Red light camera....red/Amber ?

almillar

When the light goes green, why doesn't the entire queue move off as one? In principle, there's no reason why not (assuming everyone can see the green light).

Absolutely. The reason, of course, is that even if the 1st person in the queue IS paying attention, the second person probably isn't, so you've got cars stopped at a green light with nothing in front of them, contributing to traffic jams.

DoaM

This reminds me of the old QI question ... What travels the wrong way along a motorway at 12mph?

Brake lights, or a phantom traffic jam. This is caused when one car suddenly slows down, then it speeds up again. The car behind it will also slow down, and speed up again. This ripple effect travels downwards causing more cars to slow down until eventually they jam up.

JP08

almillar wrote: »

Absolutely. The reason, of course, is that even if the 1st person in the queue IS paying attention, the second person probably isn't, so you've got cars stopped at a green light with nothing in front of them, contributing to traffic jams.

But even if you did all move at once you wouldn't all go at the same speed unless driving recklessly. If you've got to leave a gap between you and the car in front to brake safely if they suddenly stop (as you should), that gap will have to get bigger as you go quicker. So you can't go as fast as the car in front, and the car behind you can't go as fast as you. And so on down the queue.

almillar

But even if you did all move at once you wouldn't all go at the same speed unless driving recklessly. If you've got to leave a gap between you and the car in front to brake safely if they suddenly stop (as you should), that gap will have to get bigger as you go quicker. So you can't go as fast as the car in front, and the car behind you can't go as fast as you. And so on down the queue.

Yes. Yes! But what you're describing is a queue of drivers all sitting, paying attention, all looking at the lights, amber comes on, they all go into gear, green comes on, they all go. I've never encountered a queue that's anywhere NEAR that switched on, and there's always someone picking their nose, checking their phone, talking to a passenger etc, that leaves an UNREASONABLE GAP that other cars could have been in.