Most U.S. residents set their clocks one hour forward in spring and one hour back in fall. However, residents of Arizona and Hawaii—along with the U.S. territories of Puerto Rico and the Virgin Islands, among others—will do nothing. Those locales never deviated from standard time within their particular time zones.
Contrary to popular belief, no federal rule mandates that states or territories observe daylight saving time.
Federal law simply stipulates that areas that do switch back to standard time at 2 a.m. on the last Sunday in October.
Likewise, the rule requires that regions that observe daylight saving time, or DST, begin the period at the same time on the first Sunday in April.
This is the last year, however, in which daylight saving time will fall within those days.
In 2005, the U.S. Congress passed a law extending DST by one month as of 2007. Next year, daylight saving time will begin three weeks earlier, on March 11, and end a week later, on November 4.
While the U.S. Naval Observatory in Washington, D.C., sets what is known as standard time in the country through its maintenance of atomic clocks, the observatory has nothing to do with daylight saving time.
Oversight of DST first resided with the Interstate Commerce Commission. In 1966, the U.S. Congress transferred that responsibility to the newly created Department of Transportation. Congress ordered the agency to "foster and promote widespread and uniform adoption and observance of the same standard of time within and throughout each such standard time zone."
So why is a transportation authority in charge of time laws? Bill Mosley, a public affairs officer at the U.S. Department of Transportation, explains that it all dates back to the heyday of railroads.
"In the early 19th century … localities set their own time," Mosley said. "It was kind of a crazy quilt of time, time zones, and time usage. When the railroads came in, that necessitated more standardization of time so that railroad schedules could be published."
In 1883 the U.S. railroad industry established official time zones with a set standard time within each zone. Congress eventually came on board, signing the railroad time zone system into law in 1918.
The only federal regulatory agency in existence at that time happened to be the Interstate Commerce Commission, so Congress granted the agency authority over time zones and any future modifications that might be necessary.
Part of the Act of 1918 also legislated for the observance of daylight saving time nationwide. That section of the act was repealed the following year, and DST thereafter became a matter left up to local jurisdictions.
Daylight saving time was observed nationally again during World War II, but was not uniformly practiced after the war's end.
Finally, in 1966, Congress passed the Uniform Time Act, which standardized the start and end dates for daylight saving time but allowed individual states to remain on standard time if their legislatures allowed it.
A 1972 amendment extended the option not to observe DST to areas lying in separate time zones but contained within the same state.
Before the move by Congress last year to extend DST, the most recent modification occurred in 1986, when the start date was moved from the last Sunday in April to the first Sunday in April.
According to Mosley, the drive behind the switch is "to adjust daylight hours to when most people are awake and about."
Daylight saving time decreases the amount of daylight in the morning hours so that more daylight is available during the evening.
Not everyone benefits from the change, Mosley conceded. Farmers and others who rise before dawn may have to operate in the dark a while longer before daybreak.
Daylight saving time, however, can bring many benefits. Mosley said research has shown that more available daylight increases energy savings while decreasing the number of traffic accidents, traffic fatalities, and incidences of crime.
Congress noted other advantages while updating legislation in 1986, including "more daylight outdoor playtime for the children and youth of our Nation, greater utilization of parks and recreation areas, expanded economic opportunity through extension of daylight hours to peak shopping hours and through extension of domestic office hours to periods of greater overlap with the European Economic Community."