Permanent daylight-saving time could add approximately 2.14 billion school commutes before sunrise annually across the US, exposing more children to conditions associated with greater pedestrian involvement in fatal traffic crashes.
Investigators conducted a modeling and observational analysis using school start times, enrollment records, and geographic information from 16,093 public schools serving approximately 8.6 million children across 14 US states that have enacted permanent daylight saving time legislation. They compared projected morning commutes under permanent daylight saving time (DST), permanent standard time (ST), and the current seasonal system. A separate analysis examined fatal motor vehicle crashes recorded in the National Highway Traffic Safety Administration's Fatality Analysis Reporting System from 2015 to 2024.
The primary outcome was the estimated number of school commutes occurring before sunrise under each clock system, expressed as child-days of exposure. Investigators used school start times, local sunrise times, and an assumed 20-minute commute to calculate exposure. Secondary analyses examined differences by school level and geographic location, as well as associations between morning darkness and pedestrian involvement in fatal crashes during school-year weekdays from 7 AM to 8:30 AM.
Across the 14 states, permanent DST was projected to add approximately 356 million dark-morning child-commute days annually compared with the current seasonal system. Estimated exposure increased from approximately 198 million child-days under the current system to 554 million under permanent DST, compared with approximately 97 million under permanent ST.
The projected increase occurred across all 14 states, although the magnitude varied by geographic position and school start time. Schools located farther west within their time zones generally experienced more dark-morning commutes because sunrise occurred later relative to the clock. Earlier school start times were also associated with more pre-sunrise departures.
In Washington state, permanent DST was projected to add approximately 28 dark-morning commute days per elementary school student and 39 days per high school student annually compared with the current system. In Seattle, where elementary schools started earlier than secondary schools, elementary students were projected to have approximately 58 total dark-morning commute days, compared with approximately 12 to 17 days for students at other school levels.
When the investigators extended the analysis to public schools nationwide, permanent DST was projected to add approximately 2.14 billion pre-sunrise commutes annually compared with the current system, assuming an 8 AM departure time for all students. Sensitivity analyses using departure times of 7:45 AM and 8:15 AM yielded estimates of approximately 2.63 billion and 1.39 billion additional child-days, respectively.
The national traffic safety analysis included 10,305 fatal crashes occurring during school-year weekday mornings, of which 1,754 involved pedestrians. After adjustment for clock hour and weather conditions, fatal crashes occurring before sunrise had 1.77 times the odds of involving a pedestrian compared with crashes occurring after sunrise.
Among pedestrians aged 5 to 18 years, the association was stronger. Fatal crashes occurring before sunrise had 2.22 times the adjusted odds of involving a pedestrian in this age group compared with crashes occurring after sunrise. The subgroup analysis included 141 pedestrian-involved fatal crashes.
The investigators noted that the current seasonal clock system already results in more dark-morning commutes than permanent ST. They also emphasized that permanent DST would extend later sunrise times into winter school months, increasing the number of days children would need to leave home before daylight.
The study had several limitations. Commute exposure estimates relied on assumed departure times rather than individual travel patterns, and the nationwide projection used a fixed departure time because school-specific schedules were unavailable nationally. The traffic safety analysis included only fatal crashes and did not capture nonfatal pedestrian incidents. Additionally, the observational and model-based analyses could not establish whether permanent DST would directly increase pedestrian injuries or fatalities.
“Altogether, adopting permanent DST would negatively impact youth sleep, health, and performance and, most critically, their safety,” wrote lead study author Guadalupe Rodríguez Ferrante, PhD of the Department of Biology at the University of Washington in Seattle, and colleagues.
The authors declared no competing interests.
Source: Current Biology
