As Americans turned their clocks back an hour, a new study is sharpening the debate over whether seasonal time changes should continue. The research suggests that making Daylight Saving Time permanent could expose millions of children to darker and potentially more dangerous school commutes.

The study, published Thursday in Current Biology, examined school start times at more than 16,000 schools across 14 states. Those schools represented approximately 8.6 million children, according to researchers from the University of Washington.

CNN wellness expert Dr. Leana Wen, an emergency physician and clinical associate professor at George Washington University, discussed the findings and the approaching time change. Wen previously served as Baltimore’s health commissioner and is the mother of two young children.

When Daylight Saving Time ends November 1, clocks move backward from 2 a.m. to 1 a.m. Sunrise and sunset then occur an hour earlier by the clock, providing more morning daylight while bringing darkness earlier in the evening.

The United States currently begins Daylight Saving Time on the second Sunday in March and ends it on the first Sunday in November. The twice yearly changes remain controversial because they can disrupt sleep schedules, established routines and daily activities.

The spring change is often especially difficult because people lose an hour of sleep. Although the fall change provides an additional hour, Wen said it can still disturb sleep, particularly among young children with established bedtime and wake up routines.

Supporters of permanent Daylight Saving Time argue that people would no longer need to change their clocks twice each year. They also favor additional evening daylight for outdoor exercise, recreation and certain businesses, while some research suggests it could reduce some traffic accidents.

The Sunshine Protection Act, passed by the US House of Representatives in July, proposes making Daylight Saving Time permanent nationwide. Under that proposal, Americans would retain evening daylight during winter, but winter sunrise would occur an hour later.

Researchers calculated how often children would leave home before sunrise under permanent standard time, the current clock changing system and permanent Daylight Saving Time. They estimated permanent Daylight Saving Time would create approximately 356 million additional school commutes before sunrise each year across the 14 states.

When the analysis was extended nationwide, the estimate exceeded 2 billion additional dark morning school commutes annually. The nationwide calculation assumed an 8 a.m. school start time, even though school schedules vary and many schools begin later.

The researchers also analyzed nationwide fatal motor vehicle crashes recorded from 2015 through 2024. Their review focused on more than 10,000 fatal crashes that occurred on school year mornings between 7 a.m. and 8:30 a.m.

Crashes before sunrise had 77% higher odds of involving a pedestrian than crashes after sunrise. Among children ages 5 to 18, the odds of pedestrian involvement were more than twice as high during dark mornings.

Visibility is a central concern because drivers can have greater difficulty seeing pedestrians in darkness, particularly smaller children. Younger children are also still developing their ability to assess vehicle speed and distance, while teenagers driving to school have limited driving experience.

The study did not experimentally change clock policies and then measure crashes. Instead, researchers used existing school schedules, sunrise calculations and historical crash records to estimate possible effects, meaning policymakers must consider the study’s design when evaluating its findings.

Children from families with lower incomes could face disproportionate effects, the researchers noted. Some travel earlier to attend school breakfast programs and may be more likely to depend on walking or public transportation.

Permanent standard time would preserve more daylight during morning trips to school and work. Several medical organizations, including sleep medicine specialists, favor that approach because morning sunlight helps align schedules with circadian rhythms, which regulate sleep, alertness and other physiological functions.

Families can prepare for the clock change by gradually moving children’s bedtimes, meals and evening routines about 15 minutes later each day for four days. Consistent wake up times, morning natural light, outdoor activity and predictable evening routines can also support healthy sleep.

Earlier sunsets bring additional safety concerns for children walking or cycling home from school or afternoon activities. Wen advised reflective clothing, bicycle lights, marked crossings and, when possible, traveling with an adult or a group of friends.