Crash prone 'modern roundabouts'

[webny99]

Yet, in the table posted, every single roundabout listed had crashes go down from 2019 to 2020...

Very easily explained by the fact that traffic overall went way down in 2020.

[kalvado]

Yet, in the table posted, every single roundabout listed had crashes go down from 2019 to 2020...

Very easily explained by the fact that traffic overall went way down in 2020.

possibly  adding even steeper reduction of long haul traffic, with non-locals more likely to run into a problem with unexpected road configurations.

[skluth]

So your citation is a ridiculous made up example?

What about the time the driver blows through the intersection but there are multiple other cars already in it?

Like this crash that killed 6 at 1:40pm

I mean, I guess I could post a video about an incident in which nothing happened, but you know what, nobody makes news stories about that.

OK, you want a non-hypothetical, non-made-up example?  I've personally blown through a red light while crossing Michigan Avenue just north of downtown Chicago.  I had grown up in a small town, was a bit overwhelmed by city traffic, and neglected to notice the red light.  You know what happened?  Nothing.  I think a CTA bus honked at me, and that was it.  Forgive me if I can't link to a news story about it.  So yeah, I ran straight through a red light at a busy intersection in one of the nation's most crowded cities, and there were zero injuries.

Congratulations on surviving. I've done the same in St Louis and I actually lived there at the time. It's called dumb luck. My Uncle Jimmy was just out of high school when he was thrown from his car in an accident; his car was crushed and he would have died had he worn his seat belt. He used this as an excuse to never wear his seat belt as he claimed that seat belts killed people. Statistics say he was lucky and was the exception to the norm. Your argument is meaningless unless you can cite evidence that your statement is true. Anecdotes alone mean nothing and will be ignored.

[kalvado]

So your citation is a ridiculous made up example?

What about the time the driver blows through the intersection but there are multiple other cars already in it?

Like this crash that killed 6 at 1:40pm

I mean, I guess I could post a video about an incident in which nothing happened, but you know what, nobody makes news stories about that.

OK, you want a non-hypothetical, non-made-up example?  I've personally blown through a red light while crossing Michigan Avenue just north of downtown Chicago.  I had grown up in a small town, was a bit overwhelmed by city traffic, and neglected to notice the red light.  You know what happened?  Nothing.  I think a CTA bus honked at me, and that was it.  Forgive me if I can't link to a news story about it.  So yeah, I ran straight through a red light at a busy intersection in one of the nation's most crowded cities, and there were zero injuries.

Congratulations on surviving. I've done the same in St Louis and I actually lived there at the time. It's called dumb luck. My Uncle Jimmy was just out of high school when he was thrown from his car in an accident; his car was crushed and he would have died had he worn his seat belt. He used this as an excuse to never wear his seat belt as he claimed that seat belts killed people. Statistics say he was lucky and was the exception to the norm. Your argument is meaningless unless you can cite evidence that your statement is true. Anecdotes alone mean nothing and will be ignored.

Evidence of what exactly do you want?
That high speed red light violation can be survivable with some luck? There are some examples above, so it is proven by presented  evidence. Pretty obvious that less traffic means better chances.
Evidence of hard feature in vehicle path greatly reduces survival chance? Again, fairly obvious. If you notice, they rarely - if ever - use concrete jersey barriers across the traffic path.  Exception may be something like T intersection at the edge of a cliff, where crash into concrete may be more survivable than 100s feet fall.
Most concrete barriers are parallel or low angle for lane separation and lane drop, and tested to 15 degree impact. Barriers across traffic are usually collapsible -  barrels, metal rail, some frames - to give driver a better chance in case of a crash.

If you see many opposing examples on the road, this is because your local DOT is not doing things right. And hard feature in the roundabout is against these approaches...

[Scott5114]

Hmm. I wonder what would happen if you put a freeway-style cable barrier in a loop around the center island of a roundabout? (Probably won't work, because those probably aren't designed to catch a vehicle hitting it at a 90° angle, but...)

[jakeroot]

Yet, in the table posted, every single roundabout listed had crashes go down from 2019 to 2020...

