Time zones were first adopted by the United States Congress with the Standard Time Act of 1918. All of Indiana was located in the central time zone. It was at this time that the dividing line between Eastern Time and Central Time moved from the Pennsylvania-Ohio border to the Indiana—Ohio border. In the late 1940s, the use of daylight saving time, known as fast time, became popular in cities. Indiana is officially in the central time zone, but some communities choose to follow fast time throughout the year, essentially aligning themselves with the Eastern time zone.