Oct 12, 2018 4 min read

We’re all highly aware of the dangers posed by drunken drivers and by motorists tapping away or talking on their cellphones, but there’s another group of hazardous drivers out there: those who haven’t had enough sleep.

According to a new study by the AAA Foundation for Traffic Safety in Washington, D.C., people who drive after getting less than four hours of sleep are every bit as likely, perhaps even more likely, to get into an accident as drivers who have had too much to drink.

The foundation’s senior researcher, Brian Tefft, told Reuters Health that the study was based on a review of data from nearly 7,000 vehicle accidents between 2005 and 2007. Drivers involved in those wrecks already had been interviewed in depth by federal Department of Transportation investigators.

“The sharp increase in risk below four hours (of sleep) stands out,” said Dr. Sanjay Patel of the University of Pittsburgh, who was not involved in the study.

“The odds of being responsible for a crash go up from 2.9-fold to 15.1-fold as sleep drops from about four to five hours to less than four hours,” Patel told Reuters. “But that … is not surprising given what we know about how decreasing sleep affects other aspects of brain function.”

Tefft said in his report that drivers who had slept less than four hours had “crash risks” similar to someone with a blood-alcohol content of 0.12 percent, which is 50 percent higher than the level at which intoxication is presumed in adult, noncommercial drivers.

Simply not getting enough sleep wasn’t the only risk identified by the study. The researchers found that drivers who had experienced recent changes in their sleep or work schedules had about a 30 percent increase in their risk of causing an accident, Reuters reported.

The study also noted that drivers who slept less than four hours over a 24-hour period were at a much higher risk of being involved in a single-vehicle crash. Interestingly, Tefft told Reuters that single-vehicle wrecks are more than three times as likely as multi-vehicle accidents to result in fatalities.

The Reuters report cited data from the National Sleep Foundation indicating that “sleepy driving” is fairly common, with 60 percent of U.S. adults saying they had driven while feeling drowsy and one-third saying they had actually fallen asleep while driving.

But Benjamin McManus, a researcher at the University of Alabama’s Translational Research and Injury Prevention Laboratory, told Reuters that the sleep-deprivation crashes studied by Tefft aren’t all cases of people “nodding off” or being asleep at the wheel.

“Judgment and decision-making are highly impacted by poor sleep quantity and quality,” McManus said. “With changes in the work economy and growth of ride sharing, we’re seeing a growth of a ‘gig’ economy where many work from home, work irregular hours, or work multiple jobs. (Data like this) may make the difference between recommendations of ‘you need a cup of coffee’ versus ‘you need a nap.'”

There are going to be times, no doubt, when all of us have to drive without having had the optimum amount of sleep, but clearly it’s something that should be avoided if at all possible.

And that still goes for people who insist on using their cellphones while behind the wheel. We’ve said it before, and we’ll say it again: Even just talking on your cellphone while driving, whether it’s a hand-held or hands-free conversation, puts you and other people at risk. There are few calls that can’t wait until you can pull off the road or get to your destination.