In the majority of cases, the camera is mounted in the rear as the camera is usually on a tripod to be operated by someone standing upright, hence the fact that most camera vans are high roof Vauxhall Movano type vehicles. I can see the time in the not too distant future when they just park the van up
and the camera does all the work like a gatso, in which case they can have them anywhere on the vehicle including the roof. With that in mind, I seem to remember a story, possibly apochryphal, of a Copper checking vehicle speeds,
possibly in Scotland, who being bored, pointed his radar gun at a low flying Tornado attack aircraft which was heading out over the North Sea to carry out a live firing exercise to see if it would show the plane's speed. The R.A.F. later informed his Inspector that the aircraft's electronic suite had armed the Paveway 1000 lbs. bomb and was giving the pilot the co-ordinates to attack the threat. That's one way to get rid of speed cameras.