Does Speed Cause Accidents?

What about all those "speed-related" Accidents?

Quoted from the Proceedings of National Highway Safety Bureau Priorities Seminar "Speed-Related Accident Countermeasures and Their Priorities," Vol. 5, Fredericksburg, Virignia, July 18-30, 1969. Cited in Volume 2 of the 1970 study on Maximum Speed Limits:


In discussing speed in relation to accidents it is well to delineate the several senses in which the term might be used. It is useful to think of speed in the following contexts [my bolding added]:
  1. Very high speed - speed approaching and exceeding 100 mph. Under these conditions, the speed factor dominates as a causative agent, since few if any of the elements of the overall vehicle-driver- highway system have been designed to accommodate travel at this speed.
  2. Excessive speed for conditions - speeds ranging from zero to design speeds. This category of speeding encompasses many of the speeding citations issued in connection with accidents.
    [Note how the National Highway Traffic Safety Administration (NHTSA) focuses your attention on "exceeding the posted speed limit" and hammers on speeding, but presents facts primarily on "driving too fast for conditions"! See for example their "Fact Sheet" {link to NHTSA site}.]
  3. Differential speed or speed gradients [speed "variance"] in the traffic stream - in part, an overlapping set with excessive speed but also includes inadequate speed. Differential speed and the related variable 'acceleration noise' figure prominently in the safe and efficient flow of traffic. Large speed differentials are seldom if ever cited as a contributing cause, the factor being implicit in other improper driving categories such as following to close[ly] and reckless driving.
With these connotations of speed in mind it can be appreciated that speed is very often not a singular or an explicit variable in the accident equation. Thus, efforts to treat speed as an accident cause are often reduced to treating symptoms arising from the synergy of speed and many other system factors.

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Updated June 06, 1997