propose a complex multi-lane roundabout, citing safety studies that are heavily skewed towards single-lane and/or simplified 2x1 multi-lane roundabouts (ie. the 2000 Insurance Institute for Highway Safety study).
2.   The multi-lane roundabout is built and there is a big spike in total crashes.
3.   Agencies “tweak” the roundabout to combat the high crash rate, making minor pavement marking/signage changes.  While these tweaks can reduce the crash rate, they often leave a lot to be desired (ie. there is still too many crashes even after the tweaks).
4.   Agencies decide to remove a circulating lane inside the roundabout to simplify the design (converting 2x2 roundabouts to 2x1 or even single lane roundabouts).   Eliminating a circulating lane can often be done without affecting operation too much since the roundabout was originally designed for 2035 (or whatever) traffic volumes.  Simplifying the roundabout often solves the crash problem. 

Of the 2x2 and 2x3 roundabouts cited in this thread, many are seeing circulating lanes removes due to the high crash rates.  At what point do agencies question whether these complex roundabouts are acceptable in terms of safety?  Should these complex roundabouts be built in the first place if they are just going to be downsized within years of being constructed? 
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 13, 2016, 02:35:20 PM
The 10 Most Dangerous Roundabouts in Metro Detroit:

1. M-5/Martin Parkway at Pontiac Trail – Commerce Township Total crashes: 186

2. Van Dyke Ave. (M-53) at 18 1/2 Mile Road – Sterling Heights Total crashes: 124

3. State Street at Ellsworth Road – Ann Arbor/Pittsfield Township Total crashes: 114

4. Maple Road at Farmington Road – West Bloomfield Township Total crashes: 84

5. 14 Mile Road at Farmington Road – Farmington Hills/West Bloomfield Total crashes: 79

6. Maple Road at Drake Road – West Bloomfield Township Total crashes: 63

7. Lee Road at Whitmore Lake Road – Brighton/Green Oak Township Total crashes: 60

8. Martin Parkway at Oakley Park Road – Commerce Township Total crashes: 53

9. Hamlin Road at Livernois Road – Rochester Hills Total crashes: 41

10. Romeo Plank Road at 19 Mile Road – Clinton Township Total crashes: 37

http://womc.cbslocal.com/2016/05/11/the-10-most-dangerous-roundabouts-in-metro-detroit/
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 13, 2016, 02:49:03 PM
The roundabout at Van Dyke & 18 1/2 Mile in Metro Detroit was built over a decade ago.  In 2015 it had 124 crashes.  It may be an example of a roundabout that was overbuilt:

(http://www.atdetroit.net/forum/messages/107211/117735.jpg)
(http://www.atdetroit.net/forum/messages/107211/117734.jpg)

Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 25, 2016, 11:27:05 AM
New 2015 crash data released for SE Michigan.  The Ellsworth roundabout in Ann Arbor (which averaged 15.5 crashes before the roundabout) has averaged 140 crashes the first 2 years of operation.    If you dig deeper with the numbers, there was 2 injury crashes at the intersection from 2011-2012 (before data) and 9 injury crashes from 2014-2015 (after data). 

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Ells_zpspgdzs2in.png)
http://semcog.org/Data-and-Maps/High-Frequency-Crash-Locations

So to recap…
Average total crashes before roundabout = 15.5
Average total crashes after roundabout = 140
That’s a 803% increase  :wow:  in total crashes….

Average injury crashes before roundabout = 1
Average injury crashes after roundabout = 4.5
That’s a 350% increase  :crazy:  in injury crashes… 
Title: Re: Crash prone 'modern roundabouts'
Post by: 7/8 on July 25, 2016, 11:40:31 AM
New 2015 crash data released for SE Michigan.  The Ellsworth roundabout in Ann Arbor (which averaged 15.5 crashes before the roundabout) has averaged 140 crashes the first 2 years of operation.    If you dig deeper with the numbers, there was 2 injury crashes at the intersection from 2011-2012 (before data) and 9 injury crashes from 2014-2015 (after data). 

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Ells_zpspgdzs2in.png)
http://semcog.org/Data-and-Maps/High-Frequency-Crash-Locations

So to recap…
Average total crashes before roundabout = 15.5
Average total crashes after roundabout = 140
That’s a 803% increase  :wow:  in total crashes….

Average injury crashes before roundabout = 1
Average injury crashes after roundabout = 4.5
That’s a 350% increase  :crazy:  in injury crashes…

One problem I see with this roundabout is the lack of any obstruction in the centre. Even though it's counter-intuitive, it's better to block people from being able to see across the middle, since it's an unnecessary distraction. Putting some tall plants in the middle would force people to pay attention to cars on their left, like they should.

I still agree though that those crash statistics are still crazy, especially the increase in injury crashes!
https://www.google.ca/maps/@42.2292761,-83.7391719,3a,75y,54.44h,74.65t/data=!3m7!1e1!3m5!1srAaeg2wFciLs9vpdpmQH9A!2e0!6s%2F%2Fgeo2.ggpht.com%2Fcbk%3Fpanoid%3DrAaeg2wFciLs9vpdpmQH9A%26output%3Dthumbnail%26cb_client%3Dmaps_sv.tactile.gps%26thumb%3D2%26w%3D203%26h%3D100%26yaw%3D250.00459%26pitch%3D0!7i13312!8i6656 (https://www.google.ca/maps/@42.2292761,-83.7391719,3a,75y,54.44h,74.65t/data=!3m7!1e1!3m5!1srAaeg2wFciLs9vpdpmQH9A!2e0!6s%2F%2Fgeo2.ggpht.com%2Fcbk%3Fpanoid%3DrAaeg2wFciLs9vpdpmQH9A%26output%3Dthumbnail%26cb_client%3Dmaps_sv.tactile.gps%26thumb%3D2%26w%3D203%26h%3D100%26yaw%3D250.00459%26pitch%3D0!7i13312!8i6656)
(http://i.imgur.com/JyPhrx3.png)
Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on July 25, 2016, 11:46:33 AM
New 2015 crash data released for SE Michigan.  The Ellsworth roundabout in Ann Arbor (which averaged 15.5 crashes before the roundabout) has averaged 140 crashes the first 2 years of operation.    If you dig deeper with the numbers, there was 2 injury crashes at the intersection from 2011-2012 (before data) and 9 injury crashes from 2014-2015 (after data). 

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Ells_zpspgdzs2in.png)
http://semcog.org/Data-and-Maps/High-Frequency-Crash-Locations

So to recap…
Average total crashes before roundabout = 15.5
Average total crashes after roundabout = 140
That’s a 803% increase  :wow:  in total crashes….

Average injury crashes before roundabout = 1
Average injury crashes after roundabout = 4.5
That’s a 350% increase  :crazy:  in injury crashes…

One problem I see with this roundabout is the lack of any obstruction in the centre. Even though it's counter-intuitive, it's better to block people from being able to see across the middle, since it's an unnecessary distraction. Putting some tall plants in the middle would force people to pay attention to cars on their left, like they should.

I still agree though that those crash statistics are still crazy, especially the increase in injury crashes!
https://www.google.ca/maps/@42.2292761,-83.7391719,3a,75y,54.44h,74.65t/data=!3m7!1e1!3m5!1srAaeg2wFciLs9vpdpmQH9A!2e0!6s%2F%2Fgeo2.ggpht.com%2Fcbk%3Fpanoid%3DrAaeg2wFciLs9vpdpmQH9A%26output%3Dthumbnail%26cb_client%3Dmaps_sv.tactile.gps%26thumb%3D2%26w%3D203%26h%3D100%26yaw%3D250.00459%26pitch%3D0!7i13312!8i6656 (https://www.google.ca/maps/@42.2292761,-83.7391719,3a,75y,54.44h,74.65t/data=!3m7!1e1!3m5!1srAaeg2wFciLs9vpdpmQH9A!2e0!6s%2F%2Fgeo2.ggpht.com%2Fcbk%3Fpanoid%3DrAaeg2wFciLs9vpdpmQH9A%26output%3Dthumbnail%26cb_client%3Dmaps_sv.tactile.gps%26thumb%3D2%26w%3D203%26h%3D100%26yaw%3D250.00459%26pitch%3D0!7i13312!8i6656)
(http://i.imgur.com/JyPhrx3.png)

For a small roundabout like that, car across the circle is a potential conflict if making 270 turn. 
Title: Re: Crash prone 'modern roundabouts'
Post by: 7/8 on July 25, 2016, 11:57:02 AM
New 2015 crash data released for SE Michigan.  The Ellsworth roundabout in Ann Arbor (which averaged 15.5 crashes before the roundabout) has averaged 140 crashes the first 2 years of operation.    If you dig deeper with the numbers, there was 2 injury crashes at the intersection from 2011-2012 (before data) and 9 injury crashes from 2014-2015 (after data). 

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Ells_zpspgdzs2in.png)
http://semcog.org/Data-and-Maps/High-Frequency-Crash-Locations

So to recap…
Average total crashes before roundabout = 15.5
Average total crashes after roundabout = 140
That’s a 803% increase  :wow:  in total crashes….

Average injury crashes before roundabout = 1
Average injury crashes after roundabout = 4.5
That’s a 350% increase  :crazy:  in injury crashes…

One problem I see with this roundabout is the lack of any obstruction in the centre. Even though it's counter-intuitive, it's better to block people from being able to see across the middle, since it's an unnecessary distraction. Putting some tall plants in the middle would force people to pay attention to cars on their left, like they should.