Very easily explained by the fact that traffic overall went way down in 2020.

The context was that fatalities increased from 2019 to 2020 despite total traffic dropping.

[webny99]

Yet, in the table posted, every single roundabout listed had crashes go down from 2019 to 2020...

Very easily explained by the fact that traffic overall went way down in 2020.

The context was that fatalities increased from 2019 to 2020 despite total traffic dropping.

However, that was in total, not specific to roundabouts.

[interstatefan990]

Does anyone else think this "roundabout" could use better signage and/or design?

[cjw2001]

Does anyone else think this "roundabout" could use better signage and/or design?

This thread is about modern roundabouts, and that definitely isn't one.

[jakeroot]

Does anyone else think this "roundabout" could use better signage and/or design?

This thread is about modern roundabouts, and that definitely isn't one.

That may be his point, though. It's definitely an older traffic-circle design from the early half of the 20th century and probably could use better signage and potentially overall design.

I think modifying that circle into a roundabout (improving approach angles, center island location adjustment) and maybe installing a second roundabout at Marvin / Calf Pasture Beach could make for a great double roundabout intersection.

[kalvado]

Does anyone else think this "roundabout" could use better signage and/or design?

This thread is about modern roundabouts, and that definitely isn't one.

That may be his point, though. It's definitely an older traffic-circle design from the early half of the 20th century and probably could use better signage and potentially overall design.

I think modifying that circle into a roundabout (improving approach angles, center island location adjustment) and maybe installing a second roundabout at Marvin / Calf Pasture Beach could make for a great double roundabout intersection.

I would say it could use some design to begin with. Looks like a low traffic area, so its unclear why they bothered to do anything at all. Someone had to defend a thesis?

[interstatefan990]

Does anyone else think this "roundabout" could use better signage and/or design?

This thread is about modern roundabouts, and that definitely isn't one.

That may be his point, though. It's definitely an older traffic-circle design from the early half of the 20th century and probably could use better signage and potentially overall design.

I think modifying that circle into a roundabout (improving approach angles, center island location adjustment) and maybe installing a second roundabout at Marvin / Calf Pasture Beach could make for a great double roundabout intersection.

Agreed. And yeah, I just think it's confusing as heck because it's a normal traffic circle except it functions almost as a reverse roundabout, because traffic inside the circle yields to traffic entering the circle, save for the stop sign on one of the Gregory Boulevard approaches. There's also no yield sign at all for traffic on Marvin St continuing straight on to 5th St, crossing Gregory Boulevard in the process.

[jakeroot]

I would say it could use some design to begin with. Looks like a low traffic area, so its unclear why they bothered to do anything at all. Someone had to defend a thesis?

Seems to have been built in the 1920s, maybe earlier. I'm not sure how traffic engineering worked back then, if I'm honest.

...And yeah, I just think it's confusing as heck because it's a normal traffic circle except it functions almost as a reverse roundabout, because traffic inside the circle yields to traffic entering the circle, save for the stop sign on one of the Gregory Boulevard approaches. There's also no yield sign at all for traffic on Marvin St continuing straight on to 5th St, crossing Gregory Boulevard in the process.

I assume traffic only yields inside the circle to traffic entering from Marvin? The other approaches are either stop signs entering the circle or no signs at all.

The obvious solution is just to install yield signs at all of the entries with supplemental "to traffic on left" signage.

[Scott5114]

Also I have to laugh at the way 89 Gregory Blvd. there is blurred out, which caused me to Google it to see if there's anything special about it (there's not), which I wouldn't have done if they had left it unblurred.

[interstatefan990]

I assume traffic only yields inside the circle to traffic entering from Marvin? The other approaches are either stop signs entering the circle or no signs at all.

Well, "yield" in the sense that by law you have to let other cars go first even if there's no sign. If you were traveling in the direction that the camera is pointed here, I assume you'd have to yield to traffic coming from your right.

The obvious solution is just to install yield signs at all of the entries with supplemental "to traffic on left" signage.

Yes, that seems like the most cost-effective solution if converting it into a traditional roundabout isn't an option. I have to admit, I did get honked at for slowing down when I first drove through here going southbound on Gregory, as I wasn't sure if there was a missing YIELD sign on one of the approaches, or if I was supposed to yield at all.

