MOUNT VERNON — As the leaves fall in fall, it’s time to fall back an hour on the clock Saturday night/Sunday morning as daylight-saving time comes to an end for 2009. Though many parts of the United States are in the 91st year of observing the time-tweaking practice, it has only been federally mandated for about five of those years: First, in 1919, until the federal mandate was overturned, and, second, during World War II. Otherwise, it’s a state decision, with the national government setting only the dates.

Those dates are set by the Department of Transportation. While this might seem odd at first glance, time has a long history of being a transportation issue in the U. S. In the early to mid 1800s, local time was set in every community, and varied wildly. Once the nation became linked by railroads, time variances became not only a matter of confusion, they could even result in train wrecks. To establish uniformity, the railroads banded together and established the four time zones, Eastern, Central, Mountain and Pacific. This worked so well, the U.S. Congress made the time zones the official law of the land in 1918.

At the same time, it was decided to push the idea of daylight-saving time, which had first been proposed in 1784 by Benjamin Franklin. The idea was that by tweaking the clock, an additional hour of daylight could be had in the evening in summertime, when the public could enjoy it most, though early-rising farmers might grumble about starting work in the dark.

The reason daylight-saving time was made mandatory during World War II was the energy savings from giving the public an extra hour to be outdoors in the evening. Today, that reason no longer holds true, as energy-consuming activities are likely to occupy that hour. But according to studies by the U.S. Department of Transportation, the number of evening car/pedestrian accidents goes down during the extended daylight, saving lives. Retailers also welcome the extra daylight, which encourages shoppers to stay out.

These latter benefits of daylight-saving time have picked up weight in recent years, leading to a decision by Congress in the Energy Policy Act of 2005 to extend the practice. Since 2007, daylight-savings time has started the second Sunday in March, and ended the first Sunday in November.

Though daylight-saving time remains controversial, there are no indications that it will be abandoned at this point.