Toll to toll - were you speeding?

I have driven on toll roads where you get a ticket at the beginning of the toll section and when you exit the toll road through a slip road or at the end of the toll section then you punch your ticket and pay for the section of highway that you used. I have also heard of this type of toll road giving you a fine at the same time as the charge for the section of road you were using when you exit. When you put your ticket in the machine at the exit toll, it reads the time you entered the toll road and if your average speed from start to exit is higher than the speed limit then you've obviously been speeding so it fines you for that as well.

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.