Darker Mornings: The Hidden Cost of Permanent Daylight Saving Time
ATwice a year, people in most of the United States change their clocks. In spring the clocks move forward by an hour, shifting daylight from the morning into the evening, and in autumn they move back again, returning to what is known as standard time. Many people find the switch tiresome, and there has been growing support for ending it altogether. One proposal is to remain on daylight saving time all year round, which would give people an extra hour of light on winter evenings. A new study from the University of Washington, however, suggests that this extra evening light would come at a considerable price for schoolchildren.
BThe reason is a matter of simple arithmetic. Under permanent daylight saving time, the sun would rise an hour later by the clock than it does now during the winter months. From November to March, therefore, mornings would stay dark for longer. For children who have to be at school early, this means that a much larger share of their journeys would begin before sunrise. The question the researchers set out to answer was exactly how many additional journeys would be affected.
CRather than relying on rough national averages, the team, led by postdoctoral researcher Guadalupe Rodríguez Ferrante, wanted figures that reflected where children actually go to school. They focused on 14 of the 19 states that have already approved measures supporting permanent daylight saving time. For each school, they combined enrolment figures with the school's official start time and its precise geographical position. This allowed them to work out how often pupils would be travelling before sunrise, and to compare the total under year-round daylight saving time with the total under the present system of changing the clocks twice a year. Because they used official start times, the researchers point out that their figures may be conservative, since pupils who arrive early for breakfast or other activities before lessons leave home even earlier.
DThe results were striking. In Washington state alone, the change would add almost 35 million school journeys made in darkness. The largest increase among the states studied was in Georgia, with around 71 million extra dark trips. In some states, the relative change would be dramatic. In Mississippi and Alabama, where schools begin on average before 8 a.m., there are currently about 2 million dark school journeys in each state, but under permanent daylight saving time this number would rise to more than 20 million in each. Location within a time zone also matters: communities near the western edge of a zone, such as the town of Forks in Washington, already have a late sunrise and would be especially badly affected. Some districts where pupils never travel in the dark at present would also begin to experience dark journeys to school.
EThe researchers then extended their analysis to the country as a whole. Assuming that pupils generally leave home at around 8 a.m., they estimated that permanent daylight saving time would add well over a billion journeys to school before sunrise nationwide. They regard this departure time as rather late, which means that the true figure is probably higher. They also examined national traffic records and found that fatal road accidents involving pedestrians of school age were roughly twice as likely on dark mornings as after the sun had risen.
FSafety on the roads is not the only concern. Bright light early in the day plays a key role in setting the body's internal, or circadian, clock, which influences sleep, mood, appetite and many other functions. Pupils who must follow a fixed school timetable may miss the morning light that their bodies rely on, particularly when mornings are dark. Teenagers are a special case, because their biological clocks naturally run later than those of younger children and adults. Later start times for high schools are often recommended for this reason, but the researchers argue that permanent daylight saving time could undo some of their benefit by reducing the amount of morning light that teenagers receive.
GAn obvious response would be simply to start school later in winter. Senior author Horacio de la Iglesia, a professor of biology, argues that this would not solve the problem. If schools opened later, he points out, working hours and evening activities would soon move later as well. Society as a whole would then be living according to the sun rather than the clock, which is essentially what standard time already provides. People would therefore lose the extra evening light that was the main attraction of the change in the first place. For de la Iglesia, the conclusion is clear: the additional hour of evening sunshine is not a gift but a transfer, taken directly from the morning.