Permanent daylight saving time means darker morning school commutes

The U.S. House of Representatives passed a bill this past summer that would make Daylight Saving Time (DST) permanent in the United States - meaning there would be no turning back the clocks each fall. Nineteen states, including Washington, have already preapproved this change. If the bill is ultimately signed into law, the change would go into effect in those states.

The bill is currently stalled in the U.S. Senate. School start times are a central issue because permanent DST would lead to darker mornings from November to March. This would mean darker commutes for everyone, but how much would it affect children going to school? University of Washington researchers did the math for 14 out of the 19 states that preapproved the change. Using school start times, enrollment data, and latitude and longitude measurements, the team calculated just how many days each child would be commuting to school in the dark and then added the trips together.

In Washington, there would be almost 35 million more trips to school in the dark under permanent DST compared to the current system of switching between DST and Standard Time twice a year. The other 13 states followed a similar trend, with Georgia having the highest deviation from the current system - 71 million more trips. When the researchers extrapolated these results for the rest of the country, it added at least 2 billion more dark commutes to school.

The team also analyzed traffic collision data from the U.S. and found that it was roughly twice as likely for a fatal crash involving a school-aged pedestrian to occur during dark mornings than after sunrise.

The researchers published these results Oct. 29 in Current Biology.

It's called the 'Sunshine Protection Act' because you get an extra hour of light at the end of the day. But you will take that hour from the morning. You could call it the Sunshine Destruction Act. These dark mornings will inequitably affect children who have to go to school at a certain time. It's a very tangible metric that anybody from any state or socioeconomic background can relate to. Nobody wants their kids to go to school in the dark."

Horacio de la Iglesia, senior author, UW professor of biology

Dark mornings affect everyone. Exposure to bright light in the morning helps set our circadian clock, which helps regulate many facets of our lives, such as our mood, sleep and appetite. Without that morning light, our bodies struggle to regulate these key functions.

"When we send kids to school in the dark, we are depriving them from an opportunity to get that morning daylight," said lead author Guadalupe Rodríguez Ferrante, a UW postdoctoral scholar in biology. "We were asking what's the cost for these children. We wanted actual numbers, a real number of kids based on the geographic location of each school." 

The study revealed the areas that would be the hardest hit by the switch: communities on the western edge of their time zones, such as Forks, Washington, and communities with early school start times. For example, Mississippi and Alabama schools have an average start time of earlier than 8 a.m. and both balloon from about 2 million dark trips for each state under the current system to more than 20 million dark trips for each state under permanent DST.

"Some districts probably never experience a dark commute under the current system, and, if this passes, suddenly they will wake up to this new reality that their kids are going to school in the dark," Rodríguez Ferrante said. "Keep in mind that we used the actual start time listed for each school, and a lot of schools offer breakfast or other things before school, so the kids could be getting there even earlier."

After calculating real numbers for 14 states, the researchers estimated the total change in dark commutes if the whole country shifted to permanent DST. It adds up to about 2 billion more trips than under the current system.

"For the estimation, we assumed students would be leaving home around 8 a.m.," Rodríguez Ferrante said. "That's pretty late, so our calculation is likely an underestimation of the real number."

The researchers argue that permanent DST would also undo the benefits of having a delayed start time for high school students, which is intended to account for teenagers' shifted circadian clock compared to kids and adults.

"I've heard the argument, 'If we're in permanent DST, we can just delay the school start time to address these issues,'" de la Iglesia said. "Well, if we do that, you will end up going to work later. And everything is going to get delayed. You will get out of work an hour later, and you will miss the opportunity to enjoy your evening light. And essentially, we're just going to be realigning everybody to solar time. That, by definition, is Standard Time."