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Crash prone 'modern roundabouts'

Started by tradephoric, May 18, 2015, 02:51:37 PM

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tradephoric



Brian556

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

jakeroot

#102
Quote from: 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

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.

Quote from: Brian556 on June 02, 2015, 09:14:24 PM
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.

froggie

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.

tradephoric

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://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.


jeffandnicole

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.


Bickendan

Maybe all the Yield signs should be swapped out with full on Stop signs.
Seems to be drivers don't know what 'yield' means.

lordsutch

Quote from: 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.

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

jeffandnicole

Quote from: lordsutch on June 03, 2015, 12:55:53 PM
Quote from: 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.

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? 

Bickendan

Quote from: jeffandnicole on June 03, 2015, 01:09:32 PM
Quote from: lordsutch on June 03, 2015, 12:55:53 PM
Quote from: 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.

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.

lordsutch

Quote from: Bickendan on June 03, 2015, 02:22:06 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?

jakeroot

Quote from: 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.

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).

Bickendan

Quote from: lordsutch on June 03, 2015, 02:25:38 PM
Quote from: Bickendan on June 03, 2015, 02:22:06 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).

tradephoric

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:

QuoteWisconsin 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. 

tradephoric

Quote from: DaBigE on May 25, 2015, 01:52:02 AM
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.


DaBigE

Quote from: tradephoric on June 05, 2015, 01:28:08 PM
Quote from: DaBigE on May 25, 2015, 01:52:02 AM
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.
"We gotta find this road, it's like Bob's road!" - Rabbit, Twister

tradephoric

Quote from: 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.



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/

tradephoric

#117
Quote from: 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.

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://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.

Rothman

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.
Please note: All comments here represent my own personal opinion and do not reflect the official position(s) of NYSDOT.

tradephoric

Quote from: 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.

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)


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)



QuoteIn 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). 


tradephoric

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). 


Rothman

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
Please note: All comments here represent my own personal opinion and do not reflect the official position(s) of NYSDOT.

tradephoric

Quote from: 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!

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. 


jakeroot

Quote from: tradephoric on June 25, 2015, 03:19:53 PM
Quote from: 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!

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.

iBallasticwolf2

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.
Only two things are infinite in this world, stupidity, and I-75 construction



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