According to new research from the AAA Foundation for Traffic Safety, tired drivers are responsible for nearly one out of every 10 auto crashes. The risk is even higher during nighttime hours.

The researchers monitored 3,500 individuals in six locations across the U.S. between October 2010 and December 2013. Over that period, the drivers were involved in more than 700 crashes, with drowsiness a factor in 8.8% to 9.5% of them. More than 10% of the accidents that resulted in property damage, airbag deployment, or injury were associated with sleepy drivers.

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These numbers are much higher than the current government estimate, which shows that only 1-2% of accidents involve driving while drowsy. Unlike distracted driving or driving under the influence of alcohol, measuring drowsiness is nearly impossible, and some drivers may not want to admit to the police that they were tired in the aftermath of an accident.

But studies show that after 17 to 19 hours without sleep, individuals function at the same level of someone who has a blood alcohol concentration of up to 0.05. Jake Nelson, director of traffic safety advocacy and research at AAA explained that “missing just two to three hours of sleep can more than quadruple your risk for a crash, which is the equivalent of driving drunk.”