It’s one of autumn’s iconic debates, up there with how early pumpkin spice lattes should go on sale and what the best Halloween candy is: Should we stop resetting our clocks twice a year — and if so, what time should rule?
People’s arguments surrounding daylight saving time often boil down to their personal preference, although scientists have gathered real evidence about what the twice-annual time change does to our bodies and what would happen if we stopped. Research published Thursday in Current Biology adds to that story by tallying how many children’s trips to school would occur before sunrise under each scenario. The researchers found that permanent daylight saving time would cause the highest number of dark commutes — about 2 billion more annually nationwide than under permanent standard time.
“It’s an important piece of the puzzle,” said Jamie Zeitzer, a professor at Stanford University who was not involved in the new research. “There are lots of changes that happen when you arrange what clock time the sun is rising, and this is definitely one of them.”
For co-author Horacio de la Iglesia, a biology professor at the University of Washington, the research stemmed from feeling like existing science on the topic didn’t resonate with policymakers and the public.
“There’s a lot of biological and clinical reasons why standard time is better than daylight saving time, but usually explaining those is quite complex,” de la Iglesia said.
The stakes increased in July, when the House of Representatives approved a bill that would make daylight saving time permanent.
“Once that happened, we were like, ‘This is really urgent,’” said co-author Guadalupe Rodríguez Ferrante, a biologist at the University of Washington. (The bill has stalled in the Senate.)
The researchers had already started the analysis, which focuses on 14 states stretching from Washington to Louisiana to Maine. The scientists included more than 16,000 schools, determining the attendance and starting time for each. Then, they assumed an average commute of 20 minutes. The school’s location told them when the sun rises each day of a school year under different time systems.
The results were striking: Under the current split calendar, these 14 states see nearly 200 million dark commutes annually. Year-round standard time would halve that, while permanent daylight saving time would see it increase 2½-fold. (A simplified calculation estimates a total of 2 billion additional dark commutes nationwide if daylight saving time reigned, although the researchers are still gathering the data to execute the more precise analysis at scale.)
The effect was strongest for high school students, who would see an average of 40 percent of their morning commutes occur in darkness under permanent daylight saving time. Students relying on school breakfasts, who typically need to arrive before their colleagues, would also see more predawn travel.
Those dark commutes have real-world consequences: The researchers note, for example, that fatal car crashes are more likely to include pedestrians and bicyclists before sunrise than after, making early start times a potential safety risk for children.
Unfortunately, the finding represents just one piece in the complex network of outcomes from any choice of time system. Studied holistically, there’s evidence for and against every timekeeping option. And realistically, Zeitzer said, most of us will end up experiencing only a very small effect, especially given the inconsistencies in any individual’s sleep patterns over time.
“Every day, people lose an hour of sleep, gain an hour of sleep, move that hour of sleep,” Zeitzer said. “But people get very upset when the government tells them to do it.”
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