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Safety benefits of roundabouts

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Re: Safety benefits of roundabouts

#181

Post by bertil »

gumby wrote: post #170

Inexplicably, the ones in the Bay Area are often installed with stop signs, which makes the point of a roundabout rather mysterious.

You are meant to give priority to the vehicles in the roundabouts. A stop sign forces a two-second pause over yielding. I’m not sure that’s a big hindrance, and given how drivers barely mark stops and ignore yield signs, that might be the only way to get drivers to actually look if it’s free before they go on the roundabout.

The point is always to avoid frontal shocks by limiting intersecting paths and having instead merging lanes. Even with stop signs, those roundabouts do that.

Re: Safety benefits of roundabouts

#182

Post by pmontra »

mikepurvis wrote: post #168
Clent wrote: post #148

Earlier quoted context omitted.

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 ar…

I'm both a car driver and a cyclist. There are a zillion roundabouts in the country I'm living in. This is my experience and I'd like to hear a traffic designer about it.

Roundabouts feel safer than a 4 way intersecting when I'm in a car even if it's annoying to have to slow down and accelerate again when there is very little or no traffic, which is normal in the countryside. It also consumes more fuel, wears the car, adds to pollution.

It's different when I'm riding my bicycle. Roundabouts put me closer to cars, especially if there are traffic dividers that force cars closer to the side of the road. Then cars are usually slower than a bicycle in a small or medium sized roundabout (think of race bicycles with drop bars,) which adds up to chances of being packed between two cars. My feeling is that what's good for cars is bad for bicycles.

As a cyclist I can see what's around me much better than when I'm in my car. Intersections don't feel like a problem because of the extra visibility. When I'm riding I long for old times straight roads, with a line on the side and half a meter of asphalt on the other side to ride on. No roundabouts, no speed bumps especially the 3M style plastic ones, which I can jump but they are annoying. All those safety devices, including roundabouts, increase fatigue and danger. They are also the main reason for crashes in bicycle races but that's not an issue for normal people.

Finally, as I both drive and ride I know how to behave not to put in danger the cyclist. When I drive I don't overtake bicycles before a roundabout because they'll be at least as fast as me. I don't overtake when there is a short traffic divider which narrows the road. A long one, oh well, I have to. Same thing when I approach an intersection where I have to yield or stop. Bicycles will be definitely faster there because they can look around better than me and decide what to do quickly.

When I ride and I'm approaching a roundabout or entering a short narrowing of the road I look behind me and if it's safe I lean a little to the center of the road to prevent cars to overtake when they'll be forced to come close to me.

Re: Safety benefits of roundabouts

#183

Post by jameshart »

kazinator wrote: post #172
Enginerrrd wrote: post #107

Earlier quoted context omitted.

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.

All roundabouts prevent vehicles from just blowing straight through the intersection in the desired direction without so much as slowing down. They remove the middle part of the intersection where conflicting paths intersect. Two-lane roundabouts are larger; cars go around them faster. There is ambiguity. Some cars short-cut using the middle lane, and veer right out of it to their desired exit. Cars in the outer lane…

> All roundabouts prevent vehicles from just blowing straight through the intersection in the desired direction without so much as slowing down

Not at all. A large enough roundabout with good visibility from the approach can allow you to traverse it without slowing down at all - if the speed limits coming up to the yield line are appropriate, and traffic is flowing.

There's a sense in which a roundabout is just a short circular section of highway with a series of on and off-ramps around the edge. Well designed onramps allow you to merge without slowing, and off-ramps let you leave without disrupting traffic. Roundabouts can permit the same.

Re: Safety benefits of roundabouts

#184

Post by mitthrowaway2 »

eszed wrote: post #176
mitthrowaway2 wrote: post #132

Earlier quoted context omitted.

While you're here, can I ask you a question I've always wanted to ask about traffic circles? Perhaps this is also related to why they suck for safety. At least where I live, there are two rules for traffic circles: (1) yield to traffic that is already in the traffic circle, and (2) when two cars arrive at the same time, yield to traffic on your right . Rule 1 is the same as for a roundabout, but rule (2) is a bit str…

Just clarifying: you drive on the right-hand side of the road, so "right" for you means on the outside of the circle? Yeah, that seems mad.

Correct, right-hand side of the road.

Re: Safety benefits of roundabouts

#185

Post by mitthrowaway2 »

fshbbdssbbgdd wrote: post #178
mitthrowaway2 wrote: post #132

Earlier quoted context omitted.

While you're here, can I ask you a question I've always wanted to ask about traffic circles? Perhaps this is also related to why they suck for safety. At least where I live, there are two rules for traffic circles: (1) yield to traffic that is already in the traffic circle, and (2) when two cars arrive at the same time, yield to traffic on your right . Rule 1 is the same as for a roundabout, but rule (2) is a bit str…

They added some circular medians in the middle of 4-way stops where I live, are those traffic circles? Are you suggesting that when I get to a 4 way stop, whether I yield to traffic on the left or right should depend on whether the intersection has one of those medians in the middle? Personally I find it confusing that yielding works the opposite way on roundabouts and 4-way stops, and nobody else in my neighborhood…

In this case, they've removed the stop signs, so it's not a 4-way stop anymore, just a traffic circle.

Re: Safety benefits of roundabouts

#187

Post by kazinator »

jameshart wrote: post #183
kazinator wrote: post #172

Earlier quoted context omitted.

All roundabouts prevent vehicles from just blowing straight through the intersection in the desired direction without so much as slowing down. They remove the middle part of the intersection where conflicting paths intersect. Two-lane roundabouts are larger; cars go around them faster. There is ambiguity. Some cars short-cut using the middle lane, and veer right out of it to their desired exit. Cars in the outer lane…

> All roundabouts prevent vehicles from just blowing straight through the intersection in the desired direction without so much as slowing down Not at all. A large enough roundabout with good visibility from the approach can allow you to traverse it without slowing down at all - if the speed limits coming up to the yield line are appropriate, and traffic is flowing. There's a sense in which a roundabout is just a sho…

There is a recursive fix for that: put a small roundabout into each T shaped intersection of the huge roundabout.

Re: Safety benefits of roundabouts

#188

Post by WirelessGigabit »

Couple of things that go wrong with roundabouts:

2 lane roundabouts where the inner lane needs to give priority to then outer lane. The Netherlands does it a lot better with lanes that 'tear off', and you migrate naturally to the outside line.

Roundabouts on roads with lots of North/South traffic can cause people who come from East/West to have to wait forever as they can't just jump on the roundabout. As long as traffic is coming and can enter the roundabout they don't have to allow anybody else on it.

Re: Safety benefits of roundabouts

#189

Post by Too »

dublinben wrote: post #164
yreg wrote: post #140

Earlier quoted context omitted.

> 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.

They are right to. Simplified greatly, the further in the roundabout you are, the right of way is yours.

The exception is you can obviously not shoot straight from the left lane to the first exit.

In a 2 lane roundabout it is very simple. Enter in the left lane and you can exit 2nd or 3d, enter in the right lane and you can exit 1st or 2nd.

Where it gets complicated is roundabouts with 2 lane entry but only 1 lane in the third exit. Then you have to change lane right halfway through and be careful with people entering prematurely from your 1st exit, or people incorrectly staying in the right lane past the 2nd exit. It’s not always obvious but for those entering the rule is the same, since they enter after you, they should yield to you.

Re: Safety benefits of roundabouts

#190

Post by throwaway562if1 »

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.

Having lived in Boston and other areas with roundabouts, I can with confidence assert that this is a Boston traffic design problem, not a roundabout one.
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