Flashing headlights at traffic lights

[elpea]

I was in a taxi recently which was stopped at a red light at a junction. The lights seemed slow to change, and the driver got impatient. Next thing I knew he'd slammed the taxi into reverse, reversed about 20 feet then flashed his headlights repeatedly at the traffic lights. I was bemused and asked what he was doing. He claimed some traffic lights have a sensor which is triggered by this flashing which will make the sequence change to green faster... I'm sceptical - do any ABers know about this? Is it true? I hope someone can help as none of my friends know about this!!

[chazza]

Some do and some don't.

The ones that do, have a sensor so that they can see how much traffic has built up in each direction and then changes accordingly. Flashing the lights makes them think that it is another car pulling up and makes them more likely to change.

The lights at the end of my road are like this and we get them to change everytime we pull up to them at night.

[agamad]

There are also sensors in the road. It you look at the road approaching traffic lights you may see an oblong rectangle cut into the road at an angle. There are usualy two of them as you approach. Going over these tells the lights someone is in the queue and having two will give some indication as to the length of the queue.

[RATTER15]

Its the motion of the car not the flashing lights.

[sddsddean]

Flashing your lights has absolutely no effect on the timing of the traffic lights. It also has no effect on temporary traffic lights either. The only types of detectors are either detector loops (cut into the road prior to the lights), or microwave detectors (the 4" square boxes mounted on top of the light head). Both these systems detect the presence of the vehicle; not the stream of photons from the headlights!!

[buildersmate]

I reckon Ratteris is close to the mark. I found out about this when I came to a set of TLs via a small sliproad emerging right on top of the lights, after these rectangular sensors. It was a quiet Sunday and I sat there for several minutes with nothing coming the other way before something came up behind me and the TLs changed. I have since found that one can often 'force' the lights to change quicker by sitting on the back sensor, irrespective of whether the sensors in front have cars sat on them. Works best in a side street entrance onto a main road. Nor recommended if someone comes up behind you - they don't realise you are playing cunning. Give it a try sometime.

[markja]

i had a simillar experiance at heathrow years ago,long before terrorists were invented. it was about 2;30 am and i wanted to turn right off the perimiter road ,i was on my motorbike.the sensor in the road hadn't picked up my bike passing over it. so i was stuck at the lights on red. i couldn't jump them 'cos a plod mobile was parked up very close by. i reversed the bike back a bit and wheeled it forward a couple of times before the sensor 'saw' me. as i rode off the plod pulled me 'cos i had acted strangely at the lights.
it took ages to get them to understand what had happened. probably had a good laugh in the station canteen later on.

[BillyBB]

There was a rumour that traffic lights had a sensor to detect the flashing headlights of a ambulance etc. I suspect this is urban myth, seeing as they are allowed to jump a red anyway.

[pagey]

buildersmate,

I have a set of lights near me where you pull forward from one set on green to the next (always red - right turn filtered lane). If I pull forward very slowly ~5mph the lights appear to change faster (regardless of oncoming traffic volume) than if I just pulled up to the line and waited. I think this may be the second induction loop sensing me for a prolonged time

[elpea]

thanks, I think I'll have to go with ZebUK due to the reference of setting up traffic lights! I was hoping someone who had worked with traffic lights would answer, as I've heard so many different versions of the 'truth' from various drivers, which I've been sceptical of.