As I said, I've heard of this but have never seen it and to date it is only possible that it exists in the USA. Today, however, I did read this about the police in France.
|In some cases, the gendarmes locate themselves at toll booths on motorways, and fine drivers who have arrived at the exit toll booth too soon since taking a ticket at the entry toll booth. A common tactic by long-distance drivers is therefore to take any breaks (for meals etc) on tolled sections of road rather than untolled sections, thereby reducing their average speed between the toll booths.|
The French are usually fairly quick to pick-up on technology so it surprised me to read that they were using their police force to issue the fines and not automating it.