A friend of mine was traveling across france on a motorcycle (this was decades ago) and one day had to get home to england quite quickly. So he got on the tollway and went quickly. But apparently they checked entrance and exit times on the tickets and would calculate your speed, so he "lost" his ticket and paid the max cost to be safe. I guess it worked.
There are a lot of automatic speed radars (at a single point), and a bit fewer average speed radars but they work over a few km at most (and don't interact with the toll).
He told me they check the entrance time on the ticket and when you get off at the exit they know approximately how long it should take you. And they would wave you off to the side if you made it say 120 miles in an hour instead of two. This was a long time ago.