I still agree though that those crash statistics are still crazy, especially the increase in injury crashes!
https://www.google.ca/maps/@42.2292761,-83.7391719,3a,75y,54.44h,74.65t/data=!3m7!1e1!3m5!1srAaeg2wFciLs9vpdpmQH9A!2e0!6s%2F%2Fgeo2.ggpht.com%2Fcbk%3Fpanoid%3DrAaeg2wFciLs9vpdpmQH9A%26output%3Dthumbnail%26cb_client%3Dmaps_sv.tactile.gps%26thumb%3D2%26w%3D203%26h%3D100%26yaw%3D250.00459%26pitch%3D0!7i13312!8i6656 (https://www.google.ca/maps/@42.2292761,-83.7391719,3a,75y,54.44h,74.65t/data=!3m7!1e1!3m5!1srAaeg2wFciLs9vpdpmQH9A!2e0!6s%2F%2Fgeo2.ggpht.com%2Fcbk%3Fpanoid%3DrAaeg2wFciLs9vpdpmQH9A%26output%3Dthumbnail%26cb_client%3Dmaps_sv.tactile.gps%26thumb%3D2%26w%3D203%26h%3D100%26yaw%3D250.00459%26pitch%3D0!7i13312!8i6656)
(http://i.imgur.com/JyPhrx3.png)

For a small roundabout like that, car across the circle is a potential conflict if making 270 turn. 

Here's a similar-sized (maybe even smaller?) roundabout in Kitchener, ON (Lancaster St and Bridge St) (https://www.google.ca/maps/@43.4823287,-80.4829546,3a,75y,107.05h,73.25t/data=!3m6!1e1!3m4!1snwrJ9k0G9fr6T6M0g8wUiQ!2e0!7i13312!8i6656) that has trees and bushes in the middle. Maybe this policy differs by region?
(http://i.imgur.com/Dwtc7dI.png)
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on July 25, 2016, 12:21:35 PM
Here's a similar-sized (maybe even smaller?) roundabout in Waterloo, ON (Lancaster St and Bridge St) (https://www.google.ca/maps/@43.4823287,-80.4829546,3a,75y,107.05h,73.25t/data=!3m6!1e1!3m4!1snwrJ9k0G9fr6T6M0g8wUiQ!2e0!7i13312!8i6656) that has trees and bushes in the middle. Maybe this policy differs by region?

http://i.imgur.com/Dwtc7dI.png

I'm not sure if it's official policy to decorate the center of the circle, but, it's highly recommended. Several guides that I've seen in the past recommend center decorations to prevent drivers from seeing more than just what's to the left of them.
Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on July 25, 2016, 12:37:27 PM

For a small roundabout like that, car across the circle is a potential conflict if making 270 turn. 

Here's asimilar-sized (maybe even smaller?) roundabout in Waterloo, ON (Lancaster St and Bridge St)[/url] that has trees and bushes in the middle. Maybe this policy differs by region?
Which tells nothing about safety of the design, any statistical data on this one?
With 30 meters diameter a car across has about 50 meters to travel before conflict. That is about 5 seconds at recommended speed, and 3 seconds since seeing it with decoration on the center. Is that enough to accelerate and clear the path? Most drivers don't really utilize full 0-60 acceleration rating  at each start... 
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 25, 2016, 01:47:06 PM
I'll bring this up here since it was mentioned in another thread.  Another complex crash prone roundabout is being simplified.  The Steptoe St. & Columbia Park roundabout in Tri-Cities, Washington is having a circulating lane removed inside the roundabout.  Yet another example of combating a high crash rate roundabout by removing a circulating lane:

http://goo.gl/kWNe0i
Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on July 25, 2016, 02:29:01 PM
I'll bring this up here since it was mentioned in another thread.  Another complex crash prone roundabout is being simplified.  The Steptoe St. & Columbia Park roundabout in Tri-Cities, Washington is having a circulating lane removed inside the roundabout.  Yet another example of combating a high crash rate roundabout by removing a circulating lane:

http://goo.gl/kWNe0i
Next step should be removal of central island and adding color coded signal light...
Title: Re: Crash prone 'modern roundabouts'
Post by: 7/8 on July 25, 2016, 03:02:40 PM

For a small roundabout like that, car across the circle is a potential conflict if making 270 turn. 

Here's a similar-sized (maybe even smaller?) roundabout in Kitchener, ON (Lancaster St and Bridge St) that has trees and bushes in the middle. Maybe this policy differs by region?

Which tells nothing about safety of the design, any statistical data on this one?
With 30 meters diameter a car across has about 50 meters to travel before conflict. That is about 5 seconds at recommended speed, and 3 seconds since seeing it with decoration on the center. Is that enough to accelerate and clear the path? Most drivers don't really utilize full 0-60 acceleration rating  at each start...

It's not in the top 100 most crash-prone intersections in the Region of Waterloo.
http://www.regionofwaterloo.ca/en/gettingAround/resources/2014-Collision-Ranking---By-Rank.pdf (http://www.regionofwaterloo.ca/en/gettingAround/resources/2014-Collision-Ranking---By-Rank.pdf)

I can't find any statistics for this roundabout though :/
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 25, 2016, 03:26:08 PM
It's not in the top 100 most crash-prone intersections in the Region of Waterloo.
http://www.regionofwaterloo.ca/en/gettingAround/resources/2014-Collision-Ranking---By-Rank.pdf (http://www.regionofwaterloo.ca/en/gettingAround/resources/2014-Collision-Ranking---By-Rank.pdf)

I can't find any statistics for this roundabout though :/

I don't see the Homer Watson Blvd and Block Road roundabout on that list.  Did they just leave out roundabouts in their analysis or is that intersection not part of the Waterloo region?

It's somewhat surprising they are going ahead with building a massive 3x2 roundabout at Ottawa Street & Homer Watson Blvd after all the issues with the Homer Watson Blvd & Block Road roundabout.  Based on your link, Ottawa Street & Homer Watson Blvd is the most crash prone intersection in the entire region.  Time will tell if the crash problem gets better or worse after the roundabout is completed. 

(http://i1309.photobucket.com/albums/s636/mithokey/db7262ee47b7a5bc63900ea74112-500x329_zpsapmftepa.jpeg)
http://www.waterlooregionconnected.com/printthread.php?tid=339&page=1
Title: Re: Crash prone 'modern roundabouts'
Post by: 7/8 on July 25, 2016, 03:52:22 PM
It's not in the top 100 most crash-prone intersections in the Region of Waterloo.
http://www.regionofwaterloo.ca/en/gettingAround/resources/2014-Collision-Ranking---By-Rank.pdf (http://www.regionofwaterloo.ca/en/gettingAround/resources/2014-Collision-Ranking---By-Rank.pdf)

I can't find any statistics for this roundabout though :/

I don't see the Homer Watson Blvd and Block Road roundabout on that list.  Did they just leave out roundabouts in their analysis or is that intersection not part of the Waterloo region?

I decided to read the full report this time, and I found this on page 35 (http://www.regionofwaterloo.ca/en/gettingAround/resources/2014_ANNUAL_COLLISION_REPORT.pdf)

(http://i.imgur.com/tAncAEP.png)

So, there are 13 roundabouts in the "Top 100" chart I posted earlier, but the other 7 roundabouts (as of 2014) were there for less than five years, so they were included in the table above. Unfortunately, there isn't much data there. I also still don't see the Bridgeport and Lancaster roundabout I mentioned earlier, maybe it's newer than I thought.

It's somewhat surprising they are going ahead with building a massive 3x2 roundabout at Ottawa Street & Homer Watson Blvd after all the issues with the Homer Watson Blvd & Block Road roundabout.  Based on your link, Ottawa Street & Homer Watson Blvd is the most crash prone intersection in the entire region.  Time will tell if the crash problem gets better or worse after the roundabout is completed. 

(http://i1309.photobucket.com/albums/s636/mithokey/db7262ee47b7a5bc63900ea74112-500x329_zpsapmftepa.jpeg)
http://www.waterlooregionconnected.com/printthread.php?tid=339&page=1

I know what you mean, and I'm sure this will be controversial. But the transportation departments in the Region and the Cities here seem to like roundabouts :-D. They're also putting in two roundabouts on Erb St west of the current roundabout with Ira Needles/Erbsville; they're building a new Costco and they believe it'll help with traffic flow.
Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on July 25, 2016, 04:02:30 PM
I know what you mean, and I'm sure this will be controversial. But the transportation departments in the Region and the Cities here seem to like roundabouts :-D. They're also putting in two roundabouts on Erb St west of the current roundabout with Ira Needles/Erbsville; they're building a new Costco and they believe it'll help with traffic flow.
Lets call it religious attitude. After all, it is for everyone's safety! And don't let stupid numbers to obscure the dogma  :poke:
Title: Re: Crash prone 'modern roundabouts'
Post by: lordsutch on July 25, 2016, 04:09:53 PM
Lets call it religious attitude. After all, it is for everyone's safety! And don't let stupid numbers to obscure the dogma  :poke:

Funny, that's what a lot of us would say about tradephoric's repeated goalpost-shifting in this thread.
Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on July 25, 2016, 05:33:38 PM
Lets call it religious attitude. After all, it is for everyone's safety! And don't let stupid numbers to obscure the dogma  :poke:

Funny, that's what a lot of us would say about tradephoric's repeated goalpost-shifting in this thread.
You see, I tried real hard - but looks like there is no solid justification for roundabouts published in English. There is some anecdotal evidence that those sometimes cause problems, and equally anecdotal evidence that is may sometimes work. But I didn't find any understanding of WHY and WHEN it goes one way or the other. But everyone is sure it is best thing since sliced bread.
There are some quite interesting works on lane capacity, for example. I didn't see anything of remotely similar quality about roundabouts... 
Title: Re: Crash prone 'modern roundabouts'
Post by: cjw2001 on July 25, 2016, 08:09:58 PM
Living in an area (near Carmel IN) with well over 100 roundabouts nearby, I can definitely state that the roundabouts provide a huge advantage for traffic flow.  It is so much better now for traveling the area without having to stop and wait at so many lights and stop signs.  Traffic used to back up significantly before the roundabouts were added.   Is it perfect?  No.  But it is far and away better than it was before the roundabouts were added.  Both my travel times and my gas mileage have noticeably improved.

