<P> The limit's effect on highway safety is unclear . During the time the law was enacted and after it was repealed automobile fatalities decreased, and this was widely attributed mainly to automobile safety improvements, owing to an increase in the safety of cars themselves . This decrease in fatalities from automobile accidents makes figuring out the actual impact of the law difficult . Although the vast majority of states reported fewer traffic deaths in 1974 compared with 1973, there were in fact three states where traffic deaths actually increased in 1974, 1975 and 1976, compared to 1973, notwithstanding the 55 mph (90 km / h) speed limit: Alaska, New Hampshire and Wyoming . </P> <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>

When was the 55 mph speed limit repealed