Self-monitoring of driving speed.

•In vehicle data recorders (IVDR) increase traffic safety, but create a “big brother” problem.•The big brother concern can be addressed by allowing an easy turn-off option, but this option might increase speed variability.•A simulator study shows that the negative effects of the turn-off option are minimized by using gentle fines.•Gentle IVDR based small fines with turn-off option can be highly effective.