Safety experts often talk about the “three D's of dangerous driving” — drinking, drugs and distraction. But there’s a fourth “D,” according to Jonathan Adkins, executive director of the Governors Highway Safety Association.

"Drowsy driving came on the radar about ten years ago,'' he says. And while operating a vehicle while tired or sleep-deprived is dangerous for all drivers (and their passengers, and everyone else on the road), teenagers may be especially likely to climb behind the wheel while too fatigued to maneuver a car safely.

"Teens are not the safest drivers under optimal conditions," Adkins says. According to the Centers for Disease Control and Prevention (CDC), driving while drowsy is one of eight ''danger zones'' for teens. (The others include inexperience, distracted driving, nighttime driving, not wearing seatbelts and impaired driving.)

And the temptation, or need, to drive while tired may be significant. "Teens have so much pressure on them, not only with school but with the after school activities," Adkins says. "It's a competitive time in their lives." What's more, FOMO, or fear of missing out, will often compel a kid to drive when he really should be resting. "That fear of missing out is huge for teens," Adkins says.

Related: Why You Should Let Your Teen Driver Drive the New Car

The National Sleep Foundation, which sponsors a national Drowsy Driving Prevention Week each year, reports more than half of all asleep-at-the-wheel crashes involve drivers who are 25 years old or younger.

What parents can do

It may seem easier said than done, given the teenage mindset that as almost-adults they can handle their own lives and schedules, but it’s important for parents to help teenagers avoid driving while drowsy. Adkins suggests these strategies.

Related: How to Help Your Teen Get Enough Sleep

Insist your child is well rested before you’ll hand over the car keys. "You wouldn’t give your teen the keys if he was impaired by medicine or if he was sick," Adkins says. Drowsy driving is just as hazardous. "If your kid has pulled an all-nighter, the last thing you want him to do is get behind the wheel," Adkins says.

Make sure kids know how much sleep they need. Nine hours is optimal on school nights, according to the National Sleep Foundation. Only one in five teens get that much, though, and about half of all teenagers sleep fewer than eight hours on school nights.

Warn them about the “other guy.” Let your teenager know you aren’t just concerned about his driving ability, but you’re also aware of potentially unpredictable behavior by other drivers — another reason to be rested while driving.

Make sure your teen knows how to tell if he’s too wiped out to be driving. According to the National Sleep Foundation, signs include trouble focusing, rubbing your eyes, daydreaming, drifting from lane to lane or missing exit signs.

Explain what to do if your kid gets sleepy while on the road. Tell him to find a safe spot, such as a well-lit rest area, where he can take a nap, Adkins says. Stopping to take a walk in the fresh air also can help.

Put the FOMO thing in perspective. Encourage your child to think beyond missing tonight’s party, advises Adkins. Remind him he needs to be as safe as possible now to reach his long-term goals of going to college and starting a career and living a long, productive life.

Related: The Scary Truth About Teen Drivers, and How You Can Keep Them Safe

Kathleen Doheny is a Los Angeles journalist specializing in health, behavior and fitness topics.