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U.S. Department of Transportation U.S. Department of Transportation Icon United States Department of Transportation United States Department of Transportation

History of Time Zones

Sunday, February 21, 2021

With the 2019 Fall release of the National Transportation Atlas Database (NTAD), a new map of the nation’s time zones is featured, showing the geographical boundaries of four time zones in the continental U.S. and the five additional time zones used in Alaska, Hawaii and other U.S. territories.1,10 These time zones, with boundaries that have for the most part been fixed for more than a century, are taken for granted by most Americans. But that has not always been the case.

Before the establishment of time zones in 1883, there were over 144 local times in North America.3 The resulting small time differences between adjacent towns and cities were not critical when it took days to travel from place to place.2 With the proliferation of railroads, faster travel became possible across many cities and travelers could sometimes arrive at an earlier local time than the one they had left.2 Due to this lack of time standardization, schedules on the same tracks often could not be coordinated, resulting in collisions.3 The major railroad companies as a result began to operate on a coordinated system of four time zones starting in 1883.2

Standard time was transportation-driven and, as a result, the government coordination of time zones was handled by transportation agencies.5 The federal organization in charge of railroad regulation – the Interstate Commerce Commission – was given the power to address coordination concerns in 1918.1,5 That year, five time zones were officially adopted as the US entered World War I: the Eastern, Central, Mountain, Pacific, and Alaskan zones still in use today.1 However, the need for coordination among all modes, became increasingly important after World War II.4 When the Department of Transportation was founded in 1966, the responsibility of regulating standardized time was transferred to it.1,4

Daylight Savings Time (DST) is another responsibility of the Department of Transportation and has since become integral to the workings of modern society.10 While the adoption of standard time was motivated by transportation improvement, DST has become more widespread for reasons of energy savings and economy.7

Today, the Department of Transportation continues to supervise standard time due to its historical and contemporary importance in transportation and associated commercial activity.10 DST is observed uniformly across the nation with the exception of four territories and two states (Arizona and Hawaii).7 Time zone boundaries are also established by law and can only be changed by the Secretary of Transportation if the adjustment is deemed to benefit commerce.8 Over the past two decades, 15 communities (counties, cities, and parts of counties) have changed their time zone boundary, the most recent being Mercer County, North Dakota.9 It switched from Mountain to Central Time in 2010.9 The new map in the 2019 Fall NTAD release includes these changes and showcases the most up-to-date information on standard time zones in the nation.  


1. Clark, Corrie E., and Lynn J. Cunningham. 2018. Daylight Saving Time. CRS Reports (Library of Congress. Congressional Research Service). Available at as of October 2019.

2. Gordon, John Steele. Standard Time: We All Live By What Happened on November 18, 1883. American Heritage, Jul./Aug. 2001, pp. 22-23.

3. Phillips, Charles. A Day To Remember: November 18, 1883. American History, Dec. 2004, pp. 16-18.

4. United States. 1966. Creating a Department of Transportation: Hearings before a Subcommittee of the Committee on Government Operations, House of Representatives, 89th Congress, 2nd session, on H.R. 13200 a bill to establish a Department of Transportation and for other purposes. Washington, DC: U.S. GPO.

5. United States. 1966. Department of transportation act: report to accompany H.R. 15963. Washington, DC: U.S. GPO.

6. United States. 1966. Establish a Department of Transportation: Hearings, 89th Congress, 2nd session, on S. 3010, a bill to establish a Department of Transportation, and for other purposes. Washington, DC: U.S. GPO.

7. U.S. Department of Transportation. Daylight Savings Time (3/10/2014). Available at as of October 2019.

8. U.S. Department of Transportation. Procedure for Moving an Area from One Time Zone to Another (4/30/2013). Available at as of October 2019.

9. U.S. Department of Transportation. Recent Time Zone Proceedings (6/06/2012). Available at as of October 2019.

10. U.S. Department of Transportation. Uniform Time (2/13/2015). Available at as of October 2019.