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Uniform Time


The U.S. Department of Transportation (DOT) oversees the Nation's time zones.  The oversight of time zones was assigned to DOT because time standards are important for many modes of transportation.  DOT regulations at 49 CFR part 71 contain the official listing of the Nation's time zones.

DOT also oversees the Nation's uniform observance of Daylight Saving Time; however, DOT does not have the power to repeal or change Daylight Saving Time.  Nor does DOT have any role to play in a State's determination whether to observe Daylight Saving Time.  If a State chooses to observe Daylight Saving Time, it must begin and end on federally mandated dates.  Under the Uniform Time Act, States may choose to exempt themselves from observing Daylight Saving Time by State law.  States do not have the authority to choose to be on permanent Daylight Saving Time.


In 1883, U.S. and Canadian railroads adopted a four-zone system to govern their operations and reduce the confusion resulting from some 100 conflicting locally established “sun times” observed in terminals across the country.  States and municipalities then adopted one of the four zones, which were the eastern, central, mountain, and Pacific Time zones.  Local decisions on which time zone to adopt were usually influenced by the time used by the railroads. 

Federal oversight of time zones began in 1918 with the enactment of the Standard Time Act, which vested the Interstate Commerce Commission with the responsibility for establishing boundaries between the standard time zones in the continental United States.  This responsibility was transferred from the Interstate Commerce Commission to DOT when Congress created DOT in 1966. 

Today, the Uniform Time Act of 1966 (15 U.S.C. §§ 260-64) establishes a system of uniform Daylight Saving Time throughout the Nation and its possessions, and provides that either Congress or the Secretary of Transportation can change a time-zone boundary.

Time Zones

The time zones established by the Standard Time Act, as amended by the Uniform Time Act, are Atlantic, eastern, central, mountain, Pacific, Alaska, Hawaii–Aleutian, Samoa, and Chamorro. 


DOT is responsible for fostering and promoting uniform time observance.  If your locality is not observing the proper time, please email  

Further Reading