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Is there any city in the world with well-timed traffic lights over a large grid?

I just want to usually hit 10 green lights in a row when going above 40 mph for all 4 directions (during peak traffic time).

It doesn't seem like it would be that difficult (I would start by outlawing left turns), but I'm always frustrated in California. So, where do city engineers do better? I think the government underappreciates the morale/environmental/time benefits of reducing traffic jams.

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    How do you drive in four directions at once? – phoog Jul 7 '18 at 13:15
  • @phoog You have 4 drivers to check the grid (or 1 driver tests sequentially that all 4 directions work) if you really need an exact experiment. I thought you were making a joke, but then somebody up-voted your comment, so responding seriously. – bobuhito Jul 7 '18 at 18:20
  • Well it was a somewhat facetious way of putting it, but I was seriously curious about what you meant. It's not possible to time the lights in four directions on an urban scale. – phoog Jul 7 '18 at 19:00
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It's called a Green Wave. Co-ordinating it on two-way streets with varying distances between the junctions is tricky.

  • I'd rather call it "coordinated green waves in all 4 directions". Can you add a particular city where you think it's done well? – bobuhito Jul 7 '18 at 13:09
  • I don't believe you can have all four dimensions simultaneously. It's fundamentally not possible. – Someone Somewhere Sep 30 '18 at 5:52
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Well, I'm not sure there's a ranking anywhere, but Manhattan would seem to do pretty well, and there's evidence to back it up.

NY Daily News reported that an uber driver hit a 'record' 240 green lights in a row driving in Manhattan, and recorded the event as well.

  • Thanks, and good reference. I'd guess these streets have a 30 mph limit, so I'm still looking for something faster... – bobuhito Jul 7 '18 at 13:18
  • Streets with 40mph limits are effectively small highways, and urban areas don't have large grids of 40mph streets, because that would be horribly unsafe. Since traffic congestion increases to match the capacity of roads, it's near impossible to have sustain this for long during peak traffic time, as traffic jams will soon slow things down to the point where you're missing lights again. – Zach Lipton Jul 7 '18 at 22:48
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It is mathematically impossible to do even for both directions at once, as you cannot control the distances between traffic lights: the 'green waves' need to travel with you, at the same speed, and at the same time the ones for the opposite direction needs to travel too, but in the opposite direction. They simply will not hit each other exactly at all crossings, which makes it useless. Unless you want all cross traffic to stop for ten minutes.

  • I wish we hadn't started with the word "wave" because that is misleading. You can go both directions if the frequency for the light switching is exactly the time it takes to drive from light to light at 40 mph. – bobuhito Jul 7 '18 at 18:15
  • @bobuhito that's impossible at urban scales. – phoog Jul 7 '18 at 19:02
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    It might work in some cities which have standard size blocks, (like some in the USA.) In most of the world you will find the blocks less equal in size. – Willeke Jul 7 '18 at 20:22
  • If you do the math, and assume one minute green and one minute red, the traffic lights need to be ~1.5 miles apart for that to work. I don't know any city with traffic light that far apart. – Aganju Jul 7 '18 at 20:28
  • So, do 10 seconds green, 10 seconds red, and it's reasonable. Please don't give up so easily. – bobuhito Jul 7 '18 at 22:32

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