Originally Posted by
PeteHski
Well that’s the thing. If the speed limit was enforced to say 1 mph then driving at an indicated speed limit might get you a ticket due to the slightest of measurement error. As I said, we can argue about tolerances and I just stated what our police forces use. It is not a social convention, it is what guarantees them a conviction without having to argue about instrument calibrations etc in court.
I agree 10 mph over a low speed limit of say 30 would be nonsense, which is why percentage tolerances generally work better.
When I was visiting my in-laws years ago, they specifically warned me about a small town in a valley about their speed limit policies. They actually gave out tickets for going 1 mile over the speed limit. To challenge that citation, one has to go back to their court and no one wants to travel back to that town to deal with it and people simply paid the fine. A news reporter from a large city met the same fate while driving through this town. He wrote a small article in his paper, calling their police and traffic court Gestapo.
Apparently, their rules were strictly enforced only on the out of state cars.
Difference of approximately 5MPH at highway speeds tends to be difficult to conclusively prove as intentional because of some errors in speedometers (tire pressure, wear etc), it makes sense to have some latitude.