Daylight saving time (DST) ends today. Most Americans will set back their clocks and gain an extra hour of sleep, just as they have since the mid-1960s. Some nations rely on DST to add an extra hour of early-morning sunlight, while others never touch their clocks at all.

Americans have a love-hate relationship with DST. Farmers hate DST because it affects their “early rise” work patterns. Parents complain that DST creates safety concerns, with children heading off to school in the artificially dark morning. But merchants typically like DST because an extra hour of daylight in the evening can be good for business.

So why not make DST last year-round? Or get rid of it altogether? In new research, we show that local politics — more so than party and ideology — shape lawmakers’ positions on DST. As historical opponents of DST decline in importance, pressure for year-round DST is growing and could lead Congress to act.

Here’s what you need to know.

1. Wartime demands gave rise to the idea of DST

The origins of DST lie in World War I. European leaders saw DST — wherein time would be advanced in April and then reversed in September — as a way to save energy by reducing lighting costs. In 1916, Germany and Britain became the first nations to adopt DST. The United States followed suit two years later, including DST in legislation that standardized the country’s time zones.

From the start, farmers opposed DST, while businesses were in favor. After the war, farmers built up lobbying organizations in Washington and sought to use their influence to roll back DST. Without the wartime concern for saving energy, organized farming interests won out, and Congress repealed DST in August 1919 over President Woodrow Wilson’s veto.

Congress temporarily reinstated DST during World War II. But afterward, cities, counties and states pursued whatever time policy they preferred. This could be confusing. In 1955, for example, a trucker driving goods from Atlanta to Boston might have to recalculate the actual time repeatedly while passing through different time regimes — without ever leaving the Eastern time zone.

By 1965, DST was operating fully in 15 states and in parts of 16 others. The communications and transportation industries had had enough of this decentralized system, and executives lobbied Congress for a new national standard. In April 1966, Congress instituted DST for six months of the year.

2. America has had DST since 1966 — with some tweaks

Since 1966, the provisions of DST have changed. The OPEC oil embargo of 1973-1974 led the United States to experiment with “permanent” DST. Public opinion began to shift against DST, however. Many parents were upset when their children had to leave for school in the dark. When several children were killed in traffic accidents early in the winter of 1973-1974, critics blamed DST. After the embargo ended, Congress returned to the limited DST policy of the Johnson administration.

In 1987 and 2005, business interests — convenience stores, fast-food companies, makers of barbecue grills and candy manufacturers — successfully lobbied for the expansion of DST. The 2005 extension took DST into November, providing one more hour of daylight for children to go trick-or-treating on Halloween.

3. Here’s how we did our research

So what do we know about the coalitions that formed around proposed DST changes? We studied congressional voting since World War I — we started by collecting every House and Senate roll call vote from 1918 to the present that specifically targeted DST. We located 21 such votes. For each vote, we coded whether each member voted to expand or contract the total number of hours of observed DST.

Then, we determined the party and ideological orientation for each member of Congress in our data set and included a variable to capture the farmers’ share of the population in each congressional district.

We measured parental interests indirectly. DST opponents argue that pushing time forward could mean predawn commutes for workers and schoolchildren, increasing risks of accidents. If this were true, the Western portions of each time zone would be the ones most likely affected. We thus used the distance between the geographic center of each district and its Western time zone barrier to assess just how strong DST’s effects were in each district or state.

4. We found that politics are indeed local

Conservatives (and Republicans) have been more resistant to expanding DST than liberals (and Democrats). This may seem surprising given the business community’s support for DST. But conservatives’ opposition probably stems from a broader aversion to government intrusion into something as fundamental as the time of day.

Lawmakers also pay close attention to local special interests when voting on changes to DST. Specifically, the greater the proportion of farmers in a district, the stronger their representatives’ opposition to DST in Congress. Members closer to the western border of their specific time zone — where DST pushed sunrise much later into their day and thus increased morning darkness and potentially accident risks — were less supportive than those farther away from the western edge.

Overall, party and ideology are important influences on lawmakers’ votes on DST — but our findings suggest local forces were more salient in shaping the DST voting.

5. Could attitudes on DST be changing?

The United States, of course, has become less agrarian, so farming interests are declining in power, putting less pressure on Congress over DST. And business interests remain strongly in favor of DST.

Meanwhile, efforts are growing in the states. So far in 2019, 40 states have introduced legislation addressing DST. Most of these measures seek to move to year-round DST. In Congress, Sen. Marco Rubio (R-Fla.) has introduced a bill to do the same at the federal level.

But revisions to federal law are necessary to make DST year-round because states must adhere to the federal standard for DST. Will this bottom-up pressure lead Congress — gridlocked on so many issues — to act?

Only time will tell — pun intended! — whether year-round DST is an idea whose time has come.

Thomas R. Gray is an assistant professor of political science in the School of Economic, Political and Policy Science at the University of Texas at Dallas.

Jeffery A. Jenkins is a provost professor of public policy, political science and law; Judith and John Bedrosian Chair of Governance and the Public Enterprise; director of the Bedrosian Center; and director of the Political Institutions and Political Economy (PIPE) Collaborative at the Sol Price School of Public Policy at the University of Southern California.