I have no safety concerns driving the many roundabouts in the area.  A little bit of defensive driving (anticipate that there are other drivers on the road that don't know what they are doing) goes a long way toward avoiding any issues. 

The roundabouts are very popular with the local residents, and another 32 (http://www.carmel.in.gov/Modules/ShowDocument.aspx?documentID=7050) are going to be added within the next several years (http://www.indystar.com/story/news/local/hamilton-county/2016/01/06/carmel-outlines-bold-roundabout-plan/78258640/).  Can't wait for the further improvements in local traffic.



Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 26, 2016, 01:25:25 AM
I have no safety concerns driving the many roundabouts in the area.  A little bit of defensive driving (anticipate that there are other drivers on the road that don't know what they are doing) goes a long way toward avoiding any issues. 

Here is the citywide crash data for Carmel dating back to 2010.
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Carmelroundcrash_zpsdu8wf4uh.png)

There has been a 39% increase in total crashes (2442 crashes in 2015 / 1754 crashes in 2010) and a 56% increase in injury crashes (241 injury crashes in 2015 / 154 injury crashes in 2010).  The population of Carmel has increased 12% in the same time-frame (88,713 in 2015 / 79,191 in 2010).  Population data: http://www.carmel.in.gov/index.aspx?page=45

Ironically, both of Carmel’s fatal crashes in 2014 occurred at roundabouts.  Carmel still has its fair share of “dangerous” traffic signals; yet the “safe” roundabouts were the site of the fatal crashes.  We’ve all been told by the “experts” that roundabouts reduce fatal crashes by 90%.... perhaps they fabricated that safety statistic. 

http://fox59.com/2014/08/06/one-dead-in-carmel-accident-passenger-taken-to-hospital/
http://fox59.com/2014/09/26/person-dead-after-motorcycle-accident-in-carmel/
Title: Re: Crash prone 'modern roundabouts'
Post by: Rothman on July 26, 2016, 08:10:07 AM
Seems to me that there might have been a reporting change between 2013 and 2014. Quite the big data jump without an explanation of all the contributing factors.
Title: Re: Crash prone 'modern roundabouts'
Post by: 7/8 on July 28, 2016, 12:18:09 PM
Seems to me that there might have been a reporting change between 2013 and 2014. Quite the big data jump without an explanation of all the contributing factors.

For the Homer Watson/Block Line roundabout, the increase in crashes is likely due to the opening of the Block Line Rd bridge on Nov 22nd, 2013:
http://www.therecord.com/news-story/4230728-new-block-line-road-bridge-opening-friday-in-kitchener/ (http://www.therecord.com/news-story/4230728-new-block-line-road-bridge-opening-friday-in-kitchener/)

The bridge, location shown below, provides a useful E-W link between Homer Watson and Courtland Rd/Fairway Rd
(http://i.imgur.com/3fN8w9h.png)
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on July 28, 2016, 03:05:54 PM
http://wishtv.com/2015/10/08/roundabouts-may-confuse-but-stats-back-up-their-safety/
My favorite quote(s):
Quote
And even if you make a mistake, because speeds are so slow, most wrecks don’t involve serious injuries....[Carmel Mayor Jim Brainard] points out that because accidents and injuries are down in Carmel, insurance rates have dropped. He says the city doesn’t have a full “jaws of life” crew in its fire department anymore because they don’t have the high speed impacts that they used to have and don’t need them very often.

Total accidents and injury crashes have gone up in Carmel since that quote.  The number of injury crashes has risen 56% in Carmel over the past 6 years.  In addition the only two fatal crashes that occurred in Carmel in 2014 happened at roundabouts.  A lot of good it did not having a full “jaws of life” crew.  Let's all give Jim Brainard a hand for making his city so safe.  :clap:  :clap:  :clap:

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Carmelroundcrash_zpsdu8wf4uh.png)
Title: Re: Crash prone 'modern roundabouts'
Post by: epzik8 on July 30, 2016, 01:06:40 PM
Did anyone mention Maryland's Hampstead Bypass? I clinched Maryland Route 30 this month - I went straight from Reisterstown to Hanover, PA - and on the Hampstead Bypass, a car with a Pennsylvania plate whose driver was obviously headed to Hanover started to exit onto MD-482 east, then suddenly switched lanes right in front of me to stay on MD-30 north. It's a two-lane circle with the left lane in each direction at every circle intended for drivers staying on MD-30. Problem is, some drivers don't realize that and will then cut in front of you to avoid making a wrong turn onto 482 or Business 30 or whatever the cross street of that other circle is.

Honorable mention to the two-lane circle at U.S. 15 and MD-464 in Point of Rocks. Also to the pair of U.S. 15/U.S. 50 circles in Loudoun County, Virginia.
Title: Re: Crash prone 'modern roundabouts'
Post by: 7/8 on August 02, 2016, 07:12:34 PM
Manufacturers are designing bulky a-pillar in a quest to receive five star safety ratings.  Do bulky A-pillar designs reduce driver visibility and lead to drivers pulling out into the roundabout thinking it’s clear when it’s not?  The curves of a roundabout can make it easy for a vehicle to get lost in the a-pillar.

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/A-pillars_zpsrp1ucgda.jpg)
http://www.safespeed.org.uk/bike005.pdf

This is my biggest complaint about my current car, the Dodge Caliber. The pillars definitely reduce visibility. But I don't find them too bad with roundabouts; I find making left turns the worst, since pedestrians can easily "hide" behind them. I have to move head to see behind the pillars to make sure no one's there.
Title: Re: Crash prone 'modern roundabouts'
Post by: AlexandriaVA on August 05, 2016, 09:41:57 AM
Progress continutes. Carmel continues to build (http://fox59.com/2016/06/01/32-new-roundabouts-coming-to-carmel-timing-of-the-plan-outlined/)

Quote
"The vast majority of the money is going to improving our transportation system. Making it safer number one and then number two making it easier and quicker for people to get around," Mayor Jim Brainard said.

Quote
Mayor Brainard says the roundabouts make the city appealing.

"That's how we compete. That's how we attract business to the city of Carmel."
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on August 05, 2016, 09:59:53 AM
^The only two fatal crashes that occurred in Carmel in 2014 occurred at roundabouts.  What does Mayor Jim Brainard have to say about that?  Doesn't really fit into his PR campaign. 
Title: Re: Crash prone 'modern roundabouts'
Post by: cjw2001 on August 05, 2016, 10:06:55 AM
^The only two fatal crashes that occurred in Carmel in 2014 occurred at roundabouts.  What does Mayor Jim Brainard have to say about that?  Doesn't really fit into his PR campaign.

It's time to stop blaming the roundabout for drunk and / or speeding drivers.   There will be impaired drivers regardless of the road topology.   The fact that these intersections were roundabouts had little to do with the incidents in question.
Title: Re: Crash prone 'modern roundabouts'
Post by: AlexandriaVA on August 05, 2016, 10:32:22 AM
^The only two fatal crashes that occurred in Carmel in 2014 occurred at roundabouts.  What does Mayor Jim Brainard have to say about that?  Doesn't really fit into his PR campaign.

What about 2015 crash data? My guess is that it doesn't support your position so you decided to omit it.

Yes, fine people of the heartland, roundabouts are fine and will not eat you or your children. There is more to driving than stoplights or four-way stops.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on August 05, 2016, 10:56:26 AM
Alcohol was a factor in one of the fatal Carmel crashes in 2014. According to the NHTSA, there were 9,967 people killed in alcohol-impaired-driving crashes in 2014.  This accounted for 31 percent of all motor vehicle traffic fatalities in the United States that year.  The point is alcohol is a contributing factor to a LOT of fatal crashes; whether they happen at a roundabout, signalized intersection, or on the freeway.   

The national numbers on roundabouts suggest that they reduce fatal crashes by 90%.  These numbers obviously include fatal crashes involving alcohol.  If Carmel had 2 fatal crashes at their 100 roundabouts, you would expect to see roughly 20 fatal crashes throughout the rest of the city (Carmel does have its fair share of signalized intersections still.. someone just posted an article where 32 more roundabouts are planned, many of which will be replacing signalized intersections).

