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Safety benefits of roundabouts

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Re: Safety benefits of roundabouts

#161

Post by InSteady »

Clamchop wrote: post #150
fnordpiglet wrote: post #147

Seattle roundabouts are absurd - they’re actually not roundabouts despite being shaped like them, but are traffic slow down artifacts. But people insist on treating them like roundabouts despite being too tight a radius for some cars and the city advising to not treat them as such.

Traffic calming features: https://en.m.wikipedia.org/wiki/Traffic_calming

We have lots of these little roundabouts in Portland (not to mention all manner of other traffic calming features), and they are generally well placed. Almost exclusively used in areas with heavy bike and pedestrian traffic, where cars would otherwise be incentivized to speed and bypass heavy traffic on nearby arterials and busy commute routes.

Re: Safety benefits of roundabouts

#162

Post by InSteady »

lumb63 wrote: post #38
sokoloff wrote: post #21

Earlier quoted context omitted.

Until you do what Cambridge, MA has done twice near my house: put a traffic light just outside the roundabout, so when the light turns red, traffic inevitably backs up through the roundabout, locking it up entirely. https://www.google.com/maps/@42.3875777,-71.1422076,18z?entr...

I can decisively say anyone advocating for roundabouts has not lived anywhere near Boston.

Let's be real, is this actually an indictment of roundabouts or is it just Boston?

Re: Safety benefits of roundabouts

#163

Post by macintux »

Symbiote wrote: post #120
pandaman wrote: post #103

Earlier quoted context omitted.

The protection is just by hiding half of the traffic beyond an obstacle, you can still get t-boned on the roundabout, but only by the cars from your right and not from both directions like on an intersection. I guess it's a plus but with the added danger of a head-on collision from people traversing the roundabout in the wrong way I won't say if it's net-positive safety-wise with any degree of confidence.

I have never seen anyone go the wrong way around a roundabout, and I've never heard anyone tell me they've seen it. It's so rare you can ignore it.

I’ve seen it, once. Fortunately the motorcycle rider coming the correct way spotted her in time.

Re: Safety benefits of roundabouts

#164

Post by dublinben »

yreg wrote: post #140
smeej wrote: post #135

Earlier quoted context omitted.

I think you're right about single vs. 2+ lanes. It doesn't matter how many diagram signs they put up before the roundabout entry, people will NOT understand a roundabout with more than one lane, and under no circumstance will people going straight through realize they have to yield to someone coming from the opposite side who's going 270° around the circle and exiting from the inner lane. Roundabouts are fine if the…

> people will NOT understand a roundabout with more than one lane We have tons of 2-lane ones and everyone understands them…

The number of drivers who think you can freely exit from the inner lane suggests otherwise.

Re: Safety benefits of roundabouts

#165

Post by InSteady »

swatcoder wrote: post #45
polemic wrote: post #31

Earlier quoted context omitted.

Roundabouts are great (and common where I live), but a downside is they can be difficult for pedestrians to cross. You need crossings that are set back from the exits, but this also makes it a longer path for the pedestrian.

Yes, they're absolutely horrid for pedestrians. Drivers anticipating their merge into roundabout are often too distracted to notice pedestrians intending to cross, and any pedestrian crossing the outflow of a roundabout can trigger a traffic backup that interferes with the flow of the circle itself and surprise drivers who expect it to stay moving. They have their benefits in some intersections, but they also have tr…

>Drivers anticipating their merge into roundabout are often too distracted to notice pedestrians intending to cross

This is so true that it happens constantly at a roundabout in my neighborhood that has stop signs and white stripes at the pedestrian crossing, right before the merge. Even people in the right turn only lane do it.

Re: Safety benefits of roundabouts

#166

Post by mhandley »

michaelteter wrote: post #141

Two lane roundabouts are pretty good. More than two lanes are very questionable. And roundabouts which include... stoplights!?!? are just stupid. I live in the Netherlands, where roundabouts are very common. In many cases, they are an improvement. But NL is also a huge bike country. And at most roundabouts, bikes have right of way. So as a car driver, you have to worry about other cars as well as bikes which may turn…

Under light to medium loads, roundabouts are preferable to junctions with stop lights, as you rarely need to wait long to enter the roundabout. But under high loads, they can cause starvation when there are no breaks in traffic along the more major road, so traffic cannot enter from the side road. When that happens, you need to add traffic lights to allow traffic to enter from the side road. But the traffic lights can be set up to only operate at busy times, so then you get the best of both worlds. Traffic lights on a roundabout at quiet times - yes, that's just stupid.

Re: Safety benefits of roundabouts

#167

Post by InSteady »

kieranmaine wrote: post #91
swatcoder wrote: post #45

Earlier quoted context omitted.

