It’s been well-known for a long time that there are many factors that can increase your car wreck risk and that one of them is lack of sleep, but a new study has pinpointed exactly how much shuteye you can’t afford to be without. Falling asleep behind the wheel could put you at risk of being seriously injured in an accident, or worse, hurting someone else.

Across the U.S., one in every five vehicle crashes is tied to someone being drowsy behind the wheel. Much like how distracted driving can amplify car wreck risk, drowsy driving is a behavior that can be prevented. If you don’t pay attention to that drowsy feeling behind the wheel, you may end up causing a severe accident.

According to AAA, even missing one or two hours of sleep can up your car wreck risk. After a recent government study, it was discovered that one-third of people currently driving vehicles on U.S. roads were doing so tired enough to cause deadly accidents. That’s because 35 percent of people all over the nation aren’t getting enough sleep to function effectively on a daily basis, according to the CDC. The Automobile Club of Southern California has shared that getting less than five hours of sleep each day quadruples a person’s car wreck risk.

Aside from putting yourself, your vehicle, and your passengers at risk of a major car crash, the consequences for an accident may be more severe if you hurt or kill someone else in the process. If you are taking a long trip, when it’s easy to get distracted or drowsy behind the wheel, plan in stops every two hours or so even if they are just to stretch your legs outside of the car. Try to avoid driving during the time of day when your body has been programmed to get ready for bed and fall asleep, as this could increase your chances of drifting off and causing a vehicle crash.