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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), Hawaii, and the overseas territories of Puerto Rico, American Samoa, Guam, the Northern Mariana Islands, and the United States Virgin Islands.
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 spring (technically late winter) 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 am to 1:00 am.
The following table lists recent past and near future starting and ending dates of daylight saving time in the United States:
|2010||March 14||November 7|
|2011||March 13||November 6|
|2012||March 11||November 4|
|2013||March 10||November 3|
|2014||March 9||November 2|
|2015||March 8||November 1|
|2016||March 13||November 6|
|2017||March 12||November 5|
|2018||March 11||November 4|
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. 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.
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.
By the Energy Policy Act of 2005, daylight saving time (DST) was extended in the United States beginning in 2007. As of that year, DST begins on the second Sunday of March and ends on the first Sunday of November. These changes result in a DST period that is five or four weeks longer than previously (for April 1 falling on Monday to Thursday resp. Friday to Sunday). In 2008 daylight saving time ended at 2:00 a.m. DST (0200) (1:00 a.m. ST) on Sunday, November 2, and in 2009 it began at 2:00 a.m. (3:00 a.m. DST) on Sunday, March 8. Wyoming Senator Michael Enzi and Michigan Representative Fred Upton advocated the extension from October into November especially to allow children to go trick-or-treating in more daylight.
Under Section 110 of the Act, the U.S. Department of Energy was required to study the impact of the 2007 DST extension no later than nine months after the change took effect. The report, released in October 2008, reported a nationwide electricity savings of 0.03% for the year of 2007.
An October 2008 study conducted by the University of California at Santa Barbara for the National Bureau of Economic Research found that the 2006 DST adoption in Indiana increased energy consumption in Indiana by an average of 1%. Although energy consumption for lighting dropped as a result of the DST adoption, consumption for heating and cooling increased by 2 to 4%. The cost to the average Indiana household of the DST adoption was determined to be $3.29 per year, for an aggregate cost of $1.7 million to $5.5 million per year.
Under the Standard Time Act of 1918, as amended by the Uniform Time Act of 1966, moving a state or an area within a state from one time zone to another requires a regulation issued by DOT. The governor or state legislature may initiate a request for the state or any part of the state; the highest elected officials in the county may make a request for that county. The standard in the statute for such decisions is the convenience of commerce in that area. The convenience of commerce is defined broadly to consider such circumstances as the shipment of goods within the community; the origin of television and radio broadcasts; the areas where most residents work, attend school, worship, or receive health care; the location of airports, railway, and bus stations; and the major elements of the community's economy.
After receiving a request for altering a time zone, DOT determines whether it meets the requirement of minimum statutory criteria before issuing a notice of proposed rulemaking, soliciting public comment and scheduling a public hearing. Usually the hearing is held in the area requesting the change so that all affected parties can be represented. After the close of the comment period, the comments are reviewed and appropriate final action taken. If the Secretary agrees that the statutory requirement has been met, the change is instituted, usually at the next changeover to or from DST.
Under the Uniform Time Act, moving an area on or off DST is accomplished through legal action at the state level. Some states require legislation while others require executive action such as a governor's executive order. Information on procedures required in a specific state may be obtained from that state's legislature or governor's office. Although it may exempt itself, if a state decides to observe DST, the dates of observance must comply with federal legislation.
Alaska observes DST although there had been a recent[vague] statewide move to abolish it. As of July 24, 2006[update], Alaska's lieutenant governor Loren Leman approved a petition to collect signatures to put the initiative measure on the ballot by 2008. Due to its high latitude, Alaska has nearly round-the-clock daylight during summer and DST is seen by some Alaskans as unnecessary and a nuisance.
Another issue is that the Alaskan mainland's single time zone, which approximates solar time in the capital, Juneau, leads to a large disparity between civil time and solar time for much of the state, with solar noon occurring as late as 2:00 p.m. in the population centers of Anchorage and Fairbanks, and as late as 3:00 p.m. by the clock in places like Nome. In Fairbanks, for example, sunset occurs well after civil midnight in the summer. Others argue that ending daylight saving time will place Alaska as much as five hours from Eastern Daylight Time, making coordination of travel and phone conversations more difficult.
Arizona observed DST in 1967 under the Uniform Time Act because the state legislature did not enact an exemption statute that year. In March 1968 the DST exemption statute was enacted and the state of Arizona has not observed DST since 1967. This is in large part due to energy conservation: Phoenix and Tucson are among the hottest US metropolitan areas during the summer, resulting in more power usage from air conditioning units and evaporative coolers in homes and businesses. An extra hour of sunlight while people are active would cause people to run their cooling systems longer, thereby using more energy. The summer of 1967 was the one year that DST was observed. The State Senate Majority leader at the time owned drive-in theaters and was nearly bankrupted due to DST, as movies could not start until 10:00 p.m. at the height of summer, well past normal hours for most Arizona residents. There has never been any serious consideration of reversing the exemption.
The Navajo Indian Reservation, which extends into two adjacent states, Utah and New Mexico, does observe daylight saving time. The Hopi Reservation, which is entirely within the state of Arizona and is an enclave of the Navajo Indian Reservation, does not observe DST.
Colorado Springs Gazette columnist Ralph Routon wrote a series of columns in 1999 promoting placing all of Colorado on year-round DST in order to save state residents the "aggravation of resetting their clocks every six months." The idea gathered popular support in Colorado Springs and the attention of the state's larger newspapers, but when state Senator MaryAnne Tebedo attempted to present the idea to the state legislature, her research uncovered federal laws forbidding the state-initiated extension of daylight saving time. Still determined to relieve Coloradans of the need to change their clocks, Tebedo introduced the only bill legally permitted to her: a proposal to exempt the state of Colorado from DST. The bill did not advance from committee during the 2000 legislative session.
