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In November 1995, Congress enacted the National Highway System Designation Act, which among other provisions, repealed the national maximum speed limit law. This allowed each state to establish maximum speed limits on all roads for the first time since 1974, when a national maximum speed limit of 55 mph was established in response to a severe fuel shortage. Federal laws were revised in 1987 to permit states to raise speed limits on qualified sections of rural interstate highways to 65 mph; all other roads, including urban interstates and freeways, remained subject to the 55 mph speed limit. Thirty-eight states raised speed limits on rural interstates in 1987, and two additional states followed suit in 1988. While the basis for enactment of the original national maximum speed limit was fuel conservation, the policy also produced substantial safety benefits.1,2 These safety benefits prompted Congress to retain the national maximum speed limit even after concerns about vehicle fuel supplies had subsided.
Following implementation of increased speed limits in 1987 on rural interstates, researchers found that the higher limits were associated with higher traffic speeds and that raising speed limits increased the proportion of vehicles traveling at very high speeds. Freedman and Williams monitored car and truck speeds at 20 sites in five states that raised speed limits to 65 mph and at 34 locations in six states that retained the 55 mph limit, and found that the proportions of vehicles traveling at high speeds were substantially greater in the 65 mph states.3 Freedman and Esterlitz analyzed traffic speeds on rural interstates in Virginia before and after the speed limit was increased from 55 to 65 mph and reported an immediate jump in traffic speeds as well as significant increases in the proportion of vehicles exceeding 70 mph, and a continuous increase in speeds over time.4 In neighboring Maryland, which retained a 55 mph speed limit, increases in travel speed were not observed. The National Highway Traffic Safety Administration (NHTSA) analyzed speed data from 18 states and estimated that three times as many vehicles were traveling faster than 70 mph in the fall of 1988, compared with the fall of 1986, and that 11 times as many vehicles were traveling faster than 80 mph.5 Increases in rural interstate traffic...