[interstatefan990]

Also I have to laugh at the way 89 Gregory Blvd. there is blurred out, which caused me to Google it to see if there's anything special about it (there's not), which I wouldn't have done if they had left it unblurred.

Right? This isn't Germany.

[CovalenceSTU]

On the subject of modern roundabouts, I can say from experience that the biggest problem with the US 101/OR 202 roundabout (mentioned towards the start of the thread) is that the 101S entrance/exit are too close together, meaning that unless you signal left people frequently don't react fast enough to stop:



At 20mph (29-30 ft/s) that means that 101S has a full second less to react vs. 101N, and only around 2 seconds to see a car going around and stop. The solution would be to move the 101S exit farther back in the roundabout, which would add that ≈1 second of reaction time (and also extend the solid line, there's functionally no reason for traffic in the circle to cross to the right lane). MS Paint mockup of what it could look like:

[jakeroot]

I assume traffic only yields inside the circle to traffic entering from Marvin? The other approaches are either stop signs entering the circle or no signs at all.

Well, "yield" in the sense that by law you have to let other cars go first even if there's no sign. If you were traveling in the direction that the camera is pointed here, I assume you'd have to yield to traffic coming from your right.

True. Without signage, roundabouts would always require circulating traffic to yield as entering traffic is 'from the right' and by law has right-of-way.

The obvious solution is just to install yield signs at all of the entries with supplemental "to traffic on left" signage.

Yes, that seems like the most cost-effective solution if converting it into a traditional roundabout isn't an option. I have to admit, I did get honked at for slowing down when I first drove through here going southbound on Gregory, as I wasn't sure if there was a missing YIELD sign on one of the approaches, or if I was supposed to yield at all.

I would have instinctively slowed and yielded as well.

It should be noted that satellite imagery shows edge extension (usually yield) markings along the entrances from both Gregory and Marvin, despite both of these ostensibly having right-of-way in street view imagery. Curious if something has changed lately that isn't shown in street view.

[interstatefan990]

It should be noted that satellite imagery shows edge extension (usually yield) markings along the entrances from both Gregory and Marvin, despite both of these ostensibly having right-of-way in street view imagery. Curious if something has changed lately that isn't shown in street view.

What's even more interesting is when I drove through, I think I remember a thin solid white line across one of the Gregory entrances, continuing out from the white line on the top of the yellow striped area that delineates the circle. Don't quote me on that, though. Classic CT road design.

[jakeroot]

On the subject of modern roundabouts, I can say from experience that the biggest problem with the US 101/OR 202 roundabout (mentioned towards the start of the thread) is that the 101S entrance/exit are too close together, meaning that unless you signal left people frequently don't react fast enough to stop:

...
At 20mph (29-30 ft/s) that means that 101S has a full second less to react vs. 101N, and only around 2 seconds to see a car going around and stop. The solution would be to move the 101S exit farther back in the roundabout, which would add that ≈1 second of reaction time (and also extend the solid line, there's functionally no reason for traffic in the circle to cross to the right lane). MS Paint mockup of what it could look like:

This is...interesting.

Generally, roundabout exits are meant to be slightly higher speed than entrances, but still have some deflection to ensure traffic doesn't exit so fast as to decrease the chance of yielding to crossing pedestrians.

Your design does have a much flatter exit (meaning, higher speed) than present, and does have the added benefit of distancing the exit and entrance enough that traffic coming from 101 would have greater warning of traffic continuing to circulate, and would be able to keep moving more often. But that may have a detrimental impact on traffic coming from 202, who now has to contend with traffic entering at a higher and more continuous rate.

I would also argue that most roundabouts, particularly single-lane roundabouts, don't have exceptional distance between the exit and entrance legs. I.e., this is a fairly normal issue for most roundabouts.

