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Daylight saving time in the United States is the practice of setting the clock forward by one hour during the warmer part of the year, so that evenings have more daylight and mornings have less. Most areas of the United States currently observe daylight saving time (DST), the exceptions being Arizona (except for the Navajo Nation, which does observe daylight saving time),〔("Most of Arizona Exempt from Daylight Saving Time" ), timeanddate.com. Retrieved February 14, 2013.〕 Hawaii,〔(【引用サイトリンク】title=Daylight Time )〕 and the overseas territories of American Samoa, Guam, the Northern Mariana Islands, Puerto Rico and the United States Virgin Islands. Currently, daylight saving time starts on the second Sunday in March and ends on the first Sunday in November, with the time changes taking place at 2:00 a.m. local time. With a mnemonic word play referring to seasons, clocks "spring forward and fall back"—that is, in springtime the clocks are moved forward from 2:00 a.m. to 3:00 a.m., and in fall they are moved back from 2:00 a.m. to 1:00 a.m. The following table lists recent past and near future starting and ending dates of daylight saving time in the United States: } | |md}} |- | | |md}} | |md}} |- | | |md}} | |md}} |- | | | |- | | |md}} | |md}} |- | | |md}} | |md}} |- | | |md}} | |md}} |} ==History of DST in the United States== 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 established standard time zones 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 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.〔(Source: CRS Report to Congress ) s:Congressional Research Service Report RS22284 Daylight Saving Time〕 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. In 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 states had no DST anywhere. 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.〔 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 winter 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).〔 The DOT, evaluating the plan of extending DST into March, reported in 1975 that "modest overall benefits might be realized by a shift from the historic six-month DST (May through October) in areas of energy conservation, overall traffic safety and reduced violent crime." However, DOT also reported that these benefits were minimal and difficult to distinguish from seasonal variations and fluctuations in energy prices.〔 Congress then asked the National Bureau of Standards (NBS) to evaluate the DOT report. Its report, "Review and Technical Evaluation of the DOT Daylight Saving Time Study" (April 1976), found no significant energy savings or differences in traffic fatalities. It did find statistically significant evidence of increased fatalities among school-age children in the mornings during the four-month period January–April 1974 as compared with the same period (non-DST) of 1973. NBS stated that it was impossible to determine, what, if any, of this increase was due to DST. When these data were compared between 1973 and 1974 for the months of March and April, no significant difference was found in fatalities among school-age children in the mornings.〔 In 1986 Congress enacted P.L. 99-359, amending the Uniform Time Act by changing the beginning of DST to the first Sunday in April and having the end remain the last Sunday in October.〔 These start and end dates were in effect from 1987 to 2006. The time was adjusted at 2:00 a.m. local time. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Daylight saving time in the United States」の詳細全文を読む スポンサード リンク
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