What’s the deal with these variable speed limits through the northbound roadworks?
Travelled up that way about 3am for first time in ages.Gantry signs showed 40 which I religously followed. Though no evidence of any maintenance crews and hardly any traffic. Then towards end the overhead gantry shows 40 which I’m still doing and then I can read that the one further up says 20!! (20?) and can even see the next gantry sign further along says 40.(all three were in close proximity of each other)
Didn’t slow to 20 and neither did truck behind, seemed ridiculous…
Can only assume it was a mistake or is it some devious scam?
I don’t understand them either… I have to admit that during both rush hours they work quite well. However, they’re never illuminated early enough and remain lit long after they’re needed.
Nevertheless, late at night and the early hours of the morning, and as migs69 quite rightly remarks, they’re displaying ridiculously low speeds whilst nothing is going on. I reckon it’s some geezer sitting in the control room, bored, playing with the speed limits watching what everyone does on camera!
I wish they would leave those signs off for a month just to see what happens because the over use of these signs at the moment isn’t helping at all.
The point of reducing the speed is to help reduce speed to traffic so that when you get to the works your not all bunched up and stop start.
I have never had to stop as it alows traffic to keep rolling.
so answer this have you had to stop at night when going through the works at night ■■
If the answer is yes it’s because of traffic not slowing and trying to beat others.
The only bit that shows 20 is where traffic are merging form junctions and then its only in the one lane.
If your answer is no you havent actually stoped and traffic is still moving then it works
ROG:
Does THIS RECENT M42 THREAD help
I was looking for that thread rog. Had seen it before but couldn’t find it, hence the new post. 
thanks.
I was s/b on the M42 at 03.30 this morning.Joining it from 4A on the M6,the overhead matrix indicated a speed limit of 40 in lane 1 with a red X with flashing reds over lanes 2 and 3,with the warning,“Road works”.
At 2 places,the speed limit went from 40 down to 30 then back up again.
Despite the warnings over lanes 2 and 3,a Transit van was running side by side with an artic,but,getting fed up with seeing no road works,several cars moved into lane 3 and disappeared at 60 or 70 mph!
In the event,there were no road works to be seen.Had they finished?Had they even started?
The question is,do the cameras operate on lanes with the red X on?,I saw no flashes as the cars sped through.
bestbooties:
The question is,do the cameras operate on lanes with the red X on?,I saw no flashes as the cars sped through.
Motorway Gantry Cameras
There are currently two different Gantry Camera systems approved for use in the UK. The first is the old ‘wet-film’ GATSO system (as used on the M25), and the second is the new Highways Agency Digital Enforcement Camera System; HADECS system (as used on the M42).
How they Work
Both systems are used to enforce variable speed limits that are set by the highways agency on sections of motorway.A variable speed limit is a temporary, compulsory limit set to ease traffic congestion or slow traffic when there have been motorway accidents. They are imposed using electronic signs mounted on motorway gantries, and are denoted by the speed limit with a red circle the maximum speed.
Both systems use multiple cameras (one for each lane) mounted at the rear of the gantry usually behind the variable speed limit sign. They use radar for speed detection, and photograph offending vehicles from behind as they pass under and away from the gantry. Gantry Cams are unique in their ability to change their speed threshold automatically, so they match the imposed speed limit and only photograph vehicles exceeding the limit. The cameras are almost impossible for the driver to see and are highly effective at catching speeding motorists.