[kalvado]

On the subject of modern roundabouts, I can say from experience that the biggest problem with the US 101/OR 202 roundabout (mentioned towards the start of the thread) is that the 101S entrance/exit are too close together, meaning that unless you signal left people frequently don't react fast enough to stop:

...
At 20mph (29-30 ft/s) that means that 101S has a full second less to react vs. 101N, and only around 2 seconds to see a car going around and stop. The solution would be to move the 101S exit farther back in the roundabout, which would add that ≈1 second of reaction time (and also extend the solid line, there's functionally no reason for traffic in the circle to cross to the right lane). MS Paint mockup of what it could look like:

This is...interesting.

Generally, roundabout exits are meant to be slightly higher speed than entrances, but still have some deflection to ensure traffic doesn't exit so fast as to decrease the chance of yielding to crossing pedestrians.

Your design does have a much flatter exit (meaning, higher speed) than present, and does have the added benefit of distancing the exit and entrance enough that traffic coming from 101 would have greater warning of traffic continuing to circulate, and would be able to keep moving more often. But that may have a detrimental impact on traffic coming from 202, who now has to contend with traffic entering at a higher and more continuous rate.

I would also argue that most roundabouts, particularly single-lane roundabouts, don't have exceptional distance between the exit and entrance legs. I.e., this is a fairly normal issue for most roundabouts.

Pedestrian crosswalks don't belong within at least 100' from roundabout. Of course, an urge to use a cool design pushes safety to a back burner...

[jakeroot]

On the subject of modern roundabouts, I can say from experience that the biggest problem with the US 101/OR 202 roundabout (mentioned towards the start of the thread) is that the 101S entrance/exit are too close together, meaning that unless you signal left people frequently don't react fast enough to stop:

...
At 20mph (29-30 ft/s) that means that 101S has a full second less to react vs. 101N, and only around 2 seconds to see a car going around and stop. The solution would be to move the 101S exit farther back in the roundabout, which would add that ≈1 second of reaction time (and also extend the solid line, there's functionally no reason for traffic in the circle to cross to the right lane). MS Paint mockup of what it could look like:

This is...interesting.

Generally, roundabout exits are meant to be slightly higher speed than entrances, but still have some deflection to ensure traffic doesn't exit so fast as to decrease the chance of yielding to crossing pedestrians.

Your design does have a much flatter exit (meaning, higher speed) than present, and does have the added benefit of distancing the exit and entrance enough that traffic coming from 101 would have greater warning of traffic continuing to circulate, and would be able to keep moving more often. But that may have a detrimental impact on traffic coming from 202, who now has to contend with traffic entering at a higher and more continuous rate.

I would also argue that most roundabouts, particularly single-lane roundabouts, don't have exceptional distance between the exit and entrance legs. I.e., this is a fairly normal issue for most roundabouts.

Pedestrian crosswalks don't belong within at least 100' from roundabout. Of course, an urge to use a cool design pushes safety to a back burner...

Speeds are too high 100 feet from a roundabout, better to use crosswalks at the entry/exit legs. Pedestrians will not detour that far anyways.

[interstatefan990]

Isn't pedestrian traffic near roundabouts pretty low to start with? Since they're usually built in less densely populated areas or blend in with car-centric road design?

[kalvado]

Isn't pedestrian traffic near roundabouts pretty low to start with? Since they're usually built in less densely populated areas or blend in with car-centric road design?

You wish. US is a free country, so road designers are not bound by stupid rules, and roundabout in pedestrian core is a cool feature! (right at the top of crash intersection list.)

Actually after all the limitations are properly considered, roundabout use case ends up so rasor thin that they shouldn't be considered a mainstream approach.
Limitations an left turn capacity, on projected traffic growth, pedestrian presence, trucks percentage, speeds... No real scaling options....
There is a thread on fourth traffic light phase where cooperating autonomous vehicles can make use of cooperative yielding and small gaps. That is where roundabouts may shine... Although my feeling is juggling with wineglasses would be an easier and safer task.

[tradephoric]

Relatively new I-95 interchange roundabout outside Richmond saw a serious crash that injured 6 people.  A passenger car crashed head-first into a tractor-trailer.

https://www.wric.com/news/local-news/richmond/six-people-injured-in-head-on-tractor-trailer-crash-at-maury-roundabout/