(AP) — Many Americans admit they’ve done it, but safety experts say drowsy driving is a problem motorists are just starting to wake up to.

A fatigue expert on the National Transportation Safety Board says drowsy driving can be as bad as drunken driving.

Police today can easily determine how much alcohol is in a driver’s blood or whether someone has taken illegal drugs. But proving a driver’s drowsiness is not as easy.

A bus driver was recently acquitted of manslaughter and negligent homicide in a 2011 New York City bus crash that killed 15. Prosecutors alleged he was all but asleep at the wheel, but a jury decided there wasn’t enough proof to convict him.

Federal statistics show more than 11,000 deaths were attributed to drowsy driving from 2000 to 2010.