Drowsy driving, which killed an estimated 11,000 people on U.S. roads from 2000 to 2010, is a cultural challenge made even more difficult by the fact that it’s nearly impossible to prove.

According to safety experts, drowsy driving is just as dangerous as drinking and driving, though culturally many people don’t think twice about getting behind the wheel if they’re not well-rested. And proving drowsiness is difficult, versus other driver safety hazards like drugs and alcohol, for which there are tests, or even texting while driving, which can also be proven.

Drowsy driving isn’t just a nighttime problem, though most drowsy driving accidents do happen late at night. Drowsy drivers are also a significant concern during daylight hours.

Many national groups dedicated to health and safety—including the U.S. Centers for Disease Control and Prevention, the National Transportation Safety Board, and the National Highway Transportation Safety Administration—hope raising awareness about the problem will make a difference.

To date, only one state has attempted to address drowsy driving with legislation: New Jersey, which passed a law in 2003.

If you feel drowsy behind the wheel, the best thing you can do is get out of the driver’s seat—or get off the road.