<P> According to the National Research Council, there was a decrease in fatalities of about 3,000 to 5,000 lives in 1974, and about 2,000 to 4,000 lives saved annually thereafter through 1983, due to slower and more uniform traffic speeds since the law took effect . Later, the National Academies wrote that there is "a strong link between vehicle speed and crash severity (which) supports the need for setting maximum limits on high - speed roads," but that "the available data do not provide an adequate basis for precisely quantifying the effects that changes in speed limits have on driving speeds, safety, and travel time on different kinds of roads ." The Academies report also noted that on rural interstates, the free - flowing traffic speed should be the major determinant of the speed limit, because "Drivers typically can anticipate appropriate driving speeds ." This is due, in part, to the strong access control in these areas but also is an acknowledgement of the difficulty of enforcing the 55 mph (90 km / h) speed limit in these areas . </P> <P> A Cato Institute report showed that the safety record worsened in the first few months of the new speed limits, suggesting that the fatality drop found by the NRC was a statistical anomaly that regressed to the mean by 1978 . After the oil crisis abated, the NMSL was retained mainly due to the possible safety aspect . </P> <P> Insurance Institute for Highway Safety analysts wrote three papers that argue that increase from 55 to 65 mph (90 to 105 km / h) on rural roads led to a 25% to 30% increase in deaths (1 / 3 from increased travel, 2 / 3 from increased speed) while the full repeal in 1995 led to a further 15% increase in fatalities . In contrasting work, researchers at University of California Transportation Science Center argue that the interstates in question are only part of the equation, one also must account for traffic moving off the relatively more dangerous country roads and onto the relatively safer interstates . Accounting for this they find that raising rural speed limits to 65 mph (105 km / h) caused a 3.4% to 5.1% decrease in fatalities . </P> <P> In 1998, the U.S. Transportation Research Board footnoted an estimate that the 1974 National Maximum Speed Limit (NMSL) reduced fuel consumption by 0.2 to 1.0 percent . Rural interstates, the roads most visibly affected by the NMSL, accounted for 9.5% of the U.S.'s vehicle - miles - traveled in 1973, but such free - flowing roads typically provide more fuel - efficient travel than conventional roads . </P>

When did the speed limit change from 55 to 65