Also, I once asked a rav a sheila about whether breaking the speed limit is a violation of dina d’malchusa. The answer I received was that violating traffic laws that are commonly enforced is a violation of dina d’malchusa. So driving 2 mph over the speed limit would not be a dina d’malchusa problem, but driving 12 mph over the speed limit probably would be.
So those of you who care about following halacha but like to drive over the speed limit would be advised to consult your Rav before doing so.