What about 2015 crash data? My guess is that it doesn't support your position so you decided to omit it.
Yes, fine people of the heartland, roundabouts are fine and will not eat you or your children. There is more to driving than stoplights or four-way stops.

You are suggesting that the 2014 Carmel crash data isn’t statistically significant by itself.  Just think of the hundreds of thousands of miles driven on Carmel roads in 2014.  Yet the only fatal crashes happened at roundabouts which are supposedly the safest places to be driving.  How is it that nobody was killed by some drunk at a signalized intersection (yes, they still exist in Carmel!)?  Or could it be, just maybe, that roundabouts don't reduce fatal crashes as much as they want us to believe?
Title: Re: Crash prone 'modern roundabouts'
Post by: AlexandriaVA on August 05, 2016, 11:11:04 AM
I thought it was because roundabouts are too difficult for Midwesterners to negotiate (as in you don't drive over them, or stop and make a left or right hand turn, etc etc).
Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on August 05, 2016, 11:34:08 AM

What about 2015 crash data? My guess is that it doesn't support your position so you decided to omit it.
Yes, fine people of the heartland, roundabouts are fine and will not eat you or your children. There is more to driving than stoplights or four-way stops.

You are suggesting that the 2014 Carmel crash data isn’t statistically significant by itself.  Just think of the hundreds of thousands of miles driven on Carmel roads in 2014.  Yet the only fatal crashes happened at roundabouts which are supposedly the safest places to be driving.  How is it that nobody was killed by some drunk at a signalized intersection (yes, they still exist in Carmel!)?  Or could it be, just maybe, that roundabouts don't reduce fatal crashes as much as they want us to believe?

Problem is that road statistics - especially accident statistics - and especially fatal accident data - is usually statistically insignificant to begin with. If you have a 10% accident reduction from 100 to 90, all you can say is that there is no statistically significant difference. No DOT would ignore the change, though.
  Some multiyear national trends may go better than error bars, but most of it is... well, if you don't have the data you like - you have to like the data you have.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on August 05, 2016, 11:42:01 AM
I thought it was because roundabouts are too difficult for Midwesterners to negotiate (as in you don't drive over them, or stop and make a left or right hand turn, etc etc).

You might be onto something.  The Midwest states are highlighted yellow as defined by the US Census Bureau.  The pink circles represent roundabouts that have 3 circulating lanes on at least one approach.  These are some of the most complex roundabouts that have been built in the United States.  As you can see, the majority of the complex roundabouts are located in the Midwest (specifically Wisconsin & Michigan).  So are the roundabouts too difficult for Midwestern drivers, or are they just being asked to navigate roundabouts that are more complex than the rest of the country? 

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/triplerbs_zpslnpx5k9e.png)

One interesting note… most of the regions in Wisconsin now have a moratorium on designing roundabouts with 3 circulating lanes.  Other state agencies should look closely at how triple lane roundabouts have evolved in Wisconsin before deciding to build a triple lane roundabout of their own.  In addition, several of the triple lane roundabouts in Michigan have since been downsized to only two-lanes with other roundabout downsizing planned (ie. Lee Road Roundabout).
Title: Re: Crash prone 'modern roundabouts'
Post by: AlexandriaVA on August 05, 2016, 11:46:29 AM
I thought Midwesterners like wide roads, so it would follow that the roundabouts should be wide as well.
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on August 05, 2016, 11:52:42 AM
I thought Midwesterners like wide roads, so it would follow that the roundabouts should be wide as well.

That's a pretty good point. Wisconsin in particular seems to have a large number of divided highways, ripe for three lane roundabouts. Same for Michigan.
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on August 05, 2016, 11:57:36 AM
Quote
The national numbers on roundabouts suggest that they reduce fatal crashes by 90%.  These numbers obviously include fatal crashes involving alcohol.  If Carmel had 2 fatal crashes at their 100 roundabouts, you would expect to see roughly 20 fatal crashes throughout the rest of the city...

No you wouldn't. Two issues with this:

You're looking at national numbers.  You're only looking at averages.  Not every single city, town, state, etc is going to see the same reduction.  In some states, there may be no reduction, in other states there could be a 100% reduction.  The *average* is a 90% reduction (at least what we're told).

And two, you can't take the number and say what the rest of the city/state should have had. If there were 0 DUI accidents at the roundabout (let's say that happened in 2015 because you ignored that data), then 90% would equal 0 DUI deaths in the rest of the city as well.  Is that true?  Probably not.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on August 05, 2016, 12:11:06 PM
And two, you can't take the number and say what the rest of the city/state should have had. If there were 0 DUI accidents at the roundabout (let's say that happened in 2015 because you ignored that data), then 90% would equal 0 DUI deaths in the rest of the city as well.  Is that true?  Probably not.

According to the Carmel, Indiana Police Department there was only 1 fatal crash in 2015 (and it did not occur at a roundabout).  I posted this data in chart form a few posts up, so I don’t see how I’m “ignoring” the data.  I gave you the source of the data and the number of fatalities that occurred in 2015 already (see Reply #552).  You were welcome to look up the data for yourself instead of relying on me.

There was another fatal roundabout crash in March of 2016:
http://www.indystar.com/story/news/crime/2016/03/18/driver-killed-carmel-roundabout-crash/81967984/

This was the first fatal crash to occur in Carmel in 2016.  So over a 27 month period, 3 of the 4 fatal crashes that occurred in Carmel happened at roundabouts.  Either the rest of Carmel’s street network is incredibly safe, or their roundabouts are much more dangerous than the roundabouts analyzed in the national studies.  The third option is you can just try to discredit the numbers and make an ineffective argument that 27 months isn’t statistically significant.
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on August 05, 2016, 12:18:09 PM
And two, you can't take the number and say what the rest of the city/state should have had. If there were 0 DUI accidents at the roundabout (let's say that happened in 2015 because you ignored that data), then 90% would equal 0 DUI deaths in the rest of the city as well.  Is that true?  Probably not.

According to the Carmel, Indiana Police Department there was only 1 fatal crash in 2015 (and it did not occur at a roundabout).  I posted this data in chart form a few posts up, so I don’t see how I’m “ignoring” the data.  I gave you the source of the data and the number of fatalities that occurred in 2015 already (see Reply #552).  You were welcome to look up the data for yourself instead of relying on me.

There was another fatal roundabout crash in March of 2016:
http://www.indystar.com/story/news/crime/2016/03/18/driver-killed-carmel-roundabout-crash/81967984/

This was the first fatal crash to occur in Carmel in 2016.  So over a 27 month period, 3 of the 4 fatal crashes that occurred in Carmel happened at roundabouts.  Either the rest of Carmel’s street network is incredibly safe, or their roundabouts are much more dangerous than the roundabouts analyzed in the national studies.  The third option is you can just try to discredit the numbers and make an ineffective argument that 27 months isn’t statistically significant.


The article stated he crashed into a concrete barrier in the middle of the roundabout.  As many other have pointed out in the past for similar accidents, that had nothing to do with a functionality failure of the roundabout. 

If anything, they need to figure out why drunks are flying thru roundabouts without turning.
Title: Re: Crash prone 'modern roundabouts'
Post by: 7/8 on August 05, 2016, 12:22:04 PM
I thought it was because roundabouts are too difficult for Midwesterners to negotiate (as in you don't drive over them, or stop and make a left or right hand turn, etc etc).

This reminds me that my grandad tried going "left" in a roundabout instead of going around the circle. The car in front of him had to stop, and the guy got out of his car and said "What are you doing?". My grandad said "I'm going over there!" :-D

He now has poor vision in his left eye, so you'll be glad to hear he no longer has his licence. :colorful:
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on August 05, 2016, 12:41:03 PM
The article stated he crashed into a concrete barrier in the middle of the roundabout.  As many other have pointed out in the past for similar accidents, that had nothing to do with a functionality failure of the roundabout. 

Use the same logic for someone who blows through a red light.  A driver blowing through a red light has nothing to do with the functionality failure of the traffic light.  But what is the point?  Ultimately, 3 out of 4 fatal crashes (75%) that have occurred in Carmel over a 27 month period happened at roundabouts.  This just doesn’t jive with what we have all been told by the experts.
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on August 05, 2016, 12:44:11 PM
I missed the story where the experts told us how many fatals to expect in a 27 month period in Carmel.  Can you post that link?
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on August 05, 2016, 02:02:15 PM
Are drink/driving collisions statistically significant? I mean, we want to prevent fatal collisions; roundabouts almost certainly have a better fatality record than intersections, simply because there's little in the way of right angles. But is there really anything we can do to meaningfully prevent said collisions? Short of further development in self-driving technology.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on August 05, 2016, 02:25:05 PM
It sounds like we want to ignore alcohol related fatalities in Carmel's roundabouts.  Fine, let's do that.  If you take out the roundabout fatalities that involved alcohol, you are still left with one fatal roundabout crash in 2014.  That means 50% of your fatalities in Carmel occurred at roundabouts over a 27 month period.  Carmel, the roundabout capital of the United States, where you are just as likely to die in a roundabout as anywhere else in the city. 
Title: Re: Crash prone 'modern roundabouts'
Post by: cjw2001 on August 05, 2016, 07:55:35 PM
It sounds like we want to ignore alcohol related fatalities in Carmel's roundabouts.  Fine, let's do that.  If you take out the roundabout fatalities that involved alcohol, you are still left with one fatal roundabout crash in 2014.  That means 50% of your fatalities in Carmel occurred at roundabouts over a 27 month period.  Carmel, the roundabout capital of the United States, where you are just as likely to die in a roundabout as anywhere else in the city.
I live locally to the area and fear not for my safety.

