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Safety benefits of roundabouts

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Re: Safety benefits of roundabouts

#131

Post by gnicholas »

ghaff wrote: post #96
kieranmaine wrote: post #91

Earlier quoted context omitted.

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…

It depends on the roundabout. A low traffic, single-lane roundabout is pretty straightforward. There are also heavy traffic two-lane roundabouts in my area. One is pretty much impossible for a pedestrian to traverse. (Not that it's in a pedestrianized area anyway.) The other two can only be traversed at relatively nearby traffic lights.

I see near-accidents all the time, when a driver is stopped at the entrance to a roundabout, looking left at the cars, and then a pedestrian (or more likely, a cyclist/escooter rider) comes from the right. The driver starts going when there's a clearing in the cars, before realizing that there's someone approaching from the right (I'm in the US, so cars are approaching from the left).

Re: Safety benefits of roundabouts

#132

Post by mitthrowaway2 »

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.

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 strange when the two are put together. It creates a scenario where if the leftmost car doesn't yield for whatever reason (perhaps they thought they arrived a microsecond earlier), then now they move forward and become "traffic in the traffic circle", which means they steal priority and the right-most car now has to yield to them. If the rule were flipped the other way, such that we default to always yielding to the car on the left, then this wouldn't happen; it would work just like a roundabout, and the order of yielding priority would be the same regardless of agreement on the exact timing of when each car arrived at the traffic circle.

So, why is it that at a traffic circle we yield to traffic on the right, rather than the left? Is it just to be consistent with 4-way stops?

Re: Safety benefits of roundabouts

#133

Post by DeRock »

oldbbsnickname wrote: post #127

Roundabouts for high traffic areas are good. The problem is when they are overused in low traffic areas where they create obstacles to efficient continuous motion, increase pollution, and waste time. PS: One place that doesn't do proper traffic design (or architecture): Texas. They insist on placing massive concrete dividers everywhere and have camouflaged by wear obstacles in the middle of paths that are injurious t…

> The problem is when they are overused in low traffic areas where they create obstacles to efficient continuous motion, increase pollution, and waste time.

The alternative (at least from my experience in the US) is a 4-way stop, and is worse for all those criteria.

Re: Safety benefits of roundabouts

#134

Post by city41 »

halfmatthalfcat wrote: post #105

Long time Carmel, IN resident here, AMA. Yes, almost every intersection has a roundabout for a population around 100k. Yes, they are efficient. Yes, it’s a pain using them when people who don’t know how to use them, use them.

> Yes, it’s a pain using them when people who don’t know how to use them, use them.

Here in Michigan there are roundabouts everywhere. And I'd estimate oh maybe 20% of the drivers know how to use them. Because of that, I absolutely hate them.

A roundabout around here is just a total luck of the draw on what you will get: people treating it like a four way stop, people ignoring it completely and just blasting straight through at top speed, people going into the roundabout then stopping at every merge point, people going into the roundabout and stopping to let someone else merge in front of them, on and on. I'm still amazed at what people do.

I suspect the people who blast through it at top speed and cause an accident cause other people to turn into the type that treat roundabouts with extreme caution.

Just outside my neighborhood I must have seen 10 accidents in the past two years alone. That's a lot of accidents at an otherwise low traffic intersection.

Re: Safety benefits of roundabouts

#135

Post by smeej »

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.

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 rule is, "Just get in there without hitting anybody and go around until you're ready to leave," but expecting anything more than that from most drivers is a lost cause.

Re: Safety benefits of roundabouts

#136

Post by Zanni »

Here's an explainer on "conflict points" [1] which seems central to the argument. Most folks intuitions are correct that roundabouts eliminate cross-traffic (major conflicts), but they also reduce merge, diverge and weave conflicts (minor).

[1] https://www.apsed.in/post/conflict-points-at-intersection

Re: Safety benefits of roundabouts

#137

Post by gruez »

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.

>Transportation engineer here: Multi-lane roundabouts don't typically have any safety benefits. Single lane roundabouts do.

Source? Not doubting you, just want something to reference in the future.

Re: Safety benefits of roundabouts

#138

Post by JohnFen »

kibwen wrote: post #109
JohnFen wrote: post #104

Earlier quoted context omitted.

Multilane roundabouts in my part of the US are absolutely terrifying because people don't know how to use them. Accidents and close calls are amazingly common. As a result, I drive out of my way to ensure that I avoid them. Simple roundabouts are fine.

As a bicyclist, I avoid multi-lane roundabouts like my life depends on it... because it does. Utterly nightmarish experience. This is why I despair every time someone is like "let's build more roundabouts in the US!" No, what you're missing is that all our roads are already too wide and all we get are multi-lane roundabouts, which are worse than intersections. At least at an intersection, I can see that one lane of t…

I bike as my primary transportation, and there's literally no chance that I'd dare to bike through a roundabout. Seems like a recipe for serious injury or death to me.

Fortunately, I live in one of the few US cities that really are bike-friendly, so 90% of the time I'm on a bike path that is physically separated from where cars go.

Re: Safety benefits of roundabouts

#139

Post by [deleted] »

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.

[deleted]

Re: Safety benefits of roundabouts

#140

Post by yreg »

smeej wrote: post #135
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.

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…

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