The U.S. Congress passed the Standard Time Act of 1918 to establish standard time and preserve and set Daylight Saving Time across the continent. This act also devised five time zones throughout the United States: Eastern, Central, Mountain, Pacific, and Alaska. The first time zone was set on "the mean astronomical time of the seventy-fifth degree of longitude west from Greenwich" (England). In 1919, this act was repealed.

   President Roosevelt established year-round Daylight Saving Time (also called War Time) from 1942–1945. However, after this period, each state adopted its own DST, which proved to be disconcerting to television and radio broadcasting and transportation. In 1966, President Lyndon Johnson created the Department of Transportation and signed the Uniform Time Act. As a result, the Department of Transportation was given the responsibility for the time laws. During the oil embargo and energy crisis of the 1970s, President Richard Nixon extended DST through the Daylight Saving Time Energy Act of 1973 to conserve energy further. This law was modified in 1986, and Daylight Saving Time was reset to begin on the first Sunday in April (to spring ahead) and end on the last Sunday in October (to fall back).

The Daylight Saving Time Energy Act of 1973 was responsible for

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