traffic lights at roadworks.

[misterroy]

On my way to work a bridge is being repaired. Today I was in the stream of traffic heading towards town, no cars going the other way. Mid stream the l ights went red, just as I reached them. I went through. I reckon I travelle d 100m between the lights and then about 600m up the hill before the lights changed. I realise there has to be a margin to be sure a car gets through, but how b ig should the margin be? Why when the lights have sensors do they never seem to be switched on? It j ust looks like a crude timer is used. Under what circumstances are the sensors on the lights used?

[Nightjar]

Modern temporary traffic lights always use traffic sensors. However, they also have a maximum length of red signal, which varies from 2-5 minutes, depending upon normal traffic flow on the road. When that maximum is reached, the lights will change, even if no traffic has been detected from that direction and there is still traffic coming from the opposite direction. It is a precaution against sensor failure leaving one direction permanently stopped. The time before the lights change red in one direction and green in the opposite direction depends upon traffic flow, speed limit through the works and the length of the works.

Contrary to urban legend, temporary traffic lights are compulsory lights and passing the 'If Red Light Shows Wait Here' sign, or the lights if there is no sign, when the red light is showing is an offence.

[James Wilkinson]

That doesn't explain why the OP's light didn't switch back until 600m after he'd passed the other end. No traffic the other way means it must have gone red for him on the timer. But it should have changed back after the minimum get through time as there was traffic waiting behind the OP.

Except if you're in a queue of traffic, there's no harm in following the car in front. It would also be stupid to stop if you'd moved over to the right to follow the queue, but passed the sign when they went red.

[damduck-egg]

ISTR that at one time when they only exhibited a red and green that wasn't the case then temporary traffic lights adopted the three lamp Red Green Amber combinations so that they could be made compulsory. The urban legend probably stems from the two lamp era, which leads to wonder what if any offence may be commited if you ignore the geezer with a Stop /Go board when he turns it to stop as you approach.

G.Harman

[Scott]

Can traffic sensors always detect cycles?

[ARW]

I guess they could if the aimed them onto the pavements.

[charles]

For at least the last 30 years, the use of sensors has been mandatory.

[Clive George]

Recent ones have IME.

[Robin]

assuming they are properly authorised geezers, the same offence as ignoring a red light. And some of those Stop/Go boards are fitted with video cameras to provide evidence.

that is of course quite separate from the possible offence of pissing of the geezer's mates down the road who happen to have readily at hand plenty of stones, shovels, dumper trucks, etc

[misterroy]

I think the traffic lights here are just set on a timer and the sensors not used, and the timer is always way way longer than is needed to clear the lights. So if I am approaching a set of these lights at red, and I am the only car on the road, how long should it take for them to show me a green?

[misterroy]

Found this on a govt site "Vehicle Actuation (VA) All equipment used on public roads must be capable of working in Vehicle Actuated (VA) mode. These signals use detectors to monitor traffic flows and use this information to adjust the length of the signal green time to reduce delays. VA mode should always be used unless there is a specific reason, such as using the manual mode on a short-term basis to move plant into, or out of, the controlled area. Use of VA will help to reduce unnecessary delays. If the signals are to be operated under manual control at any time, both ends of the working area should be clearly visible to the operator at all times. Vehicle detectors (Microwave Vehicle Detectors, or MVDs) used at portable traffic signals must have received type approval from the Highways Agency. To be able to work in the VA mode it is essential that the MVDs are set up as detailed in the Pink Book1 ."

from

[charles]

Temporary lights have switch for setting the distance between the two ends. Perhasp this has been wrongly set because those who set them up don't know the real distance and have set it to maximum.

[The Natural Philosopher]

The bloody lights themselves are an offence.

[Harry Bloomfield]

It happens that misterroy formulated :

Long enough for the lights at the far end to change to red, plus what ever time it might take a slow vehicle to make it through and clear to your end. It might be much longer, where the lights include a junction and an extra road.

[dazlewis1970]

A factor of six allows for pushbikes going at one sixth the speed of your car.

[Bill Wright]

During my brief career as a traffic liaison officer (stop go man) we would note the time when a car ignored a red and the next morning look out for him, then jump out and hold him up for ages. We also put bricks inside a few of the roadcones to piss off the truckers who used to take out a row of cones just for fun.

Bill

[Nightjar]

My car radar does and they use radar sensors to detect pedestrians waiting at or crossing at lights controlled crossings, so I would think they should. However, even if they don't, the maximum red cycle setting will ensure that the lights change anyway.

[Nightjar]

Exactly so. Only two light temporary lights with the word POLICE between the two lights (and usually on the stand) were compulsory. They were taken to be an instruction to stop given by a police officer.

Same as passing a red traffic light.

[Nightjar]

It depends upon how fast he was going. At 60mph it would have taken him less than 30 seconds to cover the distance.

Neither would provide you with a defence in Court.

[James Wilkinson]

Didn't you know, you're supposed to drive fast through a red to minimize the chances of hitting something else.

Clearly you check for pigs first. Anyway, it's no worse than speeding is it?