Fighting crime with Daylight Saving Time

On a seemingly-arbitrary Sunday each spring and fall, we all dutifully change our clocks by an hour, often griping about the hassle. Sometimes we do this only after missing an appointment, making the transition even worse. Even in a modern world where electronic devices update time for us, the shift of an hour messes with sleep patterns and daily routines – anyone with kids can tell you babies don’t respect Daylight Saving Time (DST). Why even bother with the shift anymore? What’s the point of moving an hour of sunlight into the evening?

In a new paper forthcoming in The Review of Economics and Statistics, we find that shifting daylight from the morning to the early evening has pretty hefty returns for public safety. When DST begins in the spring, robbery rates for the entire day fall an average of 7 percent, with a much larger 27 percent drop during the evening hour that gained some extra sunlight.

Why might this time shift matter? The timing of sunset is pretty close to the time many of us leave work, and walking to our cars or homes in the dark makes us easier targets for street criminals. We feel safer when we’re walking in the daylight, and it’s easy to imagine why light might have a deterrent effect on crime: offenders know they’re more likely to be recognized and get caught if they’re fully visible. The timing of sunset matters because our daily schedules can’t easily adapt to follow the daylight. Most people can’t leave work before 5pm, even if it would be safer to do so.

Congress occasionally extends DST, often with the stated goal of reducing energy consumption. In 2007 it extended the policy by four weeks – three in the spring and one in the fall. This produced a useful natural experiment for our paper, which helped us isolate the effect of daylight from other seasonal factors that might affect crime. It turns out extending DST saved $59 million per year in avoided social costs by reducing the number of evening robberies. Even better, robbery rates didn’t increase in the morning, even though those hours were darker – apparently, criminals aren’t early risers.

Does this mean we should extend DST further? It’s complicated. There’s research showing DST does not, in fact, reduce energy consumption. And other researchers find that the DST time shift has substantial costs, including reducing our response time and cognition, and adding extra stress on our bodies. It increases the number of traffic accidents, workplace injuries, and heart attacks in the days just after the time change, as our internal clocks are thrown off. But most of these costs are due to the transition between Standard Time and DST, not the sunset time itself. We could easily avoid them by moving to year-round DST – that is, permanently shifting that hour of daylight to the evening, and then leaving our clocks alone. Our research suggests that we’d be safer for it.