M1 Speed Cameras near Hemel Hempstead

[GuitarPlayer63]

Does anyone know what speed actually triggers these cameras to flash? They're located over every lane on the M1 at J8 (Hemel Hempstead) north and southbound. I've seen them flash many times in front of me on the other carriageway and behind me when I was doing about 65 and nobody else was going any faster beside me which makes no real sense.

I can't work out if there is a predetermined limit they flash at, or if it's simply randomly to get people to pay attention.

[GuitarPlayer63]

be careful, there is a growing use of Average Speed cameras on motorways, so I can only guess the "Warp 1 approach" will be rumbled (damn!) and there are no signs to say they are measuring average speed.