Drowsy driving could be responsible for thousands more deaths on U.S. roads every year than first thought. New research out from AAA says drowsiness could play a part in nearly 10 percent of all crashes. In the last month, 29 percent of drivers admit to being behind the wheel when they had a hard time keeping their eyes open.

Researchers and police have long suspected drowsy driving was an underreported factor in crashes. Now, the Centers for Disease Control and Prevention recommends adults get least seven hours of sleep a night. Researchers say when people get less than that and drive drowsy, it can be as dangerous as driving drunk, reports CBS News correspondent Kris Van Cleave.

A drowsy driving crash killed Jennifer Pearce's 18-year-old sister, Nicole. The Virginia Tech freshman was coming back from a ski trip with four friends when the driver fell asleep and slammed into a tree.

"For 10 years we've had to deal with her loss and not just the loss of who she was at 18, but the loss of the many years and who she would have become," Pearce said.

AAA researchers studied videos from cameras mounted in cars of 3,500 drivers looking for signs of fatigue. Federal estimates cite drowsiness as a factor in one to two percent of crashes. When researchers analyzed more than 700 crashes caught on tape, they found signs of drowsy driving in roughly 10 percent.

"There's really no truly effective countermeasure to drowsiness as sleep. So it really comes back to trying to plan and give yourself enough time to get that sleep," said William Horrey from the AAA Foundation for Traffic Safety.

If getting seven to nine hours of sleep a night sounds more like a luxury, researchers say keep in mind the risk is greatest at night. Signs to watch out for include having trouble keeping your eyes open, drifting from your lane and not remembering the last few miles you've driven.