I think I delivered my version of roads justice failry and evenly over the time I applied it, be that the guy in his new Porche doing well on the wrong side of a ton at 4am on a deserted motorway getting a warning as well as the guy in his new Porche doing 40 in a 30 outside a playground getting booked as there were kids running about and chasing footballs onto the roadway.
Same fella, as it turns out, with the incidents 2 years apart. He appreciated my viewpoint on both stops and graciously accepted the justice dealt out.
Speed camers (the fixed Gatso types) make the road about 150 yards either side of them speed compliant, sometimes a lot less distance.
As far as being placed on accident blackspots, ideal world would be able to define precise locations. As it is, the submission and subsequent extrapolation of accident statistics mean that the length of the A123 or whatever is decreed a 'blackspot' between towns A and B. That distance could easily measure a few miles. The roads engineers and police authorities (not always the trafpol who deal with the accidents, mark you) then decide where the box is going to go.
Guess what? Its not always at the blackspot but somewhere on the length of A to B.......