<P> During World War I, in an effort to conserve fuel, Germany began observing DST on May 1, 1916 . The rest of Europe soon followed . The plan was not adopted in the United States until the Standard Time Act of March 19, 1918, which confirmed the existing standard time zone system and set summer DST to begin on March 31, 1918 (reverting October 27). The idea was unpopular and Congress abolished DST after the war, overriding President Woodrow Wilson's veto . DST became a local option and was observed in some states until World War II, when President Franklin Roosevelt instituted year - round DST, called "War Time", on February 9, 1942 . It lasted until the last Sunday (the 30th) in September 1945 . After 1945 many states and cities east of the Mississippi River (and mostly north of the Ohio and Potomac rivers) adopted summer DST . </P> <P> From 1945 to 1966 there was no federal law on daylight saving time, so localities could choose when it began and ended or drop it entirely . As of 1954, only California and Nevada had statewide DST west of the Mississippi, and only a few cities between Nevada and St. Louis . In the 1964 Official Railway Guide, 21 of the 48 contiguous states had no DST anywhere . </P> <P> By 1962, the transportation industry found the lack of consistency confusing enough to push for federal regulation . The result was the Uniform Time Act of 1966 (P.L. 89 - 387). Beginning in 1967, the act mandated standard time within the established time zones and provided for advanced time: clocks would be advanced one hour beginning at 2: 00 a.m. on the last Sunday in April and turned back one hour at 2: 00 a.m. on the last Sunday in October . States were allowed to exempt themselves from DST as long as the entire state did so . If a state chose to observe DST, the time changes were required to begin and end on the established dates . In 1967, Arizona and Michigan became the first states to exempt themselves from DST (Michigan would begin observing DST in 1972). In 1972, the act was amended (P.L. 92 - 267), allowing those states split between time zones to exempt either the entire state or that part of the state lying within a different time zone . The newly created Department of Transportation (DOT) was given power to enforce the law . As of 2014, the following states and territories are not observing DST: Arizona, Hawaii, American Samoa, Puerto Rico, and the Virgin Islands . </P> <P> During the 1973 oil embargo by the Organization of Arab Petroleum Exporting Countries (OAPEC), in an effort to conserve fuel, Congress enacted a trial period of year - round DST (P.L. 93 - 182), beginning January 6, 1974, and ending April 27, 1975 . The trial was hotly debated . Those in favor pointed to increased daylight hours in the summer evening: more time for recreation, reduced lighting and heating demands, reduced crime, and reduced automobile accidents . The opposition was concerned about children leaving for school in the dark . The act was amended in October 1974 (P.L. 93 - 434) to return to standard time for the period beginning October 27, 1974, and ending February 23, 1975, when DST resumed . When the trial ended in 1975, the country returned to observing summer DST (with the aforementioned exceptions). </P>

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