Crash prone 'modern roundabouts'

[tradephoric]

It's not enough to say that the percentage of injury crashes at intersection B is lower so it must be safer.  Yes, roundabouts reduce crash severity but there's just so many more crashes occurring at these complex roundabouts that the actual number of injuries is roughly the same (as seen in the triple-lane roundabouts analyzed in the study which actually had more injury accidents than the before condition). 

You know, considering how much you hate it when people use single-lane roundabouts as a stand-in for all roundabouts when it comes to safety data, I'd have thought you would avoid using triple-lane roundabouts as a stand-in for all roundabouts.

I didn't say there's so many more crashes occurring at all roundabouts... i said there are so many more crashes occurring at these complex roundabouts.  I've always tried to preference my comments about high crash rates in regards to complex (2X2 and 3X2) roundabouts. 

[kphoger]

I didn't say there's so many more crashes occurring at all roundabouts... i said there are so many more crashes occurring at these complex roundabouts.  I've always tried to preference my comments about high crash rates in regards to complex (2X2 and 3X2) roundabouts. 

You're right, I didn't read your post carefully enough.  Sorry, there.

[tradephoric]

No worries, I still am opposed to single-lane roundabouts with fixed objects in the central island but that's a separate issue.  For the most parts single-lane roundabouts work well.  To that point, it looks like Toledo did a great job redesigning the Detroit/Cherry Street roundabout reducing it to one lane for the Cherry Street approach.  There's now no confusion how to navigate through the roundabout.


https://www.google.com/maps/@41.6859893,-83.5564183,116m/data=!3m1!1e3?entry=ttu

[tradephoric]

'Put a stoplight'; Man shares story after crashing at Maricopa County's worst intersection
https://www.12news.com/article/news/local/man-shares-story-after-crashing-at-maricopa-county-worst-intersection/75-61203028-076e-48a8-be79-11db4689d692

Most crashes of any intersection in Maricopa County is the 2x2 roundabout at 99TH Avenue & Lower Buckeye Road.  It had 411 crashes from 2017 thru 2021, which is 148 more crashes than the next most crash prone intersection in the county (67TH Avenue & Indian School Road).  Another example of a 2x2 roundabout failing at reducing crashes. I believe it's the only full blown 2x2 roundabout in the county which helps explain why there are so many more crashes at this complex roundabout compared to other multi-lane roundabouts in the county.


https://azmag.gov/Portals/0/Documents/TSC_2017-04-18_List-of-Top-100-Intersections-Ranked-by-Crash-Risk.pdf?ver=2021-01-27-083723-227

[Rothman]

'Put a stoplight'; Man shares story after crashing at Maricopa County's worst intersection
https://www.12news.com/article/news/local/man-shares-story-after-crashing-at-maricopa-county-worst-intersection/75-61203028-076e-48a8-be79-11db4689d692

Most crashes of any intersection in Maricopa County is the 2x2 roundabout at 99TH Avenue & Lower Buckeye Road.  It had 411 crashes from 2017 thru 2021, which is 148 more crashes than the next most crash prone intersection in the county (67TH Avenue & Indian School Road).  Another example of a 2x2 roundabout failing at reducing crashes. I believe it's the only full blown 2x2 roundabout in the county which helps explain why there are so many more crashes at this complex roundabout compared to other multi-lane roundabouts in the county.


https://azmag.gov/Portals/0/Documents/TSC_2017-04-18_List-of-Top-100-Intersections-Ranked-by-Crash-Risk.pdf?ver=2021-01-27-083723-227

So...Arizonans can't handle roundabouts.

[kalvado]

'Put a stoplight'; Man shares story after crashing at Maricopa County's worst intersection
https://www.12news.com/article/news/local/man-shares-story-after-crashing-at-maricopa-county-worst-intersection/75-61203028-076e-48a8-be79-11db4689d692

Most crashes of any intersection in Maricopa County is the 2x2 roundabout at 99TH Avenue & Lower Buckeye Road.  It had 411 crashes from 2017 thru 2021, which is 148 more crashes than the next most crash prone intersection in the county (67TH Avenue & Indian School Road).  Another example of a 2x2 roundabout failing at reducing crashes. I believe it's the only full blown 2x2 roundabout in the county which helps explain why there are so many more crashes at this complex roundabout compared to other multi-lane roundabouts in the county.


https://azmag.gov/Portals/0/Documents/TSC_2017-04-18_List-of-Top-100-Intersections-Ranked-by-Crash-Risk.pdf?ver=2021-01-27-083723-227

So...Arizonan DOT engineers can't handle roundabouts.

