Crash prone 'modern roundabouts'

[Sykotyk]

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".

[tradephoric]

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).

https://www.youtube.com/watch?v=xxkWMtAr4o8

[Brian556]

Quotew from        :

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.

[jakeroot]

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.

[lordsutch]

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 (see also: here; 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.

[tradephoric]

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

[jeffandnicole]

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.

[DaBigE]

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).

https://www.youtube.com/watch?v=xxkWMtAr4o8

Looks like the recently reconfigured DePere roundabout

[tradephoric]

Looks like the recently reconfigured DePere roundabout

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

[DaBigE]

Looks like the recently reconfigured DePere roundabout

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.

[UCFKnights]

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

[roadfro]

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.

[english si]

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.

[jakeroot]

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.

[jeffandnicole]

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.

[tradephoric]

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?

[tradephoric]

Here are back-to-back-to-back 3-lane roundabouts in Green Bay Wisconsin (all spirals  ).  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

[UCFKnights]

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.

[johndoe]

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.

[tradephoric]

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.

[jakeroot]

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.

[tradephoric]

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.

[DaBigE]

...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.

[tradephoric]

...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.

[tradephoric]

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:


160 FT central island diameter: