Someone else mentioned speed limit enforcement (or really a lot of traffic laws generally). There's essentially a contract between people and the state whereby most people accept that there are traffic laws that they'll loosely follow and the state can enforce the laws but will almost universally ignore or miss minor infractions.

The situation would be quite a bit different in the US if automated tickets were sent out (or money were just deducted from a bank account) every time someone went 5 miles per hour over the speed limit.