enacted and President Gerald Ford signed into law the Federal-Aid Highway Amendments of 1974 on January 4, 1975. Safety impact The limit's effect on highway safety is unclear. Both during the time the law was enacted and after it was repealed, automobile fatalities decreased, which was widely attributed mainly to automobile safety improvements, owing to an increase in the safety of cars themselves, and the passage of mandatory seat belt legislation by all states except New Hampshire from the mid-1980s to the early 1990s. 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. 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 because of 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 observed that on rural interstates, the free-flowing traffic speed should be the major determinant of the speed limit: "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. 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. Insurance Institute for Highway Safety analysts wrote three papers that argue that increase from on rural roads led to a 25% to 30% increase in deaths (1/3 from