Just to add to the selective legislation factor.

There are roads in the US where the speed limit is 55mph. Given no selective legislation then I should be able to travel on any road at that speed. Now if that were the case I might have to be educated on the possible impact of driving 55mph in a 10mph zone but without any legislated consquence I wouldn't have to abide by those limits if I didn't feel like it as there is no disincentive.