Today, the Uniform Time Act of 1966 (15 U.S.C. This responsibility was transferred from the Interstate Commerce Commission to DOT when Congress created DOT in 1966. Local decisions on which time zone to adopt were usually influenced by the time used by the railroads.įederal 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. States and municipalities then adopted one of the four zones, which were the eastern, central, mountain, and Pacific Time zones. 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 do not have the authority to choose to be on permanent Daylight Saving Time. Under the Uniform Time Act, States may choose to exempt themselves from observing Daylight Saving Time by State law. If a State chooses to observe Daylight Saving Time, it must begin and end on federally mandated dates. Nor does DOT have any role to play in a State's determination whether to observe Daylight Saving Time. DOT regulations at 49 CFR part 71 contain the official listing of the Nation's time zones.ĭOT 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. The oversight of time zones was assigned to DOT because time standards are important for many modes of transportation. Department of Transportation (DOT) oversees the Nation's time zones. Five states, namely Colorado, New Mexico, Wyoming, Utah, and Montana, are included within the Mountain Time Zone.The U.S. In the US, this time zone is generally known as Mountain Time (MT). The Mountain Time Zone (MT) observes standard time by subtracting 7 hours from UTC (UTC-07:00) and 6 hours during DST (UTC-06:00). PST is one hour ahead of Hawaii and Alaska Time Zones, and at least one hour behind the other time zones. During DST, an offsite time of UTC-7 is used. The standard time within this zone is observed by subtracting 8 hours from UTC (UTC-8). The Pacific Time Zone (PT) encompasses the western states of the US, western Mexico, and western Canada. The clock time in the Alaska Time Zone is based on the mean solar time at 135 degrees west of Greenwich Observatory. Standard time is observed in this time zone by subtracting 9 hours from UTC (UTC-09:00) and 8 hours during DST (UTC-08:00). The Alaska Time Zone encompasses almost the entire state of Alaska. Some of the major metropolitan areas under this time zone include Honolulu, Hilo, and Kapaa. The time zone observes Hawaii-Aleutian Standard Time (HAST), which is obtained by subtracting 10 hours from UTC (UTC-10:00). These two areas do not use daylight saving time. The Hawaii-Aleutian Time Zone derives its name from two areas: Hawaii and the Aleutian Islands in Alaska. Time Zones Within the 50 US States Hawaii-Aleutian Time Zone The time zones are defined by their hourly offset from UTC. DST is not observed in the states of Hawaii and Arizona, and some US territories including Puerto Rico, Guam, American Samoa, and the Virgin Islands. Most states observe Daylight Saving Time (DST), which begins at 0200 hours on the second Sunday of March and runs until 0159 hours on the first Sunday of November. The other three time zones are used in US territories: the Atlantic Time Zone is followed in Puerto Rico and the US Virgin Islands the Chamorro Time Zone is followed in Guam and the Samoa Time Zone is followed in American Samoa. However, the 50 states are spread across six standard time zones: Pacific, Central, Mountain, Eastern, Alaska, and Hawaii. United States Time Zonesīy law, time in the United States (US) and its possessions is divided into nine standard time zones. UTC time either changes backward or forward by one hour for every 15 degrees west or east of the prime meridian. The local time in a given time zone is defined by its offset from Coordinated Universal Time (UTC), which is the primary time standard used throughout the world. Time zones are regions on the globe that observe the same standard time. Further advances led to the concept of standard time zones. Apparent and mean solar time may differ by up to 15 minutes. When mechanical clocks became common in the 19th century, mean solar time was used. For example, a sundial was used to estimate the time based on the Sun's apparent position in the sky. Before the invention of clocks, the time of day was determined by apparent solar time.
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