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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

  • 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.

  • in reply to mapj1

    Hello Mike:

    Having driven multiple million miles on US roads I have never seen a "stand alone" relocatable 3 lamp traffic signal lamp like you have in the UK.

    I have seen "odd ball" permanent signal lights like ones with only two lights (missing yellow) or where the red light is at the bottom and green up on the top .

    Peter Brooks

  • in reply to Andy Millar

    having worked on the electroncs of the sensors for traffic lights and crossings...

    Mostly they are microwave doppler based - so if you approach very slowly you will be missed. There is no magical over-ride by light sensors, though some can be programmed by vhf radio, and others have a sim card and can be sent a text message, as can some of the digital roadworks signs. The Doppler sensors sense in both directions, so know when things going the other way have passed and it is safe to change the lights.
    There are some that use an infra red lidar type arrangement but again no flashing lights over-ride.

    Static lights often use metal detectors in the road, loops of wire facing up looking for the change in inductance. These often miss things that are not cars - bikes, traps, horses etc. and one can make (ssh, legality uncertain..) things that receive the metal detector signal and create a giant emulated target. " for educational purposes"

    Mike.

  • https://optraffic.com/blog/headlights-and-temporary-traffic-signals-myth/#:~:text=Experts%20agree%20that%20the%20myth,of%20which%20include%20flashing%20lights.

    I particularly like (it's a US site):

    Such events contribute to the myth’s endurance, even spreading to places like Britain in 2004.

    So I think that's a no then! It's a good myth because it suggests that the person who's telling it has a secret power, and the fact it doesn't work for us is only because we didn't flash them quite the right way...you can only disprove it by actually being in a car with the person who's saying they can do it and happen to come to a set of temporary traffic lights...and even then I'd bet it'll be "oh, my mate in the police told me that it doesn't work with this type"! Laughing

    My experience with emergency services is also that they will tend to just plough through anyway, I can't imagine them waiting for some dodgy electronics to respond to a particular light flash.  

    Traffic myths always remind me of someone I worked with years and years ago who was a part time motorbike instructor who proudly told us that if we were ever stopped for speeding we could always get out of it by saying we were "making maximum safe progress". I'm afraid we found it somewhat satisfying that he was stopped and successfully fined for speeding only a couple of weeks later...

  • in reply to Sergio Fernandez

    I remember a short while ago reading something about the emergency services in the USA having an infra red light or something that broadcasts out to a sensor on their lights to change them so they can continue unimpeded. But as far as I know (and I'm sure someone will correct me if I'm wrong) we don't have that in the UK as I've seen countless police, ambulance and fire engines go through red lights anyway! 


  • I remember many years ago now I was told the same (possibly decades ago).  Flash lights on approach to temporary traffic lights and it make the light turn Green.  The concept was that an emergency services vehicle approaching with flashing front headlights get given the priority.

    As a side note might be worth looking at Highway Code rule 110 and 111 I think

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