Daylight time is less useful in Florida than in many other states because of its southern location[vague] near the western boundary of its timezone. Without DST, Miami, for instance, would experience similar sunrise and sunset times throughout the year to cities such as Honolulu or Hong Kong, both of which have abandoned DST for decades. There is opposition to DST in Florida. State senator Bill Posey introduced a bill in March 2008 to abolish daylight time in the state and keep Florida on year-round standard time. Because Florida straddles two time zones, the Florida legislature has the option of returning all or part of the state to standard time along time zone boundaries. [dated info]
Because of Hawaii's tropical latitude, there is not a large variation in daylight length between winter and summer. Advancing the clock in Hawaii would make sunrise times close to 7:00 a.m. even in June. Most of the inhabited islands are located close to the west end of the Hawaii-Aleutian time zone, but Oahu, Kauai, and Niihau are located more than 7 degrees west of the Hawaii-Aleutian time zone's meridian and should, theoretically, be located in the next time zone to the west. (Until about 1946 Hawaiian standard time was based on longitude 157.5 deg west rather than 150 deg.)
On April 26, 1933, the Territorial Legislature enacted a bill placing Hawaii on daylight saving time from the last Sunday in April (April 30 in that year) to the last Sunday in September, but the law was repealed three weeks later on May 21, 1933. During World War II between February 9, 1942 and September 30, 1945, Hawaiian Standard Time was advanced one hour to so-called "Hawaiian War Time," effectively placing the territory on year-round daylight saving time.
From 1970 until 2006, most of Indiana in the Eastern Time Zone did not observe daylight saving time, but the entire state started to do so in April 2006 after eight counties in western Indiana were shifted from the Eastern Time Zone to the Central Time Zone. One goal for observing DST was to get more Indiana counties observing the same timezone; formerly, 77 counties observed EST, 5 observed EST/EDT (the EDT usage being unofficial only), and 10 observed CST/CDT. At present, Indiana has 12 counties observing Central Daylight Time while the remaining 80 counties observe Eastern Daylight Time. Those counties observing CST are near or in the Chicago metropolitan area.
In 1967 the Michigan Legislature adopted a statute, Act 6 of the Public Acts of 1967, exempting the state from the observance of DST. The exemption statute was suspended on June 14, 1967, however, when the referendum was invoked. From June 14, 1967 until the last Sunday in October, 1967, Michigan observed DST, and did so in 1968 as well. The exemption statute was submitted to the voters at the General Election held in November 1968, and, in a close vote, the exemption statute was sustained. As a result, Michigan did not observe DST in 1969, 1970, 1971, or 1972. In November 1972, an initiative measure, repealing the exemption statute, was approved by the voters. Michigan again observed DST in 1973, and has continued to do so since then.
(Notice that Michigan straddles two time zones. The Upper Peninsula counties which border Wisconsin (namely Gogebic, Iron, Dickinson, and Menominee counties) are in Central Time, and the rest of the state, including the entire Lower Peninsula, is in Eastern Time.)
In 2005, Nevada Assembly Bill 18 would have exempted Nevada from daylight saving time. The bill's author, Assemblyman Bob McCleary, D-North Las Vegas, argued that because of southern Nevada's desert climate, it would reduce power usage during the peak summer months by reducing the time that people would operate their home air conditioners. The result of not observing DST, however, would place the state in an odd time configuration relative to neighboring states. Because it is on the eastern edge of the Pacific Time Zone, Nevada (PST) would be two hours behind Utah (MDT), its eastern neighbor, and one hour behind California (PDT), its western neighbor. In the summer, it would therefore be the same time in Nevada (PST) as it would be in the majority of Alaska (AKDT). The bill died without a vote.
Republican Rep. Curry Todd of Collierville has sponsored a bill to establish permanent Daylight Saving Time in Tennessee, to become effective July 2014. The bill passed out of subcommittee in mid February 2014, despite some concerns from other lawmakers. The bill was expected to go to vote by the House State Government Committee in late February, but no decision has been announced as of early March 2014.
While neighboring Samoa began observing DST in September 2010, the smaller American Samoa cannot legally follow because of the DST observation period mandated by the Uniform Time Act. This period is actually wintertime in this Southern Hemisphere territory.
Many computer operating systems (such as Microsoft Windows, Linux, UNIX, and OS X) and programming languages (such as Java, perl, and most shell languages) allow a local time zone setting in the format of (Standard Time Zone abbreviation)(UTC hour difference)(Daylight Saving Time Zone abbreviation). This allows programs and programming languages that must do calculations based on local time to more easily calculate differences between local time and UTC, as well as knowing whether calculations should be changed during Daylight Saving Time. For example, a time zone setting of EST5EDT indicates that local time on the computer is 5 hours behind UTC and should be adjusted for Daylight Saving Time.
|Time Zone||Standard Time||Daylight Saving Time||TZ|
|Eastern Time Zone||EST (UTC-5)||EDT (UTC-4)||EST5EDT|
|Central Time Zone||CST (UTC-6)||CDT (UTC-5)||CST6CDT|
|Mountain Time Zone||MST (UTC-7)||MDT (UTC-6)||MST7MDT|
|Pacific Time Zone||PST (UTC-8)||PDT (UTC-7)||PST8PDT|
|Alaska Time Zone||AKST (UTC-9)||AKDT (UTC-8)||AKST9AKDT|
|Hawaii-Aleutian Time Zone||HAST (UTC-10)||HADT (UTC-9)|
Aleutian Islands only
Official Civil Time Distribution
Quasi-governmental time distribution systems