On Monday, September 5, 2016 at 8:36:44 PM UTC+1, charles wrote:
In article ,
misterroy wrote:
On my way to work a bridge is being repaired. Today I was in the stream
of traffic heading towards town, no cars going the other way. Mid stream
the lights went red, just as I reached them. I went through. I reckon I
travelled 100m between the lights and then about 600m up the hill before
the lights changed. I realise there has to be a margin to be sure a car
gets through, but how big should the margin be? Why when the lights have
sensors do they never seem to be switched on? It just looks like a crude
timer is used. Under what circumstances are the sensors on the lights
used?

For at least the last 30 years, the use of sensors has been mandatory.

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from KT24 in Surrey, England
I think the traffic lights here are just set on a timer and the sensors not used, and the timer is always way way longer than is needed to clear the lights.
So if I am approaching a set of these lights at red, and I am the only car on the road, how long should it take for them to show me a green?