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South Dakota’s Round-the-Clock Debate Over Daylight Saving Time

SIOUX FALLS, S.D. — Love “Daylight Saving Time” or hate it, a new study shows the annual transition boosts traffic accidents due to sleep deprivation and disturbed circadian rhythm. South Dakota lawmakers considered a bill this session to permanently move the clock ahead — legislation also introduced in 2015 and 2016.

Ken Wright, director of the University of Colorado’s Sleep and Chronobiology Laboratory, said we’ve been adjusting the clock for 100 years and humans adapt each time. But no matter when the switch occurs, he said, it always increases the short-term risk of car crashes.

“So when the switch occurred and we started in March 2007 onward,” he said, “the increased risk moved to March instead of staying where it was in April, for example.”

It’s estimated that traffic accidents increase by about 17% in the first week of the change to daylight saving. DST was adopted in 1918 to conserve oil, wax and coal during World War I. This year, the United States will “spring forward” on Sunday, March 8, and “fall back” to standard time on Sunday, Nov. 1.

President Donald Trump has said he’s in favor of permanent daylight saving time, but opponents have argued it would mean students waiting outside for buses in the coldest, darkest time of the morning. For Wright, it’s more about the body clock. He said circadian misalignment makes people sluggish, and fatal motor-vehicle accidents are known to increase by 6%.

“Your reaction times are slower, different parts of your brain that are important for keeping track of your environment aren’t as effective, and decision-making making is slower and impaired,” he said. “And so, we know that that acute change is increasing the risk of bad things happening.”

He said the number of traffic accidents returns to normal a week after the time change occurs.

Federal law allows states to remain permanently on standard time, but prohibits remaining on daylight saving time without congressional approval. Seven states have passed legislation to remain on it should Congress approve such a measure, including Nevada, Oregon and Washington.

The text of the legislation, House Bill 1085, is online at The study is at


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