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Crash prone 'modern roundabouts'

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

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kalvado

Quote from: jakeroot on July 04, 2020, 02:20:26 PM
^^^
So what benefits are there exactly, as compared to a standard left-hand "add lane" merge?

I suppose the curve makes it so that traffic slows down, allowing the off-ramp more chances to go, although that slowing could cause cars to "pile up" approaching the curve, making it just as hard to find gaps (especially if the approach road is a relatively straight, wide, high-speed arterial with heavy traffic).

There is a left-hand merge A4 in Surrey, BC seems to work pretty well.
I can see exit roundabout being a thing in certain suburban bedroom communities - it deprioritizes arterial through traffic compared to highway entry/exit traffic. May backfire once local area develops a bit and meaningful local traffic appears.


jakeroot

Quote from: kalvado on July 04, 2020, 02:55:44 PM
Quote from: jakeroot on July 04, 2020, 02:20:26 PM
^^^
So what benefits are there exactly, as compared to a standard left-hand "add lane" merge?

I suppose the curve makes it so that traffic slows down, allowing the off-ramp more chances to go, although that slowing could cause cars to "pile up" approaching the curve, making it just as hard to find gaps (especially if the approach road is a relatively straight, wide, high-speed arterial with heavy traffic).

There is a left-hand merge A4 in Surrey, BC seems to work pretty well.
I can see exit roundabout being a thing in certain suburban bedroom communities - it deprioritizes arterial through traffic compared to highway entry/exit traffic. May backfire once local area develops a bit and meaningful local traffic appears.

That would be my worry. Feels to me that it would eventually have to be signalized. Or maybe the non-yield entry having a signal/meter to reduce the amount of traffic that "left" turning off-ramp traffic would have to worry about.

Still, my gut tells me that a regular left-side add-lane would be better, assuming there's enough ROW. It could be a yield at first, same as the roundabout, and then signalized in the future.

tradephoric

I really like that left-hand merge A4 you linked and its questionable if that "partial" roundabout design would be in any way superior.  I'm just theorizing that a roundabout with the fewest number of conflict points would also have one of the lowest crash rates compared to other standard roundabouts.  It would be interesting if a few "partial" interchange roundabouts existed if nothing else just to research how safe they may be.

ErmineNotyours

Quote from: Mr. Matté on August 02, 2018, 07:25:40 PM
Quote from: Bruce on July 29, 2018, 10:29:26 PM
I wonder how crash-prone this roundabout is.

https://twitter.com/Streetfilms/status/1023739247826632705

Quote from: kalvado on July 30, 2018, 10:17:40 AM
Can we find any pedestrian-only roundabouts?

Of course New Jersey would have a bike lane with a jughandle:


Add to the list the intersection of the Woodland Trail and the Chehalis Western Trail in Lacey, Washington.  Google Satellite View.  It is signed with yield and roundabout arrows.  There were so many homeless people around that I didn't want to violate anyone's privacy by taking a picture, and it was worse when I came back at night.

plain

Quote from: ErmineNotyours on August 10, 2020, 09:32:51 PM
Quote from: Mr. Matté on August 02, 2018, 07:25:40 PM
Quote from: Bruce on July 29, 2018, 10:29:26 PM
I wonder how crash-prone this roundabout is.

https://twitter.com/Streetfilms/status/1023739247826632705

Quote from: kalvado on July 30, 2018, 10:17:40 AM
Can we find any pedestrian-only roundabouts?

Of course New Jersey would have a bike lane with a jughandle:


Add to the list the intersection of the Woodland Trail and the Chehalis Western Trail in Lacey, Washington.  Google Satellite View.  It is signed with yield and roundabout arrows.  There were so many homeless people around that I didn't want to violate anyone's privacy by taking a picture, and it was worse when I came back at night.

I'm glad that post got bumped. Has anyone found out where in NJ that bike lane jughandle is at yet?
Newark born, Richmond bred

tradephoric

Some interesting comments from Washtenaw County Road Commission engineer Mark McCulloch who was behind the very first roundabout cited on this thread: the State and Ellsworth roundabout in Ann Arbor. 

Quote"I never once imagined in my wildest imagination when we built it that we were going to have the number of fender bender noninjury crashes increase,"

Quote"We as engineers thought we are getting such great results with single lane roundabouts when it came to crash statistics and capacity analysis that we just thought automatically it was going to translate over into the multilane roundabouts,"

Quote"None of us, me included or the design engineers, had any idea [that] people were going to have complications with it,"

Quote"what we're just finding out is [that] when you add that second lane in there, it makes it not just literally [more] difficult but potentially exponentially more difficult for some drivers."

