The Department of Transportation governs US time..
Sometime in the '70s, Scientific American ran an article attributing the advent of standard time to the railways in order to make scheduling more like possible. Up until that then, the time in any given place was the local mean time and was measured from the sun's zenith, or high noon.
During the energy crisis following the oil embargo in '73, the federal government mandated that the entire country would stay on daylight savings time in order to -- conserve lamp oil (according to Henry Kissinger, the strategy of conservation was instrumental in breaking the back of the OPEC cartel). The mandate was ended when the outcry of irrate mothers reached Washington: they were concerned for their children's safety on their way to school.