And to add an interesting data point, just one hour ago I was driving through the roundabout near my house on the way home.  Because of the reduced number of conflict points I was able to pay 100% attention to the idiot driver arriving at a high rate of speed from the road to my right (I had already entered the roundabout).   I was easily able to stop and avoid the idiot who blew through the yield sign.   You will have idiot drivers with all types of intersections, from personal experience I find it far easier to avoid the idiots with a roundabout than with other types of intersections where the idiots are approaching from all directions.

Also this was a Westfield roundabout, not a Carmel roundabout.   The Carmel roundabouts tend to have much better designed approach roads to force the approaching drivers to slow.   Never the less since I was oriented with a clear view of the approaching car it was very easy for me to take action to avoid the collision.


Title: Re: Crash prone 'modern roundabouts'
Post by: cjw2001 on August 05, 2016, 08:32:37 PM
For contrast, here is a story (http://fox59.com/2016/08/02/woman-badly-injured-after-crash-involving-ips-school-bus-witnesses-tell-police-bus-ran-stop-sign/) about a similar situation at a four way stop where the bus driver disregarded the stop sign and took out an SUV, sending the driver of the SUV to intensive care.  Likely would have been a far different result at a roundabout, where the bus driver would have had to slow somewhat and the SUV would have had a clear view of the approaching bus.
Title: Re: Crash prone 'modern roundabouts'
Post by: lordsutch on August 06, 2016, 01:54:37 AM
If you replace virtually all of the major intersections in a city with one of a particular type, virtually by definition nearly all of the deaths are going to be at that type of intersection, since people typically don't crash their cars in locations that aren't intersections (unless they fall asleep/have a heart attack at the wheel and run off the road).

Hence of course people are going to die in accidents in Carmel at roundabouts because there's almost no other type of intersection being used for major intersections in the city. If Carmel ripped them all out tomorrow and replaced them with all-way stops... all the deaths would now be at all-way stops (statistically there'd also be a lot more of them, although PDO crashes might go down).
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on August 06, 2016, 12:06:55 PM
Hence of course people are going to die in accidents in Carmel at roundabouts because there's almost no other type of intersection being used for major intersections in the city.

A lot of traffic signals and 4-way stops exist in Carmel, Indiana.  Here is a map that shows the current breakdown of traffic signals, roundabouts, and all-way stops:

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Carmel_zpsdca63r3q.png)
Green dots = roundabouts
Yellow dots = all-way stops
Red dots = traffic signals

As you can see, there is an even mix of roundabouts and non-roundabout intersections in the city.  The fact is there were 3 fatal crashes at Carmel’s roundabouts over a 27 month period (January 2014-March 2016).  Compare that to just one fatal crash at Carmel’s traffic signals and all-way stops during the same time period.  Carmel is the self-proclaimed roundabout capital of the country but it hasn’t had a good track record of preventing fatal crashes.  You have been better off driving through those “dangerous” red dots.
Title: Re: Crash prone 'modern roundabouts'
Post by: cjw2001 on August 06, 2016, 01:31:25 PM

I drive in this area every day, and I feel far safer in the roundabouts then at the traffic signals and four way stops.  Looking forward to the addition of 30 more. (http://www.indystar.com/story/news/local/hamilton-county/2016/01/06/carmel-outlines-bold-roundabout-plan/78258640/)

I find it amusing that someone from outside the area needs to tell me how I'm in so much danger.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on August 06, 2016, 02:57:38 PM
^ I find it amusing that you think your personal anecdotal evidence means anything.  It doesn’t change the facts.  National studies have suggested that roundabouts reduce fatal crashes by 90% yet Carmel has had triple the number of fatal crashes at their roundabouts than their signalized intersections over a 27 month period.  Go ahead and dispute that, but come back with some meaningful facts and not just anecdotal BS.
Title: Re: Crash prone 'modern roundabouts'
Post by: cjw2001 on August 06, 2016, 04:34:30 PM
^ I find it amusing that you think your personal anecdotal evidence means anything.  It doesn’t change the facts.  National studies have suggested that roundabouts reduce fatal crashes by 90% yet Carmel has had triple the number of fatal crashes at their roundabouts than their signalized intersections over a 27 month period.  Go ahead and dispute that, but come back with some meaningful facts and not just anecdotal BS.

I understand that you hate roundabouts, but that's no reason to go into name calling.  My personal experience is not BS.  I drive these roads every day.   Feel free to disagree, but don't call other people's posts BS.
Title: Re: Crash prone 'modern roundabouts'
Post by: silverback1065 on August 06, 2016, 07:04:10 PM
Hence of course people are going to die in accidents in Carmel at roundabouts because there's almost no other type of intersection being used for major intersections in the city.

A lot of traffic signals and 4-way stops exist in Carmel, Indiana.  Here is a map that shows the current breakdown of traffic signals, roundabouts, and all-way stops:

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Carmel_zpsdca63r3q.png)
Green dots = roundabouts
Yellow dots = all-way stops
Red dots = traffic signals

As you can see, there is an even mix of roundabouts and non-roundabout intersections in the city.  The fact is there were 3 fatal crashes at Carmel’s roundabouts over a 27 month period (January 2014-March 2016).  Compare that to just one fatal crash at Carmel’s traffic signals and all-way stops during the same time period.  Carmel is the self-proclaimed roundabout capital of the country but it hasn’t had a good track record of preventing fatal crashes.  You have been better off driving through those “dangerous” red dots.

In a city with over 100 roundabouts, having only 3 fatal crashes in over 2 years actually disproves your point completely.  I live in Carmel too, and it is much safer, and traffic moves much better.  Also why didn't you look at the stats when there were much more signals in the city?  How about when US 31 was completely signaled?  Not to mention the many accidents that occur at 96th and keystone, a signal.  The remaining signals in Carmel are all at not very busy intersections, so accidents wouldn't happen frequently.  Also, one of the 3 was a drunk driver who tried to drive straight through one.  2 of the red dots aren't even in carmel, they're in another community called Home Place that the county maintains.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on August 06, 2016, 09:04:19 PM
Not to mention the many accidents that occur at 96th and Keystone, a signal.

According to the Carmel Police Department’s 2014 Annual report the intersection of 96th & Keystone ranked in the top 20 highest crash locations with 38 total crashes.  But the roundabout at 116th & Keystone had even more with 68 total crashes.  Keep in mind all the through traffic on Keystone bypasses the 116th & Keystone roundabout so you would think it would experience much lower traffic volumes than the at-grade signalized intersection of 96th & Keystone.  The roundabout at 116th & Keystone had 78% more crashes than the traffic signal at 96th & Keystone yet you only want to point out the high number of crashes happening at the traffic signal.  Why are you ignoring the high crash roundabouts in your city?

You also mentioned that people were drinking in some of the fatal roundabout crashes that occurred over the past few years.  Ok.  What's your point?  The national studies don't omit fatal crashes just because someone was drunk.  According to the national studies, they cite roundabouts should lead to a significant reduction in fatal crashes.  We aren't seeing a reduction in fatalities in Carmel.  There are plenty of high volume signalized intersections remaining in Carmel, yet over the past few years the majority of fatal crashes in Carmel have happened at roundabouts.  It's not what you would expect in the roundabout capital of America.
Title: Re: Crash prone 'modern roundabouts'
Post by: silverback1065 on August 06, 2016, 09:06:41 PM
Not to mention the many accidents that occur at 96th and Keystone, a signal.

According to the Carmel Police Department’s 2014 Annual report the intersection of 96th & Keystone ranked in the top 20 highest crash locations with 38 total crashes.  But the roundabout at 116th & Keystone had even more with 68 total crashes.  Keep in mind all the through traffic on Keystone bypasses the 116th & Keystone roundabout so you would think it would experience much lower traffic volumes than the at-grade signalized intersection of 96th & Keystone.  The roundabout at 116th & Keystone had 78% more crashes than the traffic signal at 96th & Keystone yet you only want to point out the high number of crashes happening at the traffic signal.  Why are you ignoring the high crash roundabouts in your city?

You also mentioned that people were drinking in some of the fatal roundabout crashes that occurred over the past few years.  Ok.  What's your point?  The national studies don't omit fatal crashes just because someone was drunk.  According to the national studies, they cite roundabouts should lead to a significant reduction in fatal crashes.  We aren't seeing a reduction in fatalities in Carmel.  There are plenty of high volume signalized intersections remaining in Carmel, yet over the past few years the majority of fatal crashes in Carmel have happened at roundabouts.  It's not what you would expect in the roundabout capital of America.
It's exactly what you would expect in a city where the primary feature is a roundabout. What's your point?
You are basically trying to say roundabouts should have no crashes. Signals have many safety issues that are well documented. You also don't even account traffic volume in your analysis.
You could put the same analysis with Indianapolis comparing it's many signals to the small amount of roundabouts and come to the opposite conclusion.
I'd also like to see before and after analysis to see if the signal had more or less crashes than the roundabout.
Title: Re: Crash prone 'modern roundabouts'
Post by: silverback1065 on August 06, 2016, 09:30:15 PM
Honestly, Jim Brainard has kind of lost his mind when it comes to roundabouts, there are some in the city that honestly don't need to be there at all, or the signal was fine. I feel he's more concerned about traffic flow than accidents.


Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on August 06, 2016, 11:03:23 PM
In a city with over 100 roundabouts, having only 3 fatal crashes in over 2 years actually disproves your point completely.  I live in Carmel too, and it is much safer, and traffic moves much better.  Also why didn't you look at the stats when there were much more signals in the city?  How about when US 31 was completely signaled?  Not to mention the many accidents that occur at 96th and keystone, a signal.  The remaining signals in Carmel are all at not very busy intersections, so accidents wouldn't happen frequently.  Also, one of the 3 was a drunk driver who tried to drive straight through one.  2 of the red dots aren't even in carmel, they're in another community called Home Place that the county maintains.

Honestly speaking, feeling safer has very little to do with actual safety. And they don't care about your beliefs in intensive care unit.

You are basically trying to say roundabouts should have no crashes. Signals have many safety issues that are well documented. You also don't even account traffic volume in your analysis.
Traffic lights problems may be well documented - but main problem of roundabouts is lack of understanding. Unfortunately, my strong impression is that US has few qualified traffic engineers left.
There were some people in Ireland trying to perform in-depth analysis of roundabouts. If you look at their publications, it is pretty clear where roundabouts actually belong and where they don't. But those publications seem way beyond comprehension level of those in charge.
Title: Re: Crash prone 'modern roundabouts'
Post by: silverback1065 on August 06, 2016, 11:31:31 PM
One of the bigger problems is that a lot of times, they're just a rubber stamp for what the mayor wants. And this is definitely true of Carmel. Even if they disagree with the mayor, they'll get overruled.

Nexus 6P

Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on August 07, 2016, 10:06:59 AM
Unfortunately, my strong impression is that US has few qualified traffic engineers left.

This statement would be a candidate for the most grossly inaccurate statement of the year.

Unless the roads you're driving on are collapsing on a daily basis, a traffic engineer created or signed off on that design that's keeping you safe.

If people can't negotiate roundabouts, that doesn't mean a traffic engineer messed up. It means the motorist messed up.

Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on August 07, 2016, 10:14:18 AM
Unfortunately, my strong impression is that US has few qualified traffic engineers left.

This statement would be a candidate for the most grossly inaccurate statement of the year.

Unless the roads you're driving on are collapsing on a daily basis, a traffic engineer created or signed off on that design that's keeping you safe.

If people can't negotiate roundabouts, that doesn't mean a traffic engineer messed up. It means the motorist messed up.

There is structural engineering, and there is traffic engineering. I sure hope that the guy who designed the concrete of the bridge is not the one who designed stripping on it - you know, I cannot afford a helicopter...
Alternatively, if it is indeed same guy, I would pray that he knows structural things. As for stripping.. Well, bridge wouldn't collapse because of stripping....
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on August 07, 2016, 10:16:25 AM
Unfortunately, my strong impression is that US has few qualified traffic engineers left.

This statement would be a candidate for the most grossly inaccurate statement of the year.

Unless the roads you're driving on are collapsing on a daily basis, a traffic engineer created or signed off on that design that's keeping you safe.

If people can't negotiate roundabouts, that doesn't mean a traffic engineer messed up. It means the motorist messed up.

There is structural engineering, and there is traffic engineering. I sure hope that the guy who designed the concrete of the bridge is not the one who designed stripping on it - you know, I cannot afford a helicopter...
Alternatively, if it is indeed same guy, I would pray that he knows structural things. As for stripping.. Well, bridge wouldn't collapse because of stripping....

Put the stripping too close to the outer edge of the bridge, where the bridge height may fall under 13' 6", and have a truck come along...
Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on August 07, 2016, 10:26:22 AM
Unfortunately, my strong impression is that US has few qualified traffic engineers left.

This statement would be a candidate for the most grossly inaccurate statement of the year.

Unless the roads you're driving on are collapsing on a daily basis, a traffic engineer created or signed off on that design that's keeping you safe.

If people can't negotiate roundabouts, that doesn't mean a traffic engineer messed up. It means the motorist messed up.

There is structural engineering, and there is traffic engineering. I sure hope that the guy who designed the concrete of the bridge is not the one who designed stripping on it - you know, I cannot afford a helicopter...
Alternatively, if it is indeed same guy, I would pray that he knows structural things. As for stripping.. Well, bridge wouldn't collapse because of stripping....

Put the stripping too close to the outer edge of the bridge, where the bridge height may fall under 13' 6", and have a truck come along...

Oh, OK.. Looks like I have to start saving for a helicopter...
Title: Re: Crash prone 'modern roundabouts'
Post by: silverback1065 on August 07, 2016, 12:06:32 PM
Striping and signage isn't the problem, driver fuck ups are, hard to negotiate a roundabout when your texting or pokemon going.  I still see people trying to make a left turn in a roundabout (the wrong way) there is obvious signage, striping, fuck the damn median forces you to go right.  I think another problem is people incorrectly assuming where people in the roundabout are going and causing crashes, since you cannot signal in a roundabout, you have to wait.
Title: Re: Crash prone 'modern roundabouts'
Post by: silverback1065 on August 07, 2016, 12:07:33 PM
Unfortunately, my strong impression is that US has few qualified traffic engineers left.

This statement would be a candidate for the most grossly inaccurate statement of the year.

Unless the roads you're driving on are collapsing on a daily basis, a traffic engineer created or signed off on that design that's keeping you safe.

If people can't negotiate roundabouts, that doesn't mean a traffic engineer messed up. It means the motorist messed up.

I agree that statement is bullshit
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on August 07, 2016, 12:38:42 PM
Here on the west coast, some of the engineering schools are exceptionally difficult to get into, due to the recent influx of students from China. These students are exceptionally good at math, and present stiff competition when applying for an engineering program.

My point being, only the very best of the best are getting into engineering programs (at least out here).
Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on August 07, 2016, 12:49:22 PM
Here on the west coast, some of the engineering schools are exceptionally difficult to get into, due to the recent influx of students from China. These students are exceptionally good at math, and present stiff competition when applying for an engineering program.

My point being, only the very best of the best are getting into engineering programs (at least out here).
Best of best are applying for medical and MBA programs. That's where money is. 
And in any case, most roads we have today were designed 15 years ago and build 10 years ago by those who graduated  20-25 years ago and now think about retirement.  That is optimistic  scenario - average bridge age in US is 50 years, you know..
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on August 08, 2016, 11:36:12 AM
Yet another 3x2 crash prone roundabout has been downsized to a 2x2 roundabout.  The roundabout at 14 Mile & Farmington in West Bloomfield, Michigan was recently restriped to only include two circulating lanes through the roundabout.  According to MDOT, there were 36.43 average crashes before the roundabout was built and 67.33 average crashes after the roundabout (http://www.michigan.gov/documents/mdot/MDOT_Research_Report_RC1566_379286_7.pdf).  This follows the downsizing of other 3x2 roundabouts in the area including the one at Maple & Farmington and Maple & Drake. 

The remaining 3x2 roundabout in the area is the one at Pontiac Trail & M-5 (which was originally constructed in 2011).  The Pontiac Trail & M-5 roundabout was the highest crash prone intersection in the entire state of Michigan for 2015 with 186 total crashes (the intersection of 12 Mile & Telegraph ranked second with 132 crashes).
http://www.freep.com/story/news/local/michigan/oakland/2016/06/05/oakland-county-most-dangerous-intersection-state/85305668/
Title: Re: Crash prone 'modern roundabouts'
Post by: JCinSummerfield on August 08, 2016, 01:46:32 PM
Here in Toledo, OH, the intersection of Cherry, Berdan & Detroit Streets has been a roundabout for several months now.  Accidents occur daily.  What nobody has figured out is that the signage and the pavement striping don't match - at least entering from Cherry St.  I've also seen people make the wrong move for the lane they are in, so it's a combination of engineering issues and driver issues.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on August 08, 2016, 02:28:23 PM
Here in Toledo, OH, the intersection of Cherry, Berdan & Detroit Streets has been a roundabout for several months now.  Accidents occur daily.  What nobody has figured out is that the signage and the pavement striping don't match - at least entering from Cherry St.  I've also seen people make the wrong move for the lane they are in, so it's a combination of engineering issues and driver issues.

Wow, you’re not kidding.  A lot of people traveling on Cherry Street would assume that continuing on Detroit Avenue is the “straight” movement while continuing onto Berdan Avenue would be the "turn" movement.  The pavement markings direct vehicles who entered the roundabout from the left lane to continue straight onto Detroit Avenue (and conversely, right lane traffic who enters the roundabout have to cross a solid white line to continue onto Berdan Ave).  I definitely could see myself getting confused driving this roundabout and i should know better.  I’m sure in the next few posts someone with a PHD in roundabout design will explain why the pavement markings and signage is correct, without considering how confusing it is to the average Joe.