Quote"I'm optimistic in time with education and people becoming more familiar with roundabouts as more and more get built that that number can decrease. But [will it ever] get to fifty? I doubt it." (fifty referencing the fact that the feds consider any two-lane roundabout with over fifty crashes as high -- and State and Ellsworth averages 130). 

The Roundabout Drivers Hate

https://annarborobserver.com/s/the_roundabout_drivers_hate.html#.X0-2PNR7mK8



kalvado

Quote from: tradephoric on September 02, 2020, 11:29:35 AM
Some interesting comments from Washtenaw County Road Commission engineer Mark McCulloch who was behind the very first roundabout cited on this thread: the State and Ellsworth roundabout in Ann Arbor. 

Quote"I never once imagined in my wildest imagination when we built it that we were going to have the number of fender bender noninjury crashes increase,"

Quote"We as engineers thought we are getting such great results with single lane roundabouts when it came to crash statistics and capacity analysis that we just thought automatically it was going to translate over into the multilane roundabouts,"

Quote"None of us, me included or the design engineers, had any idea [that] people were going to have complications with it,"

Quote"what we're just finding out is [that] when you add that second lane in there, it makes it not just literally [more] difficult but potentially exponentially more difficult for some drivers."

Quote"I'm optimistic in time with education and people becoming more familiar with roundabouts as more and more get built that that number can decrease. But [will it ever] get to fifty? I doubt it." (fifty referencing the fact that the feds consider any two-lane roundabout with over fifty crashes as high -- and State and Ellsworth averages 130). 

The Roundabout Drivers Hate

https://annarborobserver.com/s/the_roundabout_drivers_hate.html#.X0-2PNR7mK8

Well... do they still require high school diploma to hold an engineering position at DOT?

jakeroot

#2507
Quote from: kalvado on September 02, 2020, 01:47:41 PM
Well... do they still require high school diploma to hold an engineering position at DOT?

I don't know if part of engineering education is being taught to think outside the box on a regular basis. Thinking inside the box is, apparently, drilled into you from day one: standards, standards, standards.

Relevant because all roundabouts are supposed to be good: they are something within the box to improve safety. Ergo, install them, and winner winner chicken dinner. Even if the FHWA-ignored reality is that multi-lane roundabouts actually suck.

kalvado

Quote from: jakeroot on September 02, 2020, 05:02:38 PM
Quote from: kalvado on September 02, 2020, 01:47:41 PM
Well... do they still require high school diploma to hold an engineering position at DOT?

I don't know if part of engineering education is being taught to think outside the box on a regular bases. Thinking inside the box is, apparently, drilled into you from day one: standards, standards, standards.

Relevant because all roundabouts are supposed to be good: they are something within the box to improve safety. Ergo, install them, and winner winner chicken dinner. Even if the FHWA-ignored reality is that multi-lane roundabouts actually suck.
That is a good thing for middle school, not so good for high school, and pretty poor for community college. I would think 2-year community college to be a bare minimum for holding those jobs, am I wrong?

jakeroot

I noticed (thanks to a link in another thread) that the southern roundabout at IN-265 and E 10th St in Utica, IN (just outside Jeffersonville) has meters for the two entrances from the north and west. I've seen meters at roundabouts before, but this seems to be both the only one with them installed from day one, and one of only a few with more than one entrance metered.

Indiana has other ramp meters (one example?) at roundabouts; Keystone Pkwy & Smokey Row in Carmel being one example. Other than using only post-mounted HAWK signals, it's an identical setup.

Has anyone seen this in operation? I'm curious how drivers treat the yield entry when traffic is stopped from their left. Must look like they're frozen in time or something :-D.

I also find it interesting that HAWK signals were used. The other Indiana example (in Carmel) uses HAWK signals, but WSDOT uses their standard ramp meter setup with a pole-mounted RYG signal directly above a smaller RYG signal facing the stop line.

Here's a shot. Side-note: this roundabout briefly has four lanes right before the gore area. Perhaps the only four-lane roundabout in the US?


cjw2001

#2510
I can see how the signals could be occasionally needed to avoid any backup of traffic onto the freeway.  The other thing that comes to mind would be if the signals are tied into the railroad crossing to help clear any backed up traffic on the crossing when a train approaches.   Likely that the signals don't get activated much unless one of the above scenarios arises.

