I got curious about statistics on speeding and found this study on speeding.
http://www.ibiblio.org/rdu/sl-irre0.html I have no idea if this study is well sourced or not, but here are some claims I find interesting:
1. 70% of drivers exceed the speed limit.
"Driver compliance with speed limits is poor. On average, 7 out of 10 motorists exceeded the posted speed in urban areas. Compliance ranged from 3 to 99 percent. Compliance tended to be worse on low-speed roads, better on roads with prima facie limits, or where the speed limit was based on an engineering study. Better does not mean good compliance; less than 10 percent on [sic] the sites had more than 50-percent obedience with the posted speed."
2. Speed limits are supposed to be based on prevailing traffic patterns, but often are set much lower than the prevailing traffic patterns warrant. "
In a nationwide survey of current speed zoning practices, all states and most of the 44 localities reported using the 85th-percentile speed as the basic factor in setting speed limits. However, the posted speed is often set up to 10 mph lower than the prevailing speed based on a subjective consideration of other factors such as road-side development. The relative subjectivity of the speed zoning process points to the need to re-examine the criteria and procedures used in setting speed limits .... On many streets and highways the speed limit is set 8 to 12 mph below the prevailing 85th-percentile speed .... Many current speed limits coincide with 30-percentile speed, which is near the lower bound of safe travel speed. Speed limits should be set in the 70-to-90-percentile range or roughly 5 to 10 mph above the average speed to correctly reflect maximum safe speed." My best guess is that no city council member wants to be blamed as the one who approved a speed limit after someone gets hurt, so it's easiest to reduce the speed limit.
3. People who drive the very slowest are the most likely to get in accidents.
"The accident involvement rates on streets and highways in urban areas was highest for the slowest 5 percent of traffic, lowest for traffic in the 30-to-95-percentile range and increased for the fastest 5 percent of traffic. The relative involvement rate is a measure of the chance of being involved in an accident, and is a ratio of the percent of accidents in a given speed range to the percent of travel in the same speed range."
There are lots of other studies, but I have not read them yet.
http://www.nhtsa.gov/search?q=speeding&x=0&y=0
http://scholar.google.com/scholar?hl=en&q=speed+limit+driver&btnG=&as_sdt=1%2C33&as_sdtp=