Speeding is commonly defined as exceeding the posted speed limit or driving too fast for conditions. All United States roads have a speed limit. General State and municipal speed limits apply to all roads in a class, such as rural interstates or local streets. States and municipalities may establish speed zones with their own speed limits on road segments where the general speed limit is thought to be inappropriate. Drivers generally believe they will not be ticketed for speeds less than 5 or sometimes 10 mph over the posted limit3.

Speeding is common, and on some roads almost universal. About 80 percent of all drivers in NHTSA’s 2002 national survey reported they exceeded the posted speed limit on each type of road - interstate, non-interstate multi-lane, two-lane, and city streets - within the past month, and about one-third reported this behavior on the day of the interview. One-third of all drivers reported that they often or sometimes drive at least 10 mph faster than most other vehicles. Yet two-thirds of drivers felt that other speeding drivers pose a major threat to their personal safety4.

NHTSA considers a crash to be speeding-related if a driver was charged with a speeding-related offense or if the investigating officer indicated that racing, driving too fast for conditions, or exceeding the posted speed was a contributing factor in the crash. Using this definition, NHTSA estimated that speeding was a contributing factor in 31 percent of fatal crashes in 2003 and speeding-related crashes claimed 13,380 lives5. NHTSA’s early traffic fatality estimates project about the same levels in 2004: 13,087 fatalities, or 31 percent of all traffic fatalities, involved speeding6.

Speeding-related Traffic Fatalities, 1983-20037

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Speeding can be dangerous on all roads. In 2003, half of the speed-related traffic fatalities occurred on roads posted at 50 mph or less and one-quarter occurred on roads posted at 35 mph or less8.

Speeding affects both the probability of a crash and the severity of injuries produced by a crash. Some research documents indicate three effects of speed on crashes and injuries. First, the probability of a crash increases substantially as a vehicle’s travel speed increases9. Other research indicates, the probability of a crash increases as a vehicle’s travel speed rises above or falls below the average travel10. Third, in a crash, injury severity is proportional to the impact forces on a person, which in turn are related to the square of the change in speed.

3 Governors Highway Safety Association (2005). Survey of the States: Speeding.

4 R Compton (2005). Speeding: Who, When, Where. Presentation to the National Forum on Speeding, slides 27, 29, and 35.

5 Compton, slides 3 and 4.

6 NHTSA (2005). Motor Vehicle Traffic Crash Fatalities and Injuries: 2004 Projections. DOT HS 809 862.

7 Compton, slide 5.

8 Compton, slide 22; NHTSA (2005), Traffic Safety Facts 2003. DOT HS 809 775.

9 S Ferguson (2005). Relation of Speed and Speed Limits to Crashes. Presentation to the National Forum on Speeding, slides 10-11.

10 Ferguson, slides 3-11.