Using HAWK signals makes sense as they can stay dark until needed, avoiding any unneeded confusion of a green light with the yield sign at the intersection to the roundabout.

CardInLex

Quote from: jakeroot on September 10, 2020, 02:47:31 PM
I noticed (thanks to a link in another thread) that the southern roundabout at IN-265 and E 10th St in Utica, IN (just outside Jeffersonville) has meters for the two entrances from the north and west. I've seen meters at roundabouts before, but this seems to be both the only one with them installed from day one, and one of only a few with more than one entrance metered.

Indiana has other ramp meters (one example?) at roundabouts; Keystone Pkwy & Smokey Row in Carmel being one example. Other than using only post-mounted HAWK signals, it's an identical setup.

Has anyone seen this in operation? I'm curious how drivers treat the yield entry when traffic is stopped from their left. Must look like they're frozen in time or something :-D.




I drive through frequently. I've never seen them in operation. But, I think they are more to do with the nearby rail crossing. My hypothesis: When RR is active, mainline has flashing red to keep roundabout clear. Then once the RR clears ramp gets flashing red to allow mainline backup to clear out.

cjw2001

Quote from: jakeroot on September 10, 2020, 02:47:31 PM

Has anyone seen this in operation? I'm curious how drivers treat the yield entry when traffic is stopped from their left. Must look like they're frozen in time or something :-D.


I've not been to this one in southern Indiana but I've experienced the scenario on the one in Carmel on the exit from Keystone Parkway.   Traffic is stopped far enough back from the intersection that it is fairly easy to tell that they aren't going anywhere.  Once the red light goes away it is easy enough to tell they are moving and then yield appropriately.  These signals are not activated that often other than as needed to prevent traffic backups onto northbound Keystone Parkway or on westbound Smoky Row.  On street view you can see the sensor on the pole that detects backed up traffic.    Typically this only happens during rush periods often synced with the mass amount of student traffic entering or leaving the nearby high school.  At most times of the day the roundabout handles fairly light traffic so the signals are not activated.   In the many many times I've used this exit ramp I've only seen the signals active a few times.

kphoger

Quote from: cjw2001 on September 10, 2020, 06:12:02 PM
Using HAWK signals makes sense as they can stay dark until needed, avoiding any unneeded confusion of a green light with the yield sign at the intersection to the roundabout.

An important confusion to avoid.
Keep right except to pass.  Yes.  You.
Visit scenic Orleans County, NY!
Male pronouns, please.

Quote from: Philip K. DickIf you can control the meaning of words, you can control the people who must use them.

jakeroot

Quote from: cjw2001 on September 10, 2020, 06:42:37 PM
Quote from: jakeroot on September 10, 2020, 02:47:31 PM

Has anyone seen this in operation? I'm curious how drivers treat the yield entry when traffic is stopped from their left. Must look like they're frozen in time or something :-D.


I've not been to this one in southern Indiana but I've experienced the scenario on the one in Carmel on the exit from Keystone Parkway.   Traffic is stopped far enough back from the intersection that it is fairly easy to tell that they aren't going anywhere.  Once the red light goes away it is easy enough to tell they are moving and then yield appropriately.  These signals are not activated that often other than as needed to prevent traffic backups onto northbound Keystone Parkway or on westbound Smoky Row.  On street view you can see the sensor on the pole that detects backed up traffic.    Typically this only happens during rush periods often synced with the mass amount of student traffic entering or leaving the nearby high school.  At most times of the day the roundabout handles fairly light traffic so the signals are not activated.   In the many many times I've used this exit ramp I've only seen the signals active a few times.

I can't help but think the two were installed as test subjects to see if they would be useful at other roundabouts. I think they're a great idea and make roundabouts potentially more useful when one of the entrances tends to flood the circle (a common issue at exceptionally busy roundabouts with only one or two entry lanes ... the three lane roundabouts seem to handle large volumes better, and may explain why the one in Utica is rarely activated.

Quote from: CardInLex on September 10, 2020, 06:12:36 PM
I drive through frequently. I've never seen them in operation. But, I think they are more to do with the nearby rail crossing. My hypothesis: When RR is active, mainline has flashing red to keep roundabout clear. Then once the RR clears ramp gets flashing red to allow mainline backup to clear out.

