New research shows that being sleepy behind the wheel may cause more accidents than previously thought—especially at night.

In a startling wake-up call, a new study from AAA reveals that up to 9.5 percent of all motor vehicle crashes involve drowsy driving. That’s far higher than previous government estimates of between 1 and 2 percent, a finding that has serious implications for anyone on the road. By comparison, the National Highway Traffic Safety Administration estimates show that 5 percent of all crashes involve alcohol-impaired drivers.

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“Most people think their driving will only be impaired if they’ve had something to drink or taken any drugs, whether prescription or recreational. They don’t consider being fatigued as a real risk factor, when in fact it is a severe impairment,” said Emily Thomas, Ph.D., automotive safety engineer at Consumer Reports. “Your ability to focus, your reflexes, state of awareness are all impacted by tiredness and increase the risk to yourself and those on the road around you.”

To address the disparity between the AAA study and existing data, we reached out to a NHTSA spokesman, who let us know that driving drowsy “is likely to be under-reported as a cause of crashes because of the challenges in establishing whether a crash-involved driver was drowsy.”

Prior research relied on reports from law enforcement who asked drivers whether they were drowsy in the moments after a crash. AAA’s study looked at dash-cam footage of real crashes to determine whether the driver was exhibiting signs of drowsiness.

AAA’s researchers worked with the Federal Highway Administration’s second Strategic Highway Research Program (SHRP2) to examine dash-cam footage from 3,593 drivers, measuring the percentage of time that a person’s eyes were closed in the final moments ahead of 589 crashes. (Drivers whose eyes were at least 80 percent closed for 12 percent or more of video frames in the 1 to 3 minutes prior to the crash were considered to be exhibiting signs of drowsiness.)

In addition to the main findings, results indicated that more than half of all drowsiness-related crashes took place after dark. Drowsiness was a factor in 10.8 percent of crashes severe enough to be reported to the police, and the age or gender of the driver had no effect on the percentage of drowsy-driving crashes.

New advanced safety technology, designed to take control of a vehicle when the driver fails to react to a hazard, may address some of the dangers of drowsy driving.

“It is just these type of scenarios where advanced safety features like forward-collision warning (FCW), automatic emergency braking (AEB), and lane-departure warning (LDW) can have lifesaving benefits for bringing a fatigued driver to attention,” says Jennifer Stockburger, CR’s Auto Test Center director of operations.

Still, the best way to avoid a drowsy driving-related crash is to get enough sleep—and to pull over before you’re having trouble staying awake.

Tips to Prevent Drowsy-Driving Crashes

  • Don’t get behind the wheel if you’re tired.
  • If you find yourself at the wheel struggling to stay awake, change drivers. 
  • If you’re alone, pull over somewhere safe and take a short power nap.
  • Try some caffeine, although it takes about 30 minutes to feel the effects.
  • Travel during daylight times and not overnight.
  • Take a break every 2 hours or 100 miles.
  • Consult a sleep specialist if you have trouble sleeping or are always tired.