Motorway variable speed question

No it is not correct.

If there are no repeater 50mph signs after the first 50mpg sign the speed limit is 70mph even though you may have slowed to 50mph to pass through the first sign. If all the following electronic overhead gantries display the 50mph maximum speed limit sign then the speed limit applicable is 50mph (because the overhead electronic gantries are usually no more than 500 metres apart) The default speed on a motorway (for cars) is 70mph. I believe Highways (England) have perhaps been disingenuous here because they hope they can get vehicles to slow down (for something?) But it doesn't say what for even though the sign may be of the prescribed size etc. The other possibility is that the automatic cancellation on this particular temporary speed limit sign has failed.

In order to be lawful the mandatory speed limit signs should be of a certain diameter. (50 mph should be 1200mm) There should be additional repeater 50mph signs also of a prescribed distance (& size) 250m after the first 50mph sign, and then at regular intervals no greater than 500metres apart. So if after this first 50mph sign there are no other 50mph signs the speed limit applicable to the Motorway is 70mph.

The set of legislation that covers this is: The Traffic Signs Regulations and General Directions 2002 (TSRGD) The Department of Transport also provides Local Authorities with 'guidance' in the placing of such speed signs in The Traffic Signs Manual (TSM) There are a great many caveats and some is guidance. Highways (England) and Transport Scotland operate their own justifications for temporary speed limits on Motorways.

You would have to challenge the legality of the fairness of repeater signs in court if they were absent or not visible (ie challenge your fixed penalty notice) but the difficulty starts when you have no control over the electronic signs (you have to rely on Highways evidence that they were operative) The only counter measure is dash cam evidence. Temporary speed limits at roadworks need additional 'orders' to make a lower speed limit valid, on single carriageway roads or motorways. Highways do not need to keep applying for 'orders' on smart motorways for certain obstructions, safety or pollution

The practicalities of re-visiting a Motorway section to measure distances by car of placed temporary metal signs or the distances between electronic operative signs (these site placements will be static and standard) is dangerous and virtually impossible. The trick is to notice where the preceding spotter cameras are and then where the actual ANPR registering speed cameras are. These are usually a few hundred meters apart, and mounted on the hard shoulder side of an overhead gantry. Old style cameras are mounted on some of the overhead sections of gantries above each lane. Some are static speed measuring cameras, others are average speed cameras.

I agree with you, there is not enough information for ordinary motorists about the wealth of electronic speed limit signs and additional information about enforcement here.