I don't dislike this theory, but that would also block cars from turning left towards Port Road and eastbound 265. I would think regular railway crossing signals and box markings would be superior? I mena, having traffic stop there will eventually result in a backup through the prior roundabout, and that would miss the point a bit.

cjw2001

Quote from: jakeroot on September 11, 2020, 12:22:38 PM

I can't help but think the two were installed as test subjects to see if they would be useful at other roundabouts. I think they're a great idea and make roundabouts potentially more useful when one of the entrances tends to flood the circle (a common issue at exceptionally busy roundabouts with only one or two entry lanes ... the three lane roundabouts seem to handle large volumes better, and may explain why the one in Utica is rarely activated.

The one at Smoky Row and Keystone Parkway was definitely installed to address a specific set of problems.   Prior to installation traffic would back up onto northbound Keystone Parkway during the evening rush hour and westbound Smoky Row traffic would back up during the school rush.   The signals have addressed both issues successfully.   

My gut feel is that these are probably activated a bit less now than when they were first installed due to the reduced traffic from Covid19 and the completion of the new interchange at 96th and Keystone (which removed the platoon effect of mass waves of synced traffic heading north on Keystone from the previous signal at 96th).    The great advantage of this solution is it doesn't affect traffic at all during normal roundabout operation and automatically responds only when needed to address an actual problem in progress.

jakeroot

Quote from: cjw2001 on September 11, 2020, 02:17:15 PM
Quote from: jakeroot on September 11, 2020, 12:22:38 PM

I can't help but think the two were installed as test subjects to see if they would be useful at other roundabouts. I think they're a great idea and make roundabouts potentially more useful when one of the entrances tends to flood the circle (a common issue at exceptionally busy roundabouts with only one or two entry lanes ... the three lane roundabouts seem to handle large volumes better, and may explain why the one in Utica is rarely activated.

The one at Smoky Row and Keystone Parkway was definitely installed to address a specific set of problems.   Prior to installation traffic would back up onto northbound Keystone Parkway during the evening rush hour and westbound Smoky Row traffic would back up during the school rush.   The signals have addressed both issues successfully.   

My gut feel is that these are probably activated a bit less now than when they were first installed due to the reduced traffic from Covid19 and the completion of the new interchange at 96th and Keystone (which removed the platoon effect of mass waves of synced traffic heading north on Keystone from the previous signal at 96th).    The great advantage of this solution is it doesn't affect traffic at all during normal roundabout operation and automatically responds only when needed to address an actual problem in progress.

I did not mean to imply that there were no reasons for the roundabout meters. Clearly, both roundabouts have a need for a meter. What I meant was more that these were being used as test dummies for other roundabouts, because they both have certain conditions that warranted some sort of experimentation. The one in Utica with the railway (potentially), and the one in Carmel because of the platooning effects from 96th, the nearby school, and the overall evening rush.

What I meant was more that the one in Utica was more about testing a large roundabout with meters, and the one in Carmel was more about testing a smaller roundabout with meters. Both are "interchange roundabouts" with at least one ramp having more or less constant flow conditions, but with one definitely needing it (Carmel) and the other perhaps not (Utica).

cjw2001

Quote from: jakeroot on September 11, 2020, 06:56:45 PM

I did not mean to imply that there were no reasons for the roundabout meters. Clearly, both roundabouts have a need for a meter. What I meant was more that these were being used as test dummies for other roundabouts, because they both have certain conditions that warranted some sort of experimentation. The one in Utica with the railway (potentially), and the one in Carmel because of the platooning effects from 96th, the nearby school, and the overall evening rush.


Yep I got that, was just adding detail for others.

Revive 755

Quote from: kalvado on September 02, 2020, 01:47:41 PM
Well... do they still require high school diploma to hold an engineering position at DOT?

Depending upon how "engineering position" is defined, a good number of states seem to require a four year degree, with some requiring licensure (or at least being on track for licensure in a certain amount of time).

Quote from: jakeroot on September 02, 2020, 05:02:38 PM
I don't know if part of engineering education is being taught to think outside the box on a regular basis. Thinking inside the box is, apparently, drilled into you from day one: standards, standards, standards.

Relevant because all roundabouts are supposed to be good: they are something within the box to improve safety. Ergo, install them, and winner winner chicken dinner. Even if the FHWA-ignored reality is that multi-lane roundabouts actually suck.

I think this applies in multiple situations where agencies get hung up on standards rather than taking a good look at the project/intersection in question.  It really gets bad when those agencies strongly stand by outdated internal standards which become in conflict with other standards that get updated such as the MUTCD.

jakeroot

File this under "overuse of roundabouts".

