traffic light sensors

[sophie_1003]

Do traffic lights detect that cars are there by a sensor that detects headlights? This is due to an argument between me and my peers at uni and one of our tutors who says that the only sensors that traffic lights have are a pressure pad in the road so any links proving otherwise would be lovely!

[sophie_1003]

ok everyone, thanks for clearing that up! am disappointed about being wrong though :(

[kent18]

if you though traffic lights worked on detecting head light.ask yourself what when its daytime and none if not many peole have head lights on.And you are at uni,god help us.Sensors in the road.is correct.

[sophie_1003]

no, hadn't really thought about it in too much detail but if had to come up with a theory I would have said that they detect the movement of the car and so if you flash your lights it seems like the car is closer. Or something like that. Anyway, what I'm studying at uni has nothing or at least, very little, to do with how sensors work so even if i had no thoughts on it at all it wouldnt really have an influence on the fact that im at uni in the first place.

[matrix2021]

Well thank god for sddsddean's input, because I'm sick of having continuous arguments with taxi drivers (and some dumb friends) that believe flashing their headlights at traffic lights changes them more quickly. One determining factor that goes against me EVERYTIME, is the fact at 3am when your traveling down quiet roads and you encounter a red light, it changes almost immediately when the taxi drives over the 'ground sensor'/inductive loop - but they fail to realise that if there's no traffic on the other road then it WILL change almost suddenly.

What I would like to know though, is that on some older traffic lights (not the new LED ones) some do have a black looking sensor on the top - but also have the inductive loop on the floor... Is this a secondary measure?