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Toledocon_zpsdfrdsnw7.png)

The most likely scenario is in a few years time, they will make the right most lane a right turn only lane and convert it to a 2x1 roundabout to limit confusion (and to alleviate the high crash rate).
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on August 08, 2016, 04:41:54 PM
Here in Toledo, OH, the intersection of Cherry, Berdan & Detroit Streets has been a roundabout for several months now.  Accidents occur daily.  What nobody has figured out is that the signage and the pavement striping don't match - at least entering from Cherry St.  I've also seen people make the wrong move for the lane they are in, so it's a combination of engineering issues and driver issues.

Wow, you’re not kidding.  A lot of people traveling on Cherry Street would assume that continuing on Detroit Avenue is the “straight” movement while continuing onto Berdan Avenue would be the "turn" movement.  The pavement markings direct vehicles who entered the roundabout from the left lane to continue straight onto Detroit Avenue (and conversely, right lane traffic who enters the roundabout have to cross a solid white line to continue onto Berdan Ave).  I definitely could see myself getting confused driving this roundabout and i should know better.  I’m sure in the next few posts someone with a PHD in roundabout design will explain why the pavement markings and signage is correct, without considering how confusing it is to the average Joe.

http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Toledocon_zpsdfrdsnw7.png

This is why, under certain circumstances, I prefer no lane markings to confusing lane markings. If this roundabout didn't have any lane markings, traffic may be able to better interpret the through movement, but the way it's setup, through traffic has no chance: the movement becomes less of a straight-on movement, and more of a "merge then slight left", all because of the solid lane line.
Title: Re: Crash prone 'modern roundabouts'
Post by: 7/8 on August 08, 2016, 06:48:34 PM
Here in Toledo, OH, the intersection of Cherry, Berdan & Detroit Streets has been a roundabout for several months now.  Accidents occur daily.  What nobody has figured out is that the signage and the pavement striping don't match - at least entering from Cherry St.  I've also seen people make the wrong move for the lane they are in, so it's a combination of engineering issues and driver issues.

Wow, you’re not kidding.  A lot of people traveling on Cherry Street would assume that continuing on Detroit Avenue is the “straight” movement while continuing onto Berdan Avenue would be the "turn" movement.  The pavement markings direct vehicles who entered the roundabout from the left lane to continue straight onto Detroit Avenue (and conversely, right lane traffic who enters the roundabout have to cross a solid white line to continue onto Berdan Ave).  I definitely could see myself getting confused driving this roundabout and i should know better.  I’m sure in the next few posts someone with a PHD in roundabout design will explain why the pavement markings and signage is correct, without considering how confusing it is to the average Joe.

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/Toledocon_zpsdfrdsnw7.png)

I'm struggling to see how someone could defend this, it just seems wrong to me! :pan:

The most likely scenario is in a few years time, they will make the right most lane a right turn only lane and convert it to a 2x1 roundabout to limit confusion (and to alleviate the high crash rate).

This would be the easiest way to solve the problem, and at least you wouldn't have to change that stripe in the roundabout. :-D

Ideally, they should have had Cherry St bend to the west before the roundabout to prevent the confusion about Detroit St being a "right turn". But maybe they didn't have the ROW?
Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on August 09, 2016, 08:21:33 AM
I'm struggling to see how someone could defend this, it just seems wrong to me! :pan:
Pretty obvious, if you zoom out, you can clearly see which road goes through and which is turning.
And if average Joe is so stupid that he cannot see the big picture while driving through, that is not engineer's problem!

However, honestly speaking, pre-roundabout layout which still shows on web maps, is not much better. I have hard time thinking of a good layout - really no straightforward solution, and local traffic pattern has to be taken into account. And overall area looks... messy. With lots of homes, lots of commute, and lots of NIMBYs.... 
Title: Re: Crash prone 'modern roundabouts'
Post by: 7/8 on August 09, 2016, 08:45:33 AM
I'm struggling to see how someone could defend this, it just seems wrong to me! :pan:
Pretty obvious, if you zoom out, you can clearly see which road goes through and which is turning.
And if average Joe is so stupid that he cannot see the big picture while driving through, that is not engineer's problem!.

I probably could have been more clear here, but I was referring to the solid white line in the roundabout. The sign on Cherry St says you can go straight or right, but the solid white line (next to the red car in the satellite image) suggests that you can only go right, since going straight would require you to cross a solid white line.

As to the problem of drivers thinking Cherry St to N Detroit Ave is "straight" instead of a right-turn, I can see both sides of the coin. And though I understand your point, the fact is (to a certain extent) we need to design roads for stupid drivers because many drivers are stupid. Especially when it comes to roundabouts (in North America anyway), as all the crash statistics in this thread prove.
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on August 09, 2016, 08:53:32 AM
I'm struggling to see how someone could defend this, it just seems wrong to me! :pan:
Pretty obvious, if you zoom out, you can clearly see which road goes through and which is turning.
And if average Joe is so stupid that he cannot see the big picture while driving through, that is not engineer's problem!.

I probably could have been more clear here, but I was referring to the solid white line in the roundabout. The sign on Cherry St says you can go straight or right, but the solid white line (next to the red car in the satellite image) suggests that you can only go right, since going straight would require you to cross a solid white line.

If anyone commenting missed that, then they need to turn in their roadgeek license!  :spin: 
Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on August 09, 2016, 10:31:18 AM
I'm struggling to see how someone could defend this, it just seems wrong to me! :pan:
Pretty obvious, if you zoom out, you can clearly see which road goes through and which is turning.
And if average Joe is so stupid that he cannot see the big picture while driving through, that is not engineer's problem!.

I probably could have been more clear here, but I was referring to the solid white line in the roundabout. The sign on Cherry St says you can go straight or right, but the solid white line (next to the red car in the satellite image) suggests that you can only go right, since going straight would require you to cross a solid white line.

As to the problem of drivers thinking Cherry St to N Detroit Ave is "straight" instead of a right-turn, I can see both sides of the coin. And though I understand your point, the fact is (to a certain extent) we need to design roads for stupid drivers because many drivers are stupid. Especially when it comes to roundabouts (in North America anyway), as all the crash statistics in this thread prove.

I would interpret "straight" on that lane as "Straight to N Detroit", and "right" - as "right to Emmet st. off N Detroit".
If they had that in mind .. but probably not - sign at the roundabout entry shows that right lane goes to Detroit and Berdan, and left.... to Berdan and Detroit as well.

Talk about levels of confusion!
Title: Re: Crash prone 'modern roundabouts'
Post by: 7/8 on August 09, 2016, 10:54:26 AM
I'm struggling to see how someone could defend this, it just seems wrong to me! :pan:
Pretty obvious, if you zoom out, you can clearly see which road goes through and which is turning.
And if average Joe is so stupid that he cannot see the big picture while driving through, that is not engineer's problem!.

I probably could have been more clear here, but I was referring to the solid white line in the roundabout. The sign on Cherry St says you can go straight or right, but the solid white line (next to the red car in the satellite image) suggests that you can only go right, since going straight would require you to cross a solid white line.

As to the problem of drivers thinking Cherry St to N Detroit Ave is "straight" instead of a right-turn, I can see both sides of the coin. And though I understand your point, the fact is (to a certain extent) we need to design roads for stupid drivers because many drivers are stupid. Especially when it comes to roundabouts (in North America anyway), as all the crash statistics in this thread prove.

I would interpret "straight" on that lane as "Straight to N Detroit", and "right" - as "right to Emmet st. off N Detroit".
If they had that in mind .. but probably not - sign at the roundabout entry shows that right lane goes to Detroit and Berdan, and left.... to Berdan and Detroit as well.

Talk about levels of confusion!

Interesting, Google Maps doesn't show Emmet St connecting to N Detroit Ave, but this GSV from Sept 2015 suggests it does. The bolded sentence above is another good point of potential motorist confusion!

(http://i.imgur.com/MVmEU4c.png)
(http://i.imgur.com/XoLP2Dp.png)

Also, Google Maps shows (a second Cherry St?) connecting to the roundabout at W Manhattan Blvd going the wrong way!

(http://i.imgur.com/jsebqb9.png)

But GSV confirms this is an error and that this street doesn't connect to the roundabout.

(http://i.imgur.com/Pm3vklV.png)

The outdated satellite imagery doesn't help with all this confusion :colorful:
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on August 09, 2016, 10:58:35 AM

(http://i.imgur.com/Pm3vklV.png)


Uh....................
Title: Re: Crash prone 'modern roundabouts'
Post by: 7/8 on August 09, 2016, 11:26:49 AM

(http://i.imgur.com/Pm3vklV.png)


Uh....................

I'm not sure why you're confused. I posted the GSV image to show that the street in the background with the houses on it doesn't connect to the roundabout (there's grass between the two), whereas Google Maps seems to show them overlapping.
Title: Re: Crash prone 'modern roundabouts'
Post by: kphoger on August 09, 2016, 12:22:49 PM

(http://i.imgur.com/Pm3vklV.png)


Uh....................

I'm not sure why you're confused. I posted the GSV image to show that the street in the background with the houses on it doesn't connect to the roundabout (there's grass between the two), whereas Google Maps seems to show them overlapping.

I'm confused by cars driving in opposite directions on the same roundabout.
Title: Re: Crash prone 'modern roundabouts'
Post by: 7/8 on August 09, 2016, 12:25:28 PM

(http://i.imgur.com/Pm3vklV.png)


Uh....................

