Flashing lights at traffic light .

[ARHarh]

the road that goes past my house down the hill has roadworks on it. I was sitting having a cup of tea, watching the world drive by and at least 50% of the cars approaching the traffic lights flashed their headlights. Do they think this influences the behaviour of the lights or is there some other reason?

[TooMany2cvs]

ARHarh said:

the road that goes past my house down the hill has roadworks on it. I was sitting having a cup of tea, watching the world drive by and at least 50% of the cars approaching the traffic lights flashed their headlights. Do they think this influences the behaviour of the lights or is there some other reason?

You see the little sensor box above temporary traffic lights? The story goes that flashing that makes the lights change more quickly. I've heard tell that only the emergency services are meant to know, as an over-ride. I've heard various other theories. It's certainly a well-known story, whether it's true or not.

[normalbloke]

Not true, complete tosh. The eejits flashing their lights are just letting the world know how little they understand.

[Reg Local]

Partially true is my understanding - temporary lights are primarily controlled by a timer unit within the generator they're connected to, but at night they used to have a light sensor on top which recognised approaching headlights & controlled the lights accordingly.

These days I understand the box on top of the lights is a motion sensor and will recognise the movement of approaching vehicles irrespective of daylight.

The above may all be incorrect, but I've heard similar from a number of different reliable sources.

[jamei303]

Reg Local said:

Partially true is my understanding - temporary lights are primarily controlled by a timer unit within the generator they're connected to, but at night they used to have a light sensor on top which recognised approaching headlights & controlled the lights accordingly.

Why would they have a timer that worked perfectly well during the day but go to the trouble of fitting a second mechanism for operation at night? Why wouldn't they use the same system on fixed traffic lights? It's bks that's what it is.

[ging84]

it's a myth, but regardless even if it was true, not many people would be doing it, certainly not 50%, i suspect what was being observed was a bump in the road.

[pwd95]

Motion sensor. As your driving toward it, day or night you can see the little Red LED come on .......

[pincher]

Wasn't there an epic thread on this subject a few years ago? Someone was adamant that it was true and he was going to video it or some-such, and was quite heavily ridiculed for not coming up with the evidence?

Someone with better search powers can dig it out, I'm sure

[Reg Local]

jamei303 said:

Reg Local said:

Partially true is my understanding - temporary lights are primarily controlled by a timer unit within the generator they're connected to, but at night they used to have a light sensor on top which recognised approaching headlights & controlled the lights accordingly.

Why would they have a timer that worked perfectly well during the day but go to the trouble of fitting a second mechanism for operation at night? Why wouldn't they use the same system on fixed traffic lights? It's bks that's what it is.

This Department for Transport publication suggests that it is not, in fact, bks:

https://www.gov.uk/government/uploads/system/uploa...

[jamei303]

Reg Local said:

This Department for Transport publication suggests that it is not, in fact, bks:

https://www.gov.uk/government/uploads/system/uploa...

Where does that mention headlight detection

[Evanivitch]

I always thought the boxes on temporary lights were to detect strobe lights from emergency vehicles, hence why people tried to flash their lights to change them. Turns out that was wrong

[mwstewart]

jamei303 said:

Reg Local said:

Partially true is my understanding - temporary lights are primarily controlled by a timer unit within the generator they're connected to, but at night they used to have a light sensor on top which recognised approaching headlights & controlled the lights accordingly.

Why would they have a timer that worked perfectly well during the day but go to the trouble of fitting a second mechanism for operation at night? Why wouldn't they use the same system on fixed traffic lights? It's bks that's what it is.

Because generally there's less traffic at night ergo 'on demand' switching is a far better solution.

[marmitemania]

Not this again! We have had several sets of temporary traffic lights on a road I use regularly, I have approached the lights several times in the dark as they are turning red or have just turned red, a flash of the headlights see's them going straight back to green, so either there is a motion sensor/light sensor or it's fking witchcraft. Fixed lights have vehicle detection systems so why should temporary lights not have this function? All be it working in a different way to the magnetic loops used in the fixed lights.

[Higgs boson]

Complete myth.
The sensor is not always used. In the vast majority of cases it should be set to vehicle detection.
There are different modes in which the lights can be used ...
All red, manual, fixed time, and vehicle detection (can be called vehicle actuation, or vehicle activation).

[Willy Nilly]

pincher said:

Wasn't there an epic thread on this subject a few years ago? Someone was adamant that it was true and he was going to video it or some-such, and was quite heavily ridiculed for not coming up with the evidence?

Someone with better search powers can dig it out, I'm sure

There was a thread on which featured it, urban myths or something. Someone who was a traffic light engineer even photo'd the inside of a set of traffic lights, but the poster was adamant, though never returned with their findings.

[marmitemania]

Higgs boson said:

Complete myth.
The sensor is not always used. In the vast majority of cases it should be set to vehicle detection.
There are different modes in which the lights can be used ...
All red, manual, fixed time, and vehicle detection (can be called vehicle actuation, or vehicle activation).

How can it be a complete myth if the lights have a vehicle detection mode? I think I may have been seeing things when I passed through the lights twice a day in the dark for months on end.

[motco]

Vehicle detection is a microwave Doppler movement sensor. It is unaffected by light and responds to a Doppler shift in the reflected signal from an approaching vehicle.

[ging84]

jamei303 said:

Reg Local said:

This Department for Transport publication suggests that it is not, in fact, bks:

https://www.gov.uk/government/uploads/system/uploa...

Where does that mention headlight detection

It mentions Microwave Vehicle Detectors,
Lights, microwaves, they're basically the same thing right ?

[Willy Nilly]

here you go : http://www.pistonheads.com/gassing/topic.asp?h=0&a...

[Reg Local]

ging84 said:

jamei303 said:

Reg Local said:

This Department for Transport publication suggests that it is not, in fact, bks:

https://www.gov.uk/government/uploads/system/uploa...

Where does that mention headlight detection

It mentions Microwave Vehicle Detectors,
Lights, microwaves, they're basically the same thing right ?

I'm pretty sure I said they were motion detectors in my original, unedited post.

Reg Local said:

Partially true is my understanding - temporary lights are primarily controlled by a timer unit within the generator they're connected to, but at night they used to have a light sensor on top which recognised approaching headlights & controlled the lights accordingly.

These days I understand the box on top of the lights is a motion sensor and will recognise the movement of approaching vehicles irrespective of daylight.

The above may all be incorrect, but I've heard similar from a number of different reliable sources.

Yep. Thought so.