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Flashing your headlights at temporary traffic lights

Lisa Miles

I'd like some of our engineers working in the Automotive and road transport systems industry to settle an argument I've been having with my partner for some time now. 

He's convinced that flashing your headlights at the temporary traffic lights you see controlling traffic flow at roadworks causes them to turn green. Now I understand his thought process in that there are sensors there that will 'see' there's vehicles waiting but I don't think that flashing your headlights makes any difference at all? 

For example one evening last week (it was still daylight) we were out and about and while driving through a local village we came across some roadworks. As we approached the temporary lights you could see that there were no cars waiting on the other side so he starts flashing our headlights and in a few seconds the lights turn green. Now he's convinced that they turned green because he was flashing the headlights whereas I pointed out that 30 seconds before there were two cars travelling in the opposite direction from us that would have just gone through the lights. The fact that they turned green when we got there was purely because we had hit the sequence at the right moment. He on the other hand is convinced that flashing your headlights at them will turn them green if there are no other cars coming through. 

So what is the answer? Does it or does it not? Thinking

Parents

  • For example one evening last week (it was still daylight) we were out and about and while driving through a local village we came across some roadworks. As we approached the temporary lights you could see that there were no cars waiting on the other side so he starts flashing our headlights and in a few seconds the lights turn green.

    I've seen similar symptoms, but the cause is I suspect different. In some of the semi-rural areas around here you can see lights that settle on all-red when there's no traffic about, and then change to green for approaching traffic pretty much as it arrives - but triggered I'm sure by the Doppler system that Mike described.  It would be an interesting to repeat your partner's experiment, under the exact same conditions, but without flashing headlights and see if the change the same anyway - I suspect they would.

      - Andy.

Reply

  • For example one evening last week (it was still daylight) we were out and about and while driving through a local village we came across some roadworks. As we approached the temporary lights you could see that there were no cars waiting on the other side so he starts flashing our headlights and in a few seconds the lights turn green.

    I've seen similar symptoms, but the cause is I suspect different. In some of the semi-rural areas around here you can see lights that settle on all-red when there's no traffic about, and then change to green for approaching traffic pretty much as it arrives - but triggered I'm sure by the Doppler system that Mike described.  It would be an interesting to repeat your partner's experiment, under the exact same conditions, but without flashing headlights and see if the change the same anyway - I suspect they would.

      - Andy.

Children
  • in reply to AJJewsbury

    In fact I wouldn't be surprised if it appears to work quite often, as it's quite likely that due to the time before the driver gets bored and starts flashing their lights is very similar to the time interval chosen for the crossing change (because it needs to be short enough to not cause an impatient driver to jump the lights).

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