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I don't go to the south east very often. In fact I try to avoid it at all costs, however no such luck yesterday as I had to make a trip to Essex.

Anyway in the roadworks on the M25 they've put up a very expensive looking gantry with traffic lights on it, a separate set for each lane and two either side for good measure. It doesn't look like a temporary arrangement. There's a similar set when you come back the other way.

Please tell me this is just for the roadworks and not a permanent installation as that is going to cause so many accidents if it is ever used.


(in a related note, when coming home the opposite direction was shut because a Prius had chosen to drive into the back of a Sprinter van. I hope the Prius driver realises that the massive stationary tailback he caused, plus the related almost stationary tailback on the opposite side will have put out more CO2 in one traffic jam than that Prius has saved thanks to it's hybridness)

Yes, it is something to do with the roadworks only.

Basically to prevent vehicles sitting in stationary queues in the tunnel and gassing the drivers/workers.

Made me think when I saw them about a month ago!

Sort of related question.

What is the purpose of putting traffic lights halfway down the slip roads onto motorways? I've seen them at J8 and J6 on the M25 and also J3 on the M3.

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It's called "ramp metering". The theory is that the lights can be used to keep traffic flowing on the main motorway by restricting the amount of vehicles joining from the slip road. In practice, of course, all it's doing is shifting congestion back on to the local road network. It's fairly widespread now in the North-West on the M60 and M6.

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"Show me someone who says that they have never exceeded a speed limit, and I'll show you a liar, or a menace." (Austin Williams - Director, Transport Research Group)

Any views expressed in this post are personal opinions and may not represent the views of Safe Speed

It seems that they are becoming common on all motorway slip roads. I mentioned them to a friend at work and he said the M4 now has them

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