Yes, they're absolutely horrid for pedestrians. Drivers anticipating their merge into roundabout are often too distracted to notice pedestrians intending to cross, and any pedestrian crossing the outflow of a roundabout can trigger a traffic backup that interferes with the flow of the circle itself and surprise drivers who expect it to stay moving. They have their benefits in some intersections, but they also have tr…

I disagree. As a pedestrian, I only have to worry about cars coming from 2 directions (on to/off the roundabout) instead of 4 at an intersection. I'm confused by your comment that drivers merging into a roundabout are too distracted. As a driver merging into a roundabout I find I have far less cognitive load. I only have to look for pedestrians crossing in front of me and cars coming from the left. When coming off th…

At least if we are talking about the US, it is a fact that many drivers struggle and tunnel vision. Probably because they are so uncommon. It's great that you don't. Drivers that turn into drooling idiots may be the exception rather than the rule, but it happens frequently enough at the traffic circle in my neighborhood that I've learned to treat it with more caution than any other crossing in the entire city.

Re: Safety benefits of roundabouts

#168

Post by mikepurvis »

Clent wrote: post #148
olyjohn wrote: post #125

Earlier quoted context omitted.

Correct me if I'm wrong... but compared to a traffic light, you have to go significantly slower, so most accidents are not as severe as at a traffic light. You also aren't crashing into someone in a t-bone situation, usually they are sideswiped at more of an angle for less impact force. Of course someone could still fly into a roundabout at full speed. Anything is possible, but feel like think overall there still hav…

Correct. Anyone that says roundabouts are less safe doesn't have science backing their claim. While, they do not reduce the number of accidents and in some cases can increase accidents, but they consistently reduce the severity of the accidents. A three lane roundabout may be annoying when encounter as a tourist but the majority of locals going about their daily commutes quickly master them. For a three lane roundabo…

I would argue that the safety stats for them are still excessively car-centric. That is to say, roundabout collisions have better outcomes for car occupants specifically because they turn crashes into the kinds of crashes that cars handle best, which is low speed rear-endings, with the crumple zones doing all the heavy lifting to protect occupants.

I’m much more skeptical about how roundabout users fare when they are people walking or riding bicycles. At least in my city, we've had roundabouts for years, and the yield rate for pedestrians is ghastly— like, sub-50% of drivers stopping for someone waiting to cross and remaining fully stopped until the person is completely off the roadway. In theory this is a fine of hundreds of dollars ("failure to yield to crosswalk"), but it appears to receive basically zero enforcement in practice.

As a result, the fancy multi use paths that accompanied our roundabout installations get little use, since it's obvious to anyone who tries them how dangerous and unprotected they are.

Re: Safety benefits of roundabouts

#169

Post by peeters »

Enginerrrd wrote: post #107
devnull3 wrote: post #68

Simple roundabouts are definitely good but in UK I have found spiral roundabouts error prone if you have not driven on it before Example: [1] When visiting for the first time on a specific spiral roundabout: 1. Lane markings are faded 2. You do not know the specific lane unless you come very close to it and have to make a quick decision 3. Often due to queued traffic you cannot even see the lane marking until its too…

Transportation engineer here: Multi-lane roundabouts don't typically have any safety benefits. Single lane roundabouts do. Also, on the small side where you have traffic circles rather than roundabouts, those also suck.

> Multi-lane roundabouts don't typically have any safety benefits.

There seems to be quite a bit of literature that flatly disagrees with this statement. Perhaps you could add a source? The conventional wisdom where I'm from is that multilane roundabouts don't reduce the absolute number of crashes (and might even increase crash rates), but they still dramatically reduce the severity of crashes.

Canada:

> However recent data in the United States and Canada are showing that collision frequency at multi-lane roundabouts is often higher than expected, and sometimes higher than the prior signalized intersection. This trend is worrisome given that roundabouts are often constructed as a means of increasing safety. The good news is that fatal and injury crashes are almost always reduced with roundabouts, even if property-damage-only crashes are not.

https://www.tac-atc.ca/sites/default/files/conf_papers/weber...

Netherlands:

> Multi-lane roundabouts. These are less safe than single-lane roundabouts, but still safer than other types of intersection [22]. Multi-lane roundabouts are less safe because they have a larger number of conflict points, they are more complex, driving speed is higher, and they have a less sharp entry angle [23].

https://swov.nl/en/fact/roundabouts-how-safe-are-different-k...

US:

> Roundabouts force drivers to slow down and all but eliminate the most severe types of intersection crashes — right-angle, left-turn and head-on collisions. Single-lane roundabouts see fewer total crashes of any type.

https://www.iihs.org/news/detail/safety-at-two-lane-roundabo...

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