On March 19, 1918, the US Congress passed the Standard Time Act, which divided the continental US and Alaska into five time zones. Congress delegated authority to the International Commerce Commission (ICC) to define the boundaries of these time zones for the benefit of interstate commerce carriers. Prior to the act, the railroads had defined time zones for more efficient interstate travel. The act also established daylight savings time in a provision that was repealed in 1919. Congress reestablished daylight savings time in 1942 for the duration of World War II, and later made the measure permanent with the Uniform Time Act of 1966.
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