[agumonkey]

often I wish that roads had "wiper" cars that would fill the whole width and drive at the maximum limit and not more. :)

[PappaPatat]

Much better solution: https://en.wikipedia.org/wiki/SPECS_(speed_camera)

Basically two cameras at a set distance that measure the time it took from location A to B and calculates the average speed. Works like a charm: no more speed differences.