What is Daylight Saving Time and why does most of Arizona not observe it?

Starting this upcoming Sunday, March 14 at 2 a.m., approximately 70 million countries will move their clocks forward in observation of daylight saving time. 

While the vast majority of the United States will participate, there are some exceptions. According to the Congressional Research Service, the states and U.S. territories that do not observe daylight saving time include American Samoa, most of Arizona, Guam, Hawaii, the Northern Mariana Islands, Puerto Rico and the Virgin Islands. 


Daylight saving time in the United States was established by Congress under the Standard Time Act of 1918 as a “way of conserving fuel needed for war industries and of extending the working day,” according to the Library of Congress.

It was repealed following the end of World War I, however the issue reemerged during World War II and Congress established it yet again in 1942. In 1966, Congress established the Uniform Time Act to clarify issues surrounding the consistency with time observances under daylight saving. The rule allowed a state to exempt itself, or parts of the state that lie within a different time zone, from DST observance. In addition, the law authorized the Department of Transportation to regulate standard time zone boundaries and DST

The time period for DST was extended by four weeks through the Energy Policy Act of 2005. The rule, which was implemented in 2007, changed the start of DST to the second Sunday in March and end of the first Sunday in November. 


According to Timeanddate.com, most of Arizona does not set the clocks forward an hour for DST, with the exception of the Navajo Nation, who set the clock forward one hour to Mountain Daylight Time. Instead, Phoenix and most of Arizona observe Mountain Standard Time.

While most of Arizona currently doesn’t use DST, it was used by the state from March 31 to Oct. 27, 1918, along with the rest of the world during World War I and again during World War II after it was reenacted by President Franklin D. Roosevelt on Feb. 9, 1942. 

During the War Time period, Phoenix and most of Arizona added 1 hour to Mountain Standard Time to what is now known as Mountain Daylight Time. When the War Time period ended most of Arizona, including Phoenix, returned to MST.

Meanwhile, the communities along the state’s western border added 1 hour to Pacific Standard Time and used what is known today as Pacific Daylight Time. Following the War Time period, these locations returned to PST again.

On Jan. 1, 1944, when most of Arizona returned to MST, the western border communities remained on Pacific War Time, while railroads, airlines, bus lines, military personnel and interstate commerce continued to use Mountain War Time in line with federal law.

Three months later, an emergency law was passed to establish Mountain Time and Pacific Time as the state’s time zones. The law stated that DST was to be used from April 1 to Sept. 30. Federal offices and departments were exempt from the law. 

On Oct. 1, 1944, most of Arizona returned to Mountain Standard Time and stayed that way until the mid-1960s, while most of the Mohave County region changed to Pacific Standard Time. 

Arizona exempted itself from observing DST in 1968, according to the Congressional Research Service. Timeanddate notes that DST is “largely unncessary” due to Arizona’s hot climate and that the argument against extending the daylight hours is that people prefer to do their activities in cooler evening temperatures. 

The only other state that does not observe daylight saving time is Hawaii, which exempted itself in 1967.


While Congress is the only entity that can change the length of DST observance, at least 45 states have proposed legislation since 2015 asking to either be exempted from DST or to establish permanent DST. Most of the proposals have not passed.

The 11 states that have enacted permanent DST legislation are Delaware, Florida, Idaho, Louisiana, Maine, Oregon, South Carolina, Utah, Tennessee, Washington and Wyoming. In addition, Arkansas and Georgia have adopted resolutions in support of permanent DST.

On Tuesday, a bipartisan group of senators reintroduced the Sunshine Protection Act, a bill that would make daylight saving time permanent across the country. The senators include Marco Rubio, R-Fla, James Lankford, R-Oka., Roy Blunt, R-Mo., Sheldon Whitehouse, D-R.I., Ron Wyden, D-Ore., Cindy Hyde-Smith, R-Miss., Rick Scott, R-Fla., and Ed Markey, D-Mass. 

A 2011 study by the American Journal of Public Health found an estimated 901 fewer fatal car crashes during daylight savings time, including 727 involving pedestrians and 174 involving vehicle occupants.

In addition, research published in the European Review, National Library of Medicine and by the Mayo clinic found daylight savings helped reduce risk of cardiac issues, stroke and seasonal depression and studies published by the International Journal Behavioral Nutrition and Physical Activity and the Journal of Physical Activity and Health found an increase in children’s physical activity during DST.

A 2015 Brookings Institution study found that robberies during daylight saving times were reduced by 27% and a study by JPMorgan Chase found that daylight savings time benefits the economy, noting a drop in economic activity of 2.2% to 4.9 when clocks move back. 

Daylight saving time will end on Sunday, Nov. 7, 2021, when Americans will fall back an hour. 

Fox News’ Louis Casiano contributed to this report

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