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Daylight saving time started at 2 a.m. this morning in Pleasanton and across most of the country, with clocks forwarded by one hour, giving us more daylight in the evening, though a bit less in the mornings for the first few weeks.

Since 2007, daylight saving time starts on the second Sunday of March and ends on the first Sunday of November, with all time changes taking place at 2 a.m. local time. This year, Pacific Standard Time returns on Nov. 2, the first Sunday after Halloween.

It all goes back to World War I when, in an effort to conserve fuel, Germany began observing DST on May 1, 1916. As the war progressed, the rest of Europe adopted DST. The plan was not formally adopted in the U.S. 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, however, 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 Feb. 9, 1942. It lasted until the last Sunday in September 1945. The next year, many states and localities adopted summer DST.

From 1945 to 1966, there was no federal law regarding daylight saving time, so states and localities were free to choose whether to observe it, and could choose when it began and ended.

By 1962, the transportation industry found the lack of nationwide consistency in time observance confusing enough to push for federal regulation. This drive resulted in the Uniform Time Act of 1966.

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 a.m. on the last Sunday in April and turned back one hour at 2 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, 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 2012, 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 (OPEC), in an effort to conserve fuel, Congress enacted a trial period of year-round DST beginning Jan. 6, 1974, and ending April 27, 1975.

From the beginning, the trial was hotly debated. Those in favor pointed to the benefits of 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 to return to standard time for the period beginning Oct. 27, 1974, and ending Feb. 23, 1975, when DST resumed. When the trial ended in 1975, the country returned to observing summer DST with the previous exceptions).

DOT, charged with 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 this same data was compared between 1973 and 1974 for the individual months of March and April, no significant difference was found for 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 with the new and current starts and stops of daylight time imposed the following year, in 2007.

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