An engineer's design of intersections that require no traffic lights | Hacker News Reader

An engineer's design of intersections that require no traffic lights

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7 pointscircusfly13 comments

That's essentially how the UK does motorway junctions. Lanes go to different places, road signs a few miles in advance and written in white on the lanes. Generally we don't bother with the U turn options as relatively few people want to go in the opposite direction.

If it looks like magic, your country is doing this wrong.

Benefits of said junction include noone needing to slow down. Drawbacks include some fraction of people accidentally going in a direction they didn't want, using quite a lot of land, general construction cost.

It's a roundabout.

I don't think so. Different fairness properties.

A roundabout has conventions for who has priority on enter/exit which means one of the lanes waits for a space in the other.

Motorway junctions and this example have the joining lane separate from the existing one so either can block the other.

Note that high traffic roundabouts usually end up with traffic lights to force a degree of fairness, where relative flow rate can be adjusted by different timing on the lights.

It's the difference between enforcing mutual exclusion by control flow vs a futex.

All I'm gonna say is if you reduce and optimize this design, you will end up with a round about.

But this one is much better if you really love u-turns

Yeah it seems like basically a hybrid of a roundabout and a Michigan left, with unclear advantages over either of those alone?

I read an article recently that said that left turns are terrible for traffic. One of the best ways to improve traffic is to ban left turns all together.

Doesn't it have an advantage over roundabouts in that the main traffic can keep moving at normal speed?

In practice you're going to get vehicles wanting to change lanes. Merging from both sides of a road at once is a terrible idea.

It's a roundabout with an unusual shape. Saved you a click.

Without the enter/exit rules, so any reasonable amount of traffic is going to cause many bottlenecks with merging and increased potential of accidents.

Migrating to this no stop merging scheme seems like it would be safer than changing all intersections from traffic lights to roundabouts where the majority of the population (e.g. America) has never seen a roundabout.

You may be right, having seen firsthand drivers almost launching themselves over a roundabout by not slowing down in both the USA & Canada.

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