I'm not sure why you're confused. I posted the GSV image to show that the street in the background with the houses on it doesn't connect to the roundabout (there's grass between the two), whereas Google Maps seems to show them overlapping.

I'm confused by cars driving in opposite directions on the same roundabout.

Holy crap, I guess that's what he was referring to! :-D I should post that in the Google Street View thread

UPDATE: Here's my post with more views of the wrong way driver: http://www.aaroads.com/forum/index.php?topic=2648.msg2165328#msg2165328 (http://www.aaroads.com/forum/index.php?topic=2648.msg2165328#msg2165328)
Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on August 09, 2016, 12:26:46 PM

(http://i.imgur.com/Pm3vklV.png)


Uh....................

I'm not sure why you're confused. I posted the GSV image to show that the street in the background with the houses on it doesn't connect to the roundabout (there's grass between the two), whereas Google Maps seems to show them overlapping.

FOr me new alignment shows up when I untilt the image, old one with tilted image.

And Emmet street is clearly connected to Detroit just off roundabout, maybe 70 feet down the street.
https://www.google.com/maps/place/Toledo,+OH/@41.6863319,-83.5568115,19z/data=!3m1!1e3!4m2!3m1!1s0x883b872dfc1e4e79:0x7c3cc89f453ac345
https://www.google.com/maps/place/Toledo,+OH/@41.6862413,-83.5560435,3a,66.8y,90t/data=!3m4!1e1!3m2!1sohHAkXupMp-umJA_rgki5w!2e0!4m2!3m1!1s0x883b872dfc1e4e79:0x7c3cc89f453ac345
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on August 09, 2016, 01:26:19 PM

(http://i.imgur.com/Pm3vklV.png)


Uh....................

I'm not sure why you're confused. I posted the GSV image to show that the street in the background with the houses on it doesn't connect to the roundabout (there's grass between the two), whereas Google Maps seems to show them overlapping.

I'm confused by cars driving in opposite directions on the same roundabout.

Holy crap, I guess that's what he was referring to! :-D

That's exactly what I was referring to!!!!
Title: Re: Crash prone 'modern roundabouts'
Post by: jakeroot on August 09, 2016, 04:07:17 PM
What if you just removed the confusing markings? Install overhead signage that clearly shows the straight movement as being a "slight right then left". Or even change the arrows so that they point slightly left instead of straight.

I don't think you need to remove any lanes to fix the problem here. Although apparently we need more right-facing chevrons, because there's evidently people out there that still don't know which way to go around a roundabout....

(http://i.imgur.com/NdJeFct.png)
Title: Re: Crash prone 'modern roundabouts'
Post by: kalvado on August 09, 2016, 04:31:47 PM
What if you just removed the confusing markings? Install overhead signage that clearly shows the straight movement as being a "slight right then left". Or even change the arrows so that they point slightly left instead of straight.

I don't think you need to remove any lanes to fix the problem here. Although apparently we need more right-facing chevrons, because there's evidently people out there that still don't know which way to go around a roundabout....

Actually I was staring at the map trying to visualize traffic patterns.. Looks like there is a massive amount of rebuild going on in the area - I-75 bridge, those two roundabouts, C/D road to I-75. And area looks mostly residential, with lots of homes. Commuter traffic struggling during roadwork in crazy traffic pattern?
Google also shows another roundabout in progress about 1/4 mile west.. Looks like a major realignment of everything..
Title: Re: Crash prone 'modern roundabouts'
Post by: lordsutch on August 09, 2016, 04:42:47 PM
What if you just removed the confusing markings? Install overhead signage that clearly shows the straight movement as being a "slight right then left". Or even change the arrows so that they point slightly left instead of straight.

Most non-signalized 2x2 or 2x1 roundabouts in the UK don't have lane markings, for what it's worth.

Quote
I don't think you need to remove any lanes to fix the problem here. Although apparently we need more right-facing chevrons, because there's evidently people out there that still don't know which way to go around a roundabout....

On the other hand, chevrons (along with a mandatory turn one-way arrow) are probably more, not less, emphasized in the UK (except mini-roundabouts, for obvious reasons) than most US installations. Using a W1-6 on top of the chevrons would probably get the point across better, but for some reason MUTCD doesn't specify that.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on August 09, 2016, 05:40:51 PM
It would be interesting to see if this design would work or if the traffic volumes turning onto Berdan Ave are too high (requiring the dual circulating lanes).....

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/rbredesign_zpsbffmrhx1.png)

Title: Re: Crash prone 'modern roundabouts'
Post by: johndoe on August 09, 2016, 06:55:39 PM
I have a cheaper fix =)
(http://i63.tinypic.com/sdimue.jpg)

What if you just removed the confusing markings?
Do you find the circulating roadway markings/arrows more confusing than the approach fishhooks?  Usually the normal arrows in the circulating roadway align nicely with the exit (unless the angle between legs is big like this), but it makes a lot of sense to me that "through"="exiting roundabout" and "left"="circulating roundabout" but there's a decent chance I've looked at these things too long =)  I guess I've never understood the desire to remove circulating markings. 

IMO if anything is confusing it's the fishhooks.  We've had lots of debate in our office about their effectiveness!  Some people think the angle between the arrows is most important, while others think it's more about demonstrating which lane can exit at which departure (for instance in the left lane you cannot use the FIRST exit but you can use the second and third).  Just be glad this is only four-legged; things get really weird with a fifth leg!
Title: Re: Crash prone 'modern roundabouts'
Post by: cjw2001 on August 10, 2016, 09:44:00 AM
I'm struggling to see how someone could defend this, it just seems wrong to me! :pan:
Pretty obvious, if you zoom out, you can clearly see which road goes through and which is turning.
And if average Joe is so stupid that he cannot see the big picture while driving through, that is not engineer's problem!.

I probably could have been more clear here, but I was referring to the solid white line in the roundabout. The sign on Cherry St says you can go straight or right, but the solid white line (next to the red car in the satellite image) suggests that you can only go right, since going straight would require you to cross a solid white line.

As to the problem of drivers thinking Cherry St to N Detroit Ave is "straight" instead of a right-turn, I can see both sides of the coin. And though I understand your point, the fact is (to a certain extent) we need to design roads for stupid drivers because many drivers are stupid. Especially when it comes to roundabouts (in North America anyway), as all the crash statistics in this thread prove.

I would interpret "straight" on that lane as "Straight to N Detroit", and "right" - as "right to Emmet st. off N Detroit".
If they had that in mind .. but probably not - sign at the roundabout entry shows that right lane goes to Detroit and Berdan, and left.... to Berdan and Detroit as well.

Talk about levels of confusion!

Interesting, Google Maps doesn't show Emmet St connecting to N Detroit Ave, but this GSV from Sept 2015 suggests it does. The bolded sentence above is another good point of potential motorist confusion!

(http://i.imgur.com/MVmEU4c.png)
(http://i.imgur.com/XoLP2Dp.png)

Also, Google Maps shows (a second Cherry St?) connecting to the roundabout at W Manhattan Blvd going the wrong way!

(http://i.imgur.com/jsebqb9.png)

But GSV confirms this is an error and that this street doesn't connect to the roundabout.

(http://i.imgur.com/Pm3vklV.png)

The outdated satellite imagery doesn't help with all this confusion :colorful:

I've corrected the geometry on the second cherry street to the left in mapmaker (it wasn't connected to the roundabout, just drawn too far to the right).   I also removed the building outline that was sitting on top of the roundabout and cleaned up some of the other geometry.   Also connected Emmet Street and split the lanes on North Detroit north of the roundabout.   Will require google moderation for the final touches to set the new lanes to the right highway priority.

Give it 24 hours for everything to show up on maps.
Title: Re: Crash prone 'modern roundabouts'
Post by: jeffandnicole on August 10, 2016, 10:24:38 AM
What if you just removed the confusing markings? Install overhead signage that clearly shows the straight movement as being a "slight right then left". Or even change the arrows so that they point slightly left instead of straight.

Most non-signalized 2x2 or 2x1 roundabouts in the UK don't have lane markings, for what it's worth.

Most NJ traffic circles don't have lane markings either.  People do have a tendency to creep into other lanes when they're not supposed to.  Plenty of horn honking.  And yet, they don't seem to have the issues many others report at these fully parked roundabouts.
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on August 10, 2016, 10:52:10 AM
Here is a good streetview compilation of the problem.  In the very first picture there is a sign that directs drivers what lane to be in depending if they want to go on Detroit Ave or Berdan Ave.  Track the white Lincoln Towncar through the roundabout.  The white Lincoln correctly follows the signage and continues onto Berdan Ave (although they have to cross a solid white line inside the roundabout to get there).  Now track the red Camero who was at one point directly beside the white Lincoln.  Both the red Camero and the vehicle behind them incorrectly continues onto Detroit Avenue.  This is your problem.. drivers in the left lane are exiting onto Detroit Ave and they shouldn't be. 
 
(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/trackcab2_zpsxn2rhqdo.png)

(http://i478.photobucket.com/albums/rr144/tradephoric/Transportation%20Pictures/Roundabouts/trackredcamero2_zpsbbjjvn32.png)
Title: Re: Crash prone 'modern roundabouts'
Post by: tradephoric on August 10, 2016, 11:33:40 AM