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Safety benefits of roundabouts

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Re: Safety benefits of roundabouts

#21

Post by sokoloff »

squarefoot wrote: post #8

Safety aside, roundabouts lower traffic significantly by never forcing cars to stop. Congestion increases as cars need to stop because of the inevitable latency propagating along the tails, and having more than one traditional intersections along the way can only make things even worse, so any solution to prevent cars from slowing down to a stop would mitigate those effects.

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...

Re: Safety benefits of roundabouts

#23

Post by zabzonk »

safety? bah! try going round the hanger lane gyratory system (west london, uk) in a triumph spitfire, at high speed, driven by a girl (my girlfriend at the time) who was too tiny to reach the pedals.

Re: Safety benefits of roundabouts

#24

Post by Maxion »

squarefoot wrote: post #8

Safety aside, roundabouts lower traffic significantly by never forcing cars to stop. Congestion increases as cars need to stop because of the inevitable latency propagating along the tails, and having more than one traditional intersections along the way can only make things even worse, so any solution to prevent cars from slowing down to a stop would mitigate those effects.

There is an issue with them though. If there is very unbalance traffic flow in one direction through the roundabout, traffic from the perpendicular direction tends to be perpetually forced to yield. And only being allowed in the roundabout by some graceful soul.

This can happen on routes where there are multiple chained roundabouts, that usually results in traffic coming at an even rate with no gaps in between.

Re: Safety benefits of roundabouts

#25

Post by macleginn »

squarefoot wrote: post #8

Safety aside, roundabouts lower traffic significantly by never forcing cars to stop. Congestion increases as cars need to stop because of the inevitable latency propagating along the tails, and having more than one traditional intersections along the way can only make things even worse, so any solution to prevent cars from slowing down to a stop would mitigate those effects.

With lively enough traffic, it’s not rare to see several cars waiting for their turn to enter the roundabout.

Re: Safety benefits of roundabouts

#26

Post by belorn »

squarefoot wrote: post #8

Safety aside, roundabouts lower traffic significantly by never forcing cars to stop. Congestion increases as cars need to stop because of the inevitable latency propagating along the tails, and having more than one traditional intersections along the way can only make things even worse, so any solution to prevent cars from slowing down to a stop would mitigate those effects.

Roundabouts often lead to cars being forced to stop. The stop is however generally much shorter, occasionally not needed, and when cars leaves at the first turn then the other cars from other directions can simultaneously use the roundabout at the same time. Many roundabouts here where I live also have extra roads for some direct right turns where such traffic flow is common, which mean that those cars don't even need to enter the roundabout and just need to be observant of cars existing towards the same direction.

Re: Safety benefits of roundabouts

#27

Post by ceejayoz »

gnicholas wrote: post #17

Interesting that there are no listed downsides. I saw a more balanced article a while back and recall that it listed cost (especially of the additional real estate, since roundabouts are larger) as being one downside. And in built-up cities, it's basically impossible to convert traditional intersections to roundabouts, because there's simply no room. It is nice to not have to pay for replacement signals, or have to d…

Cost is probably not a downside when you consider the cost of accidents.

Re: Safety benefits of roundabouts

#28

Post by marginalia_nu »

rwmj wrote: post #11

If you like roundabouts, try a roundabout of roundabouts: https://en.wikipedia.org/wiki/Magic_Roundabout_(Hemel_Hempst... This is near where I live and it is indeed safe, mainly because everyone drives incredibly slowly and cautiously since the experience is scary as hell.

Using roundabouts of roundabouts it's actually possible to build a 3 dimensional roundabout where traffic along the x, y and z axis can safely meet on the surface of a sphere.

Re: Safety benefits of roundabouts

#29

Post by Jtsummers »

hristov wrote: post #20

The greatest thing about roundabouts is that they protect against the idiot that goes through an intersection at full speed. He does that either because he is passed out behind the wheel or because he did not notice a stop sign and thought he had the right of way, or maybe because he just does not care. Well with a roundabout if you just go straight ahead you hit the center circle. Good roundabouts always have a slig…

As long as that center circle is high enough. I had a woman in a Toyota (Camry?) fly over one at about 45+mph and slam into me as I looped around it. Totaled her car, broke parts off my Explorer (repairable). Her son then tried to attack me with my bumper.

She kept insisting I turned in front of her (technically true, I was in a roundabout). She was arrested for drunk driving, and, later on, fined for all the flowers she damaged in the circle and the median she also ran over on her way into the intersection.

Re: Safety benefits of roundabouts

#30

Post by dfxm12 »

calimoro78 wrote: post #10

My experience is that roundabouts help but don't solve. E.g. if there is a complete traffic jam, you may actually increase the risk of collision due to negotiations about right of way happening every time a car can move forward. Some cities in Europe have so many roundabouts, and two or three lane roundabouts with complex exit decisions you need to make on a split second - it's actually very confusing to navigate.

You're never going to "solve" traffic problems when people are driving cars, but when you look at the data, crashes that lead to injuries and, importantly, fatalities, go down with roundabouts.

and two or three lane roundabouts with complex exit decisions you need to make on a split second - it's actually very confusing to navigate.

I think you're confusing what today might be called a "rotary" (?) with a modern roundabout. Whatever you call it, I don't think anyone builds what you're describing anymore.

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