In France drivers will flash their lights to warn you of police speed traps or other checks. (It's quite common for French police to stop and breathalyse all dr

In France drivers will flash their lights to warn you of police speed traps or other checks. (It's quite common for French police to stop and breathalyse all drivers on some rural road, especially on Sunday afternoons.) I have driven in France loads and have literally never reached a police roadblock or radar trap without being warned by a vehicle coming the other way.