The number of crashes involving drowsy drivers could be significantly higher than official statistics suggest, according to a report published by the AAA Foundation for Traffic Safety.

“Prevalence of Drowsy Driving Crashes: Estimates from a Large-Scale Naturalistic Driving Study” identifies drowsiness as a factor in 8.8%-9.5% of all crashes examined. The official U.S. government estimate is 1%-2%.

“Drowsy driving is a bigger traffic safety issue than federal estimates show,” said Dr. David Yang, Executive Director for the AAA Foundation for Traffic Safety. “Drivers who don’t get enough sleep are putting everyone on the road at risk. By conducting an in-depth analysis using video of everyday drivers, we can now better assess if a driver was fatigued in the moments leading up to a crash.”

For the study, more than 3,500 people were monitored continuously for several months using in-vehicle cameras and other data collection equipment. Drowsiness was assessed using a validated measure based on the percentage of time that a person’s eyes are closed.