Keeping daylight saving time year-round would bring brighter winter evenings, but it could also mean many more children traveling to school before sunrise, according to research from the University of Washington. The researchers estimate the change could add at least 2 billion dark school commutes nationwide compared with the current system of switching clocks twice a year.

The study examined school enrollment, start times and locations in 14 of the 19 states that have approved measures supporting permanent daylight saving time. In Washington state, the change would add nearly 35 million school trips in darkness, while Georgia would see the largest increase among the states studied, at about 71 million.

Researchers also analyzed U.S. traffic collision records and found fatal crashes involving school-aged pedestrians were roughly twice as likely during dark mornings as after sunrise. The findings were published October 29 in Current Biology.

Permanent daylight saving time would shift winter sunrise an hour later, leaving mornings darker from November through March. The researchers say reduced access to morning sunlight could also affect children’s circadian rhythms, which help regulate sleep and other bodily functions.

The impact would vary by location and school schedule. Schools near the western edges of time zones, where sunrise is already later, and districts with early start times could face larger increases. In Mississippi and Alabama, where schools begin on average before 8 a.m., the researchers estimate dark school trips would rise from about 2 million to more than 20 million per state.

The nationwide estimate may be conservative. To calculate it, the team assumed students generally leave for school around 8 a.m., although many travel earlier. The researchers said that assumption could mean the actual increase is higher.

The study comes amid debate over ending seasonal clock changes. The U.S. House of Representatives approved legislation this past summer to keep daylight saving time in place year-round, but the proposal remains stalled in the Senate. The researchers say delaying school start times could address darker commutes, but would also affect families and work schedules.

Sources: ScienceDaily.