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Effects of Raising and Lowering Speed Limits

October 1992

U.S. Department of Transportation, Federal Highway Administration


This experiment evaluates the outcomes of raising and lowering speed limits on driving behavior and accident prevalence. Overall, results show that lowering speed limits by 20 mph and raising speed limits by 15 mph had very small effects on actual driving speeds. Further, they find that lowering speed limits did not reduce the occurrence of accidents, nor did raising speed limits increase the occurrence of accidents.

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Policy Implications

These findings suggest that drivers do not tend to adhere to posted speed limits, rather they drive at the speeds they feel are appropriate. Therefore, policy looking to decrease accidents should focus elsewhere, as decreases in speed limits are unlikely to produce satisfactory results.

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