When the clocks go back, the walk home turns deadly

On 1 November most of America turned its clocks back an hour. Overnight the evening rush hour, which had been in daylight or dusk, moved into the dark. America's federal register of fatal crashes, kept since 1975, records every death on a public road with its date and hour. We counted the pedestrians killed in the three weeks before each autumn change and the three weeks after, hour by hour, for fifty years.

Between 5pm and 7pm the toll jumps the moment the clocks change. In the week before, 710 people were killed on foot at those hours, all fifty years added together. In the week after, 1,869 were, two and a half times as many, and the count stays there for the following weeks. Late at night, from 8pm to midnight, when it is dark either way, deaths do not rise; they fall slightly.

The police record the light at each crash. In the three weeks before the change, 46% of the pedestrians killed between 5pm and 7pm died in the dark. In the three weeks after, 88% did. In the past decade alone, about 125 people a year were killed on foot at those hours in the three weeks after the change, against 38 in the three weeks before.

A test the calendar set up

Part of that jump is the season: the days shorten through October and November whatever the clocks say. Arizona and Hawaii, which do not change their clocks (apart from the Navajo Nation in Arizona), show it. Their evening deaths rise too, against late-night deaths, by 1.8 times. Elsewhere the rise is 3.6 times.

A change of law separates the two. Until 2006 the clocks went back on the last Sunday of October. Since 2007 they go back on the first Sunday of November. The week in between kept light evenings under the new rule, on the same dates of the year. Under the old rule (1987-2006) an average of 35 people a year were killed on foot between 5pm and 7pm in that week. Under the new rule (2007-2024) it was 14. In the two weeks after, in standard time under both rules, the toll barely moved: 33 a week and 36.

The light was paid for in the morning. Under the new rule that week's mornings stayed dark for longer, and deaths between 6am and 8am more than doubled. But mornings kill far fewer people on foot to begin with: about 8 more deaths a year in the morning, against 33 fewer in the evening, once the rise in late-night deaths over the same years is allowed for. Net, the later change saves about 25 lives a year (our range: 16 to 34).

Both ways, every time

The pattern holds wherever the light moves. After the autumn change, mornings brighten and morning deaths fall by about two-fifths. After the spring change, evenings brighten and evening deaths fall by more than half, while darker mornings bring a third more deaths. The researchers Michael Sullivan and Michael Flannagan used the same clock changes in 2002 to measure how much more dangerous darkness is for people on foot. Twenty more years of records point the same way, and the evening rise has been larger since 2000 than before it.

Congress has argued for years about ending the change, and the Senate voted in 2022 to make daylight saving time permanent. The register cannot settle that argument: it counts deaths, not how many people walk at each hour. It does show where the danger lies now. In November to February, the hour from 6pm is the deadliest of the day for people on foot, with almost three and a half times the deaths of the worst morning hour. Until the rules change, the next few weeks are the time to wear something bright on the walk home, and to drive as if someone is out there.