I expect that applies equally well to the UK with gantries of ANPR cameras over major motorways as well as portable ones in laybys, like the one I saw this morning on the A1 leaving Edinburgh. It wasn't a police car, though, but a dedicated "road tax enforcement" vehicle running it.

I was reminded by a colleague today of a quote attributed to Roger Needham, something along the lines of "privacy is a transient condition in between people realising there isn't an omniscient god, and government realising there was a vacancy" (quoting second hand from memory)