Comment by msandford | Hacker News Reader

Comment by msandford | Hacker News Reader

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One of the great advantages of roundabouts is that they're approximately "fair" whereas traffic lights are not.

What I mean is that a traffic light is very arbitrary and stops people who just barely didn't make the cutoff. Multiply that by 5, 10, or 20 traffic lights on a journey and an extra minute at each one can add up. So people have incentive to run the light and shave the 30 seconds or a minute. But then when people run the light, it slows down the cross-road who has to wait extra for the road to clear, despite it being "their turn". So then people on that side have an incentive to run the light, because they got wrongfully cutoff by the arbitrariness and the other jerks running the light first. Rinse and repeat for a few cycles and it's easy to see that this is not a good situation.

Traffic circles on the other hand don't suffer from this as there isn't arbitrariness on such a 'long' timescale. If you have to wait for a couple of extra cars it's only a few seconds, versus a minute or so. Because it's just a couple of seconds, people have less to lose and are more inclined to be nice. Which ultimately means that driving is more pleasant, even if it's not as efficient.

I also might disagree with the idea that roundabouts aren't effective at high traffic levels. https://www.youtube.com/watch?v=lwHfibl1AoI

The problem with roundabouts is starvation.

I grew up in France, which has more than 50% of the world's roundabouts. They are everywhere.

Where I am from, there is a roundabout at the intersection of a major road and a small road with little traffic. During rush hour, it is impossible to enter the roundabout coming from the small road because there is a continuous flow of cars coming from the major road. It is truly an uninterrupted flow of cars because the cars come from another roundabout...

Before the roundabout, there was no problem because there was a light that would be always be green for the main road expect when a car was detected on the small road. It was optimal.

Thanks for sharing! That makes sense that roundabout traffic flows can't be too lopsided or else you'll get this kind of behavior. It wasn't something I had ever thought of.

Couldn't you just put speed bumps at the entrances to the roundabout to ensure a gap between cars in this case?

Why don't we put a light at the entrance to the roundabout to create a gap between cars only when necessary?

Not a traffic engineer, but it is what I was told by Kiwis when driving in NZ, and it matched my experience. Driving a particular roundabout was a breeze at lunch (much better typically than a light), but took a very long time just to get into it during the 5pm rush.

Traffic lights have other trade-offs that can be tweaked such as timing length, it is hard to say what is best without knowing more.

Right, for sure! I'm not suggesting that my analysis is correct, it's just something I've noticed in a big city with a lot of traffic lights. Red-running is endemic during rush hour, but I see much better behavior at the roundabouts.

One of the bummers of traffic lights is that they tend to be more efficient with longer light cycles since you amortize the 'start up cost' of getting vehicles moving through the intersection over a longer period of vehicles moving at full speed. But the downside is that this increases the perceived unfairness because a one car length difference now means an even longer arbitrary delay.

I'm not a traffic engineer either but living in a city with horrible traffic it is something I think about.

Traffic lights with magnetic sensors to detect cars and amount of cars waiting work pretty well here in California. Unless you're riding a motorcycle...

Or a bicycle, which makes the lack of an Idaho Stop law even more frustrating.

Yeah. I know some motorcyclists who have gotten off their bike to walk to corner to push the crosswalk button to get the light to change. It may not be 100% legal, but you gotta do what you gotta do.

Now that is crazy, I just look around for cops a dozen times and floor it (carefully).

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