The report examines the results of a survey of US States following the raising of the speed limit to 65 mph on Interstate highways. Evaluating the effects of the 65 mph speed limit on rural Interstate roads is complicated by the relative safety of these roads. First, rural Interstate roads have fewer fatalities per hundred million vehicle miles travelled than do other roads. In 1988 (when forty states had raised the speed limit on most of the rural Interstate system), the fatality rate was 1.6 on rural Interstate roads and 0.9 on urban Interstate roads, but was 2.7 on non-Interstate roads. Second, rural Interstate fatalities account for only five percent of total traffic fatalities each year. Any rural Interstate fatality change has a relatively small effect on total highway fatalities. Third, many individual states have very few rural Interstate fatalities. Annual fatality changes in these states may be the result of chance. These three factors must be recognised in evaluating the effects of the 65 mph speed limit. The available data show that the number of rural Interstate fatalities and the rural Interstate fatality rate increased after the speed limit was raised to 65 mph. Statistical models were used to refine the estimates of these changes by including additional historical information about the relationships between fatalities and travel. It is estimated that rural Interstate fatalities increased 16 percent in 1987 (the first year of the higher speed limit) compared to 1986 (for the full year, in states that raised the speed limit at some time in 1987); the increase was 10 percent after accounting for travel increases on these roads.
Samenvatting