An ambiguous crime. The limits are clearly posted, but enforcement is highly inconsistent. Driving the speed limit has probably become indicative of old age or an attempt to avoid police interaction. Try strictly driving the posted limit for a while and you will find it socially unacceptable. While most traffic stops are rightly due to excessive violation, some are an excuse to investigate. A stop for speeding makes a great cover should the motorist complain. If they were driving slower than the social norm, or even the cars around them, there is no hard evidence to support their case.