Can anyone explain what advantages this roundabout has over a traditional T-intersection? Traffic along the frontage road would still have priority even with a regular T-intersection. Only advantage that I can see might be traffic going slower and thus maybe easier to enter the roundabout from the "top" of the image. Still, traffic from the right has only just turned onto the road, so it's not like they're going very fast.

Near I-64 and Mason Road, just west of St Louis.


jakeroot

Quote from: Revive 755 on September 12, 2020, 11:46:46 AM
Quote from: jakeroot on September 02, 2020, 05:02:38 PM
I don't know if part of engineering education is being taught to think outside the box on a regular basis. Thinking inside the box is, apparently, drilled into you from day one: standards, standards, standards.

Relevant because all roundabouts are supposed to be good: they are something within the box to improve safety. Ergo, install them, and winner winner chicken dinner. Even if the FHWA-ignored reality is that multi-lane roundabouts actually suck.

I think this applies in multiple situations where agencies get hung up on standards rather than taking a good look at the project/intersection in question.  It really gets bad when those agencies strongly stand by outdated internal standards which become in conflict with other standards that get updated such as the MUTCD.

To be clear, I appreciate roadway standards. Without them, I'm sure we'd be in a very messy situation with our roads. Still, I really don't like "one size fits all" approaches to solving intersection problems, like roundabouts or DDIs, where they are installed with such great frequency that I have to assume they're dirt cheap. Otherwise, I feel like "spot improvements" are not given enough credit when it comes to improving issues like congestion or crash frequency.

kphoger

Quote from: jakeroot on September 16, 2020, 04:07:22 PM
File this under "overuse of roundabouts".

Can anyone explain what advantages this roundabout has over a traditional T-intersection? Traffic along the frontage road would still have priority even with a regular T-intersection. Only advantage that I can see might be traffic going slower and thus maybe easier to enter the roundabout from the "top" of the image. Still, traffic from the right has only just turned onto the road, so it's not like they're going very fast.

Near I-64 and Mason Road, just west of St Louis.




1.  It could theoretically allow a free-flowing two-lane right turn out of the hospital parking lot–except that isn't the way they striped and signed it.

2.  It lets southbound traffic on Mason Road skirt around a red light by turning right with a Yield sign, going around the circle, and then turning right on red.   :)
Keep right except to pass.  Yes.  You.
Visit scenic Orleans County, NY!
Male pronouns, please.

Quote from: Philip K. DickIf you can control the meaning of words, you can control the people who must use them.

jakeroot

Quote from: kphoger on September 16, 2020, 04:19:34 PM
1.  It could theoretically allow a free-flowing two-lane right turn out of the hospital parking lot–except that isn't the way they striped and signed it.

2.  It lets southbound traffic on Mason Road skirt around a red light by turning right with a Yield sign, going around the circle, and then turning right on red.   :)

Based on your reply...I'm keeping it filed under "overuse" :-D.

CardInLex

Quote from: jakeroot on September 16, 2020, 05:18:14 PM
Quote from: kphoger on September 16, 2020, 04:19:34 PM
1.  It could theoretically allow a free-flowing two-lane right turn out of the hospital parking lot–except that isn't the way they striped and signed it.

2.  It lets southbound traffic on Mason Road skirt around a red light by turning right with a Yield sign, going around the circle, and then turning right on red.   :)

Based on your reply...I'm keeping it filed under "overuse" :-D.

Google Maps places a bus stop marker on the outside of the roundabout. Perhaps it's to allow busses turning off southbound Mason Road to drop off at the health facility and then turn back to resume going south on Mason. But that's just a guess.

jakeroot

Quote from: CardInLex on September 16, 2020, 05:44:37 PM
Quote from: jakeroot on September 16, 2020, 05:18:14 PM
Quote from: kphoger on September 16, 2020, 04:19:34 PM
1.  It could theoretically allow a free-flowing two-lane right turn out of the hospital parking lot–except that isn't the way they striped and signed it.

2.  It lets southbound traffic on Mason Road skirt around a red light by turning right with a Yield sign, going around the circle, and then turning right on red.   :)

Based on your reply...I'm keeping it filed under "overuse" :-D.

Google Maps places a bus stop marker on the outside of the roundabout. Perhaps it's to allow busses turning off southbound Mason Road to drop off at the health facility and then turn back to resume going south on Mason. But that's just a guess.

That would actually be quite plausible. But I did check Metro St Louis's route map, and the 65 runs along the frontage road, rather than along Mason. Route 57X uses Mason, but the closest stop is at Masonridge Rd on the other side of the interchange. Plus, it goes to and from downtown via 64, so it doesn't run past the health facility anyways.



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