Rob K:
trevHCS:
Side ones are easiest to spot by lookong out gor the cameras just before them, usually a bank of 3. No idea what they do but always seem to accompany these yellow side cameras.They also need to turn down the flash on the side ones or angle it better as its way too bright at night for the traffic on the other carriageway. Gave me a shock in truck other day when speeding car passed me and there was a flash behind me (I was doing 50 with no temp limit).
Wouldnt rely on the above lane ones not working on the M1 - seen them flash a few times in past couple of years when temp limits are on, but not always.
The 3 cams about 200 yards before them are synchronised with the cameras that nab you for speeding. They take a photo of the gantry and the speed limit displayed so that you can’t argue it was displaying a different limit. There is (iirc) a 30 second delay from when a temporary limit is first displayed until the speed enforcement commences. I read it somewhere in the camera system specs I found online - possibly Siemens but could be mistaken, but there is a delay before they start enforcing the limit, I know that much.
The 3 cameras are there primarily to show that the matrix is readable. On previous systems if so little as one bulb in the matrix failed the system automatically defaulted to no enforcement. Now lots of bulbs can fail so long as the sign is still shown to be readable and the till keeps getting fed.