I think that actually illustrates the above commenter's point about gray areas? the highway does not devolve into lethal chaos when people exceed the limit by 10 mph. even 20 mph over is not so bad when the relative speed among vehicles is low. or on the other hand, a few outliers are not a huge problem when proper lane discipline is maintained (ie, don't pass on the right, keep right except to pass). it's not a big deal if most people occasionally speed to get to an important appointment. it's also not catastrophic if a few people who can afford it take the hit and speed everywhere. mostly, it just offends our sense of fairness.
