The GPS units (e.g. Garmin) which are fitted in private light aircraft are required to record their journey details so that, like the Black Box in commercial aircraft, they can be interrogated after an accident as part of the Air Accident Investigation. Are there GPS units for automobiles that have the same facility, so that a driver who is followed by a police car or flashed by an inaccurate radar trap can download the exact details and argue that his speed was not as they measured?