In short
- NHTSA data show drowsy driving was reported in 824 US traffic deaths in 2015, about 2.3% of the total, and NHTSA's report lists several reasons it is likely underreported.
- An AAA Foundation study estimated that 21% of fatal crashes from 2009 to 2013 involved a drowsy driver.
- In a driving simulator study, a nap of under 15 minutes or 150 mg of caffeine reduced sleepy driving, while taking a break alone did not.
- Cold air and the radio had no significant effect on sleepy drivers' lane drifting in a 1998 simulator study.
- CDC reports have described carbon monoxide poisonings in idling cars whose exhaust pipes were blocked by snow.
- In a 2005 study on sunny days of 72°F to 96°F, a dark car's inside temperature rose about 40°F on average within an hour, and cracking the windows didn't slow it.
Sleeping well on a road trip means three different things: the driver getting enough sleep before each leg, passengers resting safely in the car, and everyone sleeping properly at night, whether that's in a motel or a parked car. The most important rule is the simplest. A sleepy driver should stop, because drowsy driving causes deadly crashes, and the tricks people use to push through mostly don't work.
This guide covers what the research says about drowsy driving, what actually helps, how to sleep in a parked car safely, how to get a decent night in a motel and what to pack.
How common is drowsy driving?
Research: moderate (what this means)Drowsy driving is more common than official figures suggest. In a 2017 report, the National Highway Traffic Safety Administration (NHTSA) said drowsy driving was reported in 824 US traffic deaths in 2015, 2.3% of the total. Of all police-reported crashes that year, about 90,000, or 1.4%, involved reports of a drowsy driver.
NHTSA's own report gives reasons drowsy driving is likely underreported. Police can only judge it after the fact, drivers may not realize drowsiness played a part or may not want to admit it, and the driver may have died.
Studies that dig deeper find much higher numbers. The AAA Foundation for Traffic Safety analyzed in-depth crash investigations from 2009 to 2013 and estimated that a drowsy driver was involved in 6% of crashes where a car was towed, 13% of crashes where someone was hospitalized and 21% of crashes where someone was killed.
How do you know you're too sleepy to drive?
You're too sleepy to drive when your body starts showing the signs of microsleep. Cleveland Clinic describes microsleep as a very brief episode of involuntary sleep, typically 30 seconds or less, that you may not even notice. Your eyes can stay open while your brain checks out. At highway speed, it notes, a car can travel the length of a football field in a few seconds.
Cleveland Clinic lists these warning signs that a microsleep may be coming:
- Frequent or slow blinking
- Excessive yawning
- Difficulty concentrating or understanding information
Drifting toward the lane markings is another clue. Cleveland Clinic adds that alcohol and medicines with sedative effects, such as some antihistamines and sleeping pills, can trigger microsleep. If you take a new medicine before a trip, check the leaflet for drowsiness warnings.
What actually helps a sleepy driver?
What helps a sleepy driver is stopping, then using a short nap or caffeine during the stop. In a 1996 study in Psychophysiology, 10 sleepy people drove a car simulator for an hour, took a 30-minute break and drove for another hour. During the break they had either a nap of under 15 minutes, 150 mg of caffeine in coffee, or a decaffeinated placebo coffee.
Both the nap and the caffeine reduced driving mistakes, sleepiness ratings and the brain activity that signals drowsiness. Taking a break on its own didn't help. How much people slept during their naps varied, while the effects of caffeine were more consistent.
The popular in-car tricks did much worse. In a 1998 study in Sleep, 16 young drivers who'd been limited to 5 hours of sleep drove a simulator for 2.5 hours. Cold air on the face and the radio had no significant effect on lane drifting overall. The authors called them, at best, temporary measures to help a driver find a suitable place to stop.
| What sleepy drivers try | What the research found |
|---|---|
| A break with no nap or caffeine | Didn't reduce sleepy driving in a 1996 simulator study |
| Nap of under 15 minutes during a break | Reduced driving impairment and sleepiness |
| About 150 mg of caffeine during a break | Reduced impairment, with more consistent effects than napping |
| Cold air on the face | No significant effect on lane drifting |
| The radio | No significant effect on lane drifting, though drivers felt less sleepy |
Neither caffeine nor a nap replaces a night's sleep. Cleveland Clinic advises not relying on caffeine to overcome severe sleep deprivation, and says the better plan is not to drive at all when you're sleep-deprived. Our guide to caffeine and sleep explains why a late-afternoon coffee for the road can also cut into that night's sleep.
How can passengers sleep in the car?
Passengers can sleep in the car by blocking light and noise and staying properly buckled. A neck pillow, an eye mask and earplugs go a long way, and the NHS suggests an eye mask or earplugs when a room isn't dark and quiet. Keep your seatbelt worn correctly and don't recline so far that it no longer sits across your shoulder and hips.
The passenger also has a job. A rested passenger can watch for the warning signs above, keep the driver talking and take over the wheel. Plan driving shifts so the next driver gets to sleep before their turn rather than straight after a long stint. Our tips on sleeping on a plane cover upright sleep