Flashing Traffic Lights to make them change
Discussion
How many times have you heard this one?
The lights controlling roadworks will change to green if you flash them with your headlights, 'cos the thing on top senses that.
Anyone else heard of some other modern classics oh and just as a sideline I found this site while seaching http://www.iusedtobelieve.com/transport/traffic_lights/
The lights controlling roadworks will change to green if you flash them with your headlights, 'cos the thing on top senses that.
Anyone else heard of some other modern classics oh and just as a sideline I found this site while seaching http://www.iusedtobelieve.com/transport/traffic_lights/
Don't know about the UK but in Dublin alot of the traffic lights have the sensors in the ground a couple of meters before the stop line. Hit the brakes hard as you go over them, thus loading up the front wheels, and they change green much quicker. Theres a set three doors down from my house and it works a treat all the time.
the sensors on top are essentially radar - they sense movement using the Doppler effect (no they can't measure speed!) and place a demand for the controller to change the lights or extend the green.
the sensors in the road are inductive loops - they sense a metal mass moving over them, and again change the lights.
Either system is type approved and they can be used separately or together at any junction.
the sensors in the road are inductive loops - they sense a metal mass moving over them, and again change the lights.
Either system is type approved and they can be used separately or together at any junction.
up-the-dubs said:
Don't know about the UK but in Dublin alot of the traffic lights have the sensors in the ground a couple of meters before the stop line. Hit the brakes hard as you go over them, thus loading up the front wheels, and they change green much quicker. Theres a set three doors down from my house and it works a treat all the time.
No they don't - speed makes no difference - there's either a vehicle there or there isn't.
up-the-dubs said:
Don't know about the UK but in Dublin alot of the traffic lights have the sensors in the ground a couple of meters before the stop line. Hit the brakes hard as you go over them, thus loading up the front wheels, and they change green much quicker. Theres a set three doors down from my house and it works a treat all the time.
LOL they used to have them years ago little strips run across the lane approx 15 feet from the lights I remember my dad used to do that through London, the first time it didn't work for him was with my Grandfather in the car with him
he got a right 
I think that the "flashing headlights" trick only works when the pressure sensors have not been already triggered by a vehicle at the other side of the lights. In Farnborough there are a couple of one-way light systems in use to allow cars to pass through narrow railway arches which can be triggered by headlamp flashing - but only when there are no other cars approaching or waiting on the other side of the bridge.
Flashing headlights does not make any difference! I'll say it again - the detectors sense movement, they are totaly insensitive to light - incidentally most of the "headlamps flasher" brigade who have set out to "prove" it, flash almost exactly at the point where the detector picks them up anyway - but this seems to keep them happy that they are right, bless them...
tvrgit said:
Don't know about the UK but in Dublin alot of the traffic lights have the sensors in the ground a couple of meters before the stop line. Hit the brakes hard as you go over them, thus loading up the front wheels, and they change green much quicker. Theres a set three doors down from my house and it works a treat all the time.
No they don't - speed makes no difference - there's either a vehicle there or there isn't.
Not the ones near me. The lights change pronto for a bus (within 10 seconds) whereas a car might be there for a minute. Hitting the brakes, shifting the weight on to the front, trips off the sensors. You seem to know how these systems work so I won't argue the point, but thats how it seems to work here.
I didn't mention speed at all?
up-the-dubs said:
Not the ones near me. The lights change pronto for a bus (within 10 seconds) whereas a car might be there for a minute. Hitting the brakes, shifting the weight on to the front, trips off the sensors. You seem to know how these systems work so I won't argue the point, but thats how it seems to work here.
Ah - selective vehicle detection to give bus priority - that's a separate detector from the usual "car and lorry" ones. They are usually set to respond to transponders on the buses (active selection) but can also be loops "tuned" to recognise a particular vehicle profile passing over (passive selection) - for example a vehicle 10 metres long, very low chassis with light body, and enormous mass of engine at back = "bus", anything else = "not a bus". I suppose it *might* be possible to fool them by doing a certain manouevre if they weren't "tuned" properly... maybe.
Normal "car" detectors will not be influenced by speed (by that I meant how the car moves over the loop) - there is either a mass of metal there, or there isn't.
tvrgit said:
Ah - selective vehicle detection to give bus priority - that's a separate detector from the usual "car and lorry" ones. They are usually set to respond to transponders on the buses (active selection) but can also be loops "tuned" to recognise a particular vehicle profile passing over (passive selection) - for example a vehicle 10 metres long, very low chassis with light body, and enormous mass of engine at back = "bus", anything else = "not a bus". I suppose it *might* be possible to fool them by doing a certain manouevre if they weren't "tuned" properly... maybe.
Normal "car" detectors will not be influenced by speed (by that I meant how the car moves over the loop) - there is either a mass of metal there, or there isn't.
That sounds about right. I remember they trialled a bus sensor thingy (very technical term that) that would change lights quick for the buses. I've never heard what happened to it or if they changed it for the road sensor thingys or if it's there at all now. But thanks for the reasonable response. I was afraid of abuse
. You do sound like you know what your talking about.
Perhaps you could have a coded flash lasting say 100ms. I understand that aircraft have this on their beacon lights (or am I wrong)Gassing Station | The Pie & Piston Archive | Top of Page | What's New | My Stuff