I thought entire point of these was that you got a speed limit warning for the first gantry, then it was enforced at the next one? Otherwise how are you supposed to react if you are less than 100m away and it changes?
If this the cause of a load of people slamming on their brakes on motorway, then this is a crazy situation, and ludicrous.
If this the cause of a load of people slamming on their brakes on motorway, then this is a crazy situation, and ludicrous.