Tuesday, May 8, 2012

Traffic lights - timer is useful but may be not for green light

Roy Sutherland gives an example of traffic lights in Perspective is Everything. In Korea, there is a timing indication on red light only and it works to reduce accidents. In China, there is timing indication on both red and green lights and it doesn't improve accident rate - it may even be worse.

Chandigarh uses the 'Chinese' model. I wonder if its effectiveness was ever tested.

It is pretty obvious that knowing how long one has to wait helps cope with waiting. Uncertainty is disturbing.

In the case of a green light, there are conflicting goals. If the traffic is light and a driver knows how long the green light will remain on, he may speed up to reach the junction before the signal changes. On the other hand, knowing that there is not enough time may help us to stop in time before the zebra crossing.

In the case of the green light, it would be enough and, probably, safer if we get information that the light is about to change and nothing more than that. This signal should be obvious.

So, it might be better to have the timer only for red signal. For green signal, it may be useful to have amber light on about 5 seconds or less before the green light goes off, letting the driver know that it is time to slow down and stop.

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