By Lynne Adkins

PHILADELPHIA (CBS Philly) — Sleepy driving is a huge problem, but it’s one that most of us don’t recognize.

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Drowsy drivers may cause nearly a third of all deadly car crashes according to federal statistics and a study at the University of Pennsylvania Health System proves the danger.

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“A lot of people don’t realize that more serious crashes are caused by falling asleep at the wheel than alcohol,” Dr. Michael Grandner said. “Though we’ve all heard of drunk driving, we haven’t heard much about drowsy driving, but it’s a major health problem and safety problem.”

Dr. Grandner, a member of the Center for Sleep and Circadian Neurobiology, says a survey of more than 17,000 people showed that most people need at least seven hours of sleep each night. He says, “People who reported five hours or less per night were 3-4 times as likely to report dozing off at the wheel in the last month as compared to people who say they slept an average of seven hours a night.”

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Dr. Grandner says it didn’t matter if the person felt he or she had gotten enough sleep, too little shuteye still affects time behind the wheel.