FTFY

[kphoger]

When a football team loses, it's always the coach's fault.

When a roundabout has a lot of crashes, it's always the engineer's fault.

[JREwing78]

I blame idiot drivers. Other countries do crazy things with roundabouts and don't seem to have nearly as much trouble.

[kalvado]

I blame idiot drivers. Other countries do crazy things with roundabouts and don't seem to have nearly as much trouble.

But they have better engineering by now...

[kphoger]

I blame idiot drivers. Other countries do crazy things with roundabouts and don't seem to have nearly as much trouble.

I'm not sure you can separate the two.  Engineering does not exist in a vacuum:  it exists within culture, and any roundabout design will play off that culture's history and values and expectations and norms.  It's possible that crazy roundabouts in other countries fare better because drivers in those other countries are better prepared—not by classroom instruction or personal discipline, but by aspects of their shared culture—to safely deal with them.  It's possible that some aspect of American culture just thwarts the safe performance of complex roundabout designs, no matter how well engineered they are.

I do find it strange that Americans have such trouble with well-designed, clearly marked, sufficiently signed multi-lane roundabouts—while drivers in third-world countries with practically zero drivers' education and much less strict traffic enforcement seem to have no trouble with poorly designed, unmarked multi-lane roundabouts.

[kalvado]

I blame idiot drivers. Other countries do crazy things with roundabouts and don't seem to have nearly as much trouble.

I'm not sure you can separate the two.  Engineering does not exist in a vacuum:  it exists within culture, and any roundabout design will play off that culture's history and values and expectations and norms.  It's possible that crazy roundabouts in other countries fare better because drivers in those other countries are better prepared—not by classroom instruction or personal discipline, but by aspects of their shared culture—to safely deal with them.  It's possible that some aspect of American culture just thwarts the safe performance of complex roundabout designs, no matter how well engineered they are.

I do find it strange that Americans have such trouble with well-designed, clearly marked, sufficiently signed multi-lane roundabouts—while drivers in third-world countries with practically zero drivers' education and much less strict traffic enforcement seem to have no trouble with poorly designed, unmarked multi-lane roundabouts.

Two things - proper signage, which is less than guaranteed; appropriate placement in terms of traffic volume; and proper design - especially size-wise.
There is a strong push for tiny roundabouts (because ROW) to handle more traffic than feasible. The result is, well, somewhat predictable

[kphoger]

There is a strong push for tiny roundabouts (because ROW) to handle more traffic than feasible. The result is, well, somewhat predictable

I seem to recall, maybe 15 or 20 years ago now, that the push for smaller roundabouts was being touted for safety benefits more than anything:  the smaller ICD made for lower speeds, which in turn made for safer performance.

[kalvado]

There is a strong push for tiny roundabouts (because ROW) to handle more traffic than feasible. The result is, well, somewhat predictable

I seem to recall, maybe 15 or 20 years ago now, that the push for smaller roundabouts was being touted for safety benefits more than anything:  the smaller ICD made for lower speeds, which in turn made for safer performance.

And I don't think I saw real research on that. Flipped trucks reports  suggest at least some wishful thinking  in lieu of information

[kphoger]

There is a strong push for tiny roundabouts (because ROW) to handle more traffic than feasible. The result is, well, somewhat predictable

I seem to recall, maybe 15 or 20 years ago now, that the push for smaller roundabouts was being touted for safety benefits more than anything:  the smaller ICD made for lower speeds, which in turn made for safer performance.

And I don't think I saw real research on that. Flipped trucks reports  suggest at least some wishful thinking  in lieu of information

You may be right about that.  My memory is fuzzy, but I don't remember seeing much research to go along with it either.

[JREwing78]

I blame idiot drivers. Other countries do crazy things with roundabouts and don't seem to have nearly as much trouble.

I'm not sure you can separate the two.  Engineering does not exist in a vacuum:  it exists within culture, and any roundabout design will play off that culture's history and values and expectations and norms.  It's possible that crazy roundabouts in other countries fare better because drivers in those other countries are better prepared—not by classroom instruction or personal discipline, but by aspects of their shared culture—to safely deal with them.  It's possible that some aspect of American culture just thwarts the safe performance of complex roundabout designs, no matter how well engineered they are.

I do find it strange that Americans have such trouble with well-designed, clearly marked, sufficiently signed multi-lane roundabouts—while drivers in third-world countries with practically zero drivers' education and much less strict traffic enforcement seem to have no trouble with poorly designed, unmarked multi-lane roundabouts.

Two things - proper signage, which is less than guaranteed; appropriate placement in terms of traffic volume; and proper design - especially size-wise.
There is a strong push for tiny roundabouts (because ROW) to handle more traffic than feasible. The result is, well, somewhat predictable

Anecdotally, the two main issues I see with folks navigating roundabouts:
- Not understanding who has right-of-way (i.e. the folks already in the roundabout)
- Not understanding what direction you can go from which lane.

The first problem is pure stupidity. I've never come across a roundabout that didn't have clear signage showing that people entering have to yield, and yet folks seem to have considerable trouble with that concept.

The second problem is a little more understandable - namely, cars already in the roundabout crossing paths because the inside lane tries to exit, but the outside lane tries to stay in the roundabout. Some of them angle the lanes in the roundabout to make it clearer which lane must exit, where the inside lane transitions outside. A lot of multi-lane roundabouts don't. If you sit someone down and make them think logically about how it works before they drive it, they're fine. But, on the spot, relying on instinct, they make the wrong decision. And, let's face it - most folks here driving roundabouts are relying on these faulty instincts.

It's a reflection on our driving culture - because we disinvested in public transportation 70 years ago in favor of the car, we have a whole group of people who have no business driving a car forced to do so. This lack of public transportation makes us hesitant to deny people access to driving, even when they're dangerous drivers who shouldn't be behind the wheel. Meanwhile, in places with robust public transportation, they can afford to be stingy about handing out a driver's license, and that tends to weed out bad drivers.

[kalvado]

I blame idiot drivers. Other countries do crazy things with roundabouts and don't seem to have nearly as much trouble.

I'm not sure you can separate the two.  Engineering does not exist in a vacuum:  it exists within culture, and any roundabout design will play off that culture's history and values and expectations and norms.  It's possible that crazy roundabouts in other countries fare better because drivers in those other countries are better prepared—not by classroom instruction or personal discipline, but by aspects of their shared culture—to safely deal with them.  It's possible that some aspect of American culture just thwarts the safe performance of complex roundabout designs, no matter how well engineered they are.

I do find it strange that Americans have such trouble with well-designed, clearly marked, sufficiently signed multi-lane roundabouts—while drivers in third-world countries with practically zero drivers' education and much less strict traffic enforcement seem to have no trouble with poorly designed, unmarked multi-lane roundabouts.

Two things - proper signage, which is less than guaranteed; appropriate placement in terms of traffic volume; and proper design - especially size-wise.
There is a strong push for tiny roundabouts (because ROW) to handle more traffic than feasible. The result is, well, somewhat predictable

Anecdotally, the two main issues I see with folks navigating roundabouts:
- Not understanding who has right-of-way (i.e. the folks already in the roundabout)
- Not understanding what direction you can go from which lane.

The first problem is pure stupidity. I've never come across a roundabout that didn't have clear signage showing that people entering have to yield, and yet folks seem to have considerable trouble with that concept.

The second problem is a little more understandable - namely, cars already in the roundabout crossing paths because the inside lane tries to exit, but the outside lane tries to stay in the roundabout. Some of them angle the lanes in the roundabout to make it clearer which lane must exit, where the inside lane transitions outside. A lot of multi-lane roundabouts don't. If you sit someone down and make them think logically about how it works before they drive it, they're fine. But, on the spot, relying on instinct, they make the wrong decision. And, let's face it - most folks here driving roundabouts are relying on these faulty instincts.

It's a reflection on our driving culture - because we disinvested in public transportation 70 years ago in favor of the car, we have a whole group of people who have no business driving a car forced to do so. This lack of public transportation makes us hesitant to deny people access to driving, even when they're dangerous drivers who shouldn't be behind the wheel. Meanwhile, in places with robust public transportation, they can afford to be stingy about handing out a driver's license, and that tends to weed out bad drivers.

There is a lot to say here...
First of all, using roundabout in excessive traffic locations results in inevitable reduction of safety margins. Drivers from the entry downstream of major one have to take chances into smaller gaps.
Second - yes, things have to be largely intuitive. Humans are pretty shitty in response  under stress, and looks like whatever had been known about that in 20th century is thoroughly forgotten. For one, a major US engineering company - Boeing - is pretty much in the toilet because they couldn't properly design "user interface" in fourth iteration of original 1960s design (737 max), nor showed institutional knowledge to build a solid case for UI of re-desing of 1990s design (777x)
Roundabouts follow similar scenario - things are designed without understanding normal human response. Then, of course, it's human fault...

[jakeroot]

Other countries do crazy things with roundabouts and don't seem to have nearly as much trouble.

Do we know this for sure?

[Occidental Tourist]

This is a poorly designed roundabout for the area, though, which is formerly rural transitioning to suburban with major routes emphasizing speed. The approach speed to this roundabout is 45 mph with no attempt at traffic calming before entry.  Two of the directions have driveways on the right just before the roundabout entrance, creating a driver distraction.  The design emphasizes continuity of speed for thru traffic by making thru movements subject to very little deviation angle.

They need to increase the deviation angle on entry as a start.

[kalvado]

This is a poorly designed roundabout for the area, though, which is formerly rural transitioning to suburban with major routes emphasizing speed. The approach speed to this roundabout is 45 mph with no attempt at traffic calming before entry.  Two of the directions have driveways on the right just before the roundabout entrance, creating a driver distraction.  The design emphasizes continuity of speed for thru traffic by making thru movements subject to very little deviation angle.

They need to increase the deviation angle on entry as a start.

The first question to ask is if there is actually enough benefits in going to a roundabout, or smaller changes, like adding turn lanes, have better cost-benefit ratio...

[ErmineNotyours]

I think I identified my least favorite roundabout implementation on a recent trip.
While driving Arizona 260 and 89A to Jerome I was subjected to something like 12 roundabouts in 17 miles while driving what was obstinately a highway. Much of the route had speed limits of 55 or 45 and every mile or two I had to slow down to screech through a roundabout with some minor road that likely had a fraction of the traffic.

I'm not a roundabout fan generally, but this had to be the worst implementation I have ever seen. Breaking up a major highway where I should be able to set the cruise at 65 and just go where I am going with a dozen of these stupid things. Canceling the cruise, slow down, speed up, etc. Its irritating, definitely wastes gasoline, and seems to serve no other purpose than be cheap and trendy compared to some proper interchanges. 

My current pet peeve is Washington SR 539: four roundabouts in 3.7 miles.  That and a creepy anti-abortion shrine means I have used I-5 or 542 + 9 for my travels to Canada for several years now.

[kphoger]

Other countries do crazy things with roundabouts and don't seem to have nearly as much trouble.

Do we know this for sure?

A question I've long wondered.  I haven't seen much, if any, data given in here for roundabouts outside the US.

[monty]

I've driven a couple thousand kilometers in Ireland where roundabouts are frequent. Driving on the (traditional American) "wrong" side of the road with a manual transmission requires a lot of focus. Multi lane roundabouts are common even on freeways. I'll just opine that drivers in Ireland were better than those in the US. They seemed to have a lot more patience even when I was in error. Dublin is a busy city but driving there still was a bit easier due just being around good drivers. My cabbie in Dublin and I had a good discussion on this topic.

[Rothman]

I've driven a couple thousand kilometers in Ireland where roundabouts are frequent. Driving on the (traditional American) "wrong" side of the road with a manual transmission requires a lot of focus. Multi lane roundabouts are common even on freeways. I'll just opine that drivers in Ireland were better than those in the US. They seemed to have a lot more patience even when I was in error. Dublin is a busy city but driving there still was a bit easier due just being around good drivers. My cabbie in Dublin and I had a good discussion on this topic.

Ireland:  Where both manners and curse words are king.

[tradephoric]

On December 12th, Caltrans had a ribbon cutting ceremony celebrating the completion of the State Route 184 Roundabout Project that was aimed to improve traffic safety.  Later that day Jose Guadalupe De La Paz was killed after his car struck the State Routes 223 and 184 roundabout at high speed flying airborne into a gas station pillar, cutting his vehicle in half.  The grim irony.

Caltrans' celebrated the completion of their State Route 184 Roundabout Project that aims to improve traffic safety
https://www.turnto23.com/news/in-your-neighborhood/arvin-lamont/changes-are-coming-for-drivers-in-lamont

Ribbon cutting that morning, fatal crash that night at new Weedpatch traffic roundabout
https://www.kget.com/news/local-news/ribbon-cutting-that-morning-fatal-crash-that-night-at-new-weedpatch-traffic-roundabout/

[Rothman]

I don't see the grim irony when someone hits the center of the roundabout at high speed, which would be more indicative of reckless/inattentive driving than a problem with the roundabout itself.  The driver could also have blown through a red light and hit another vehicle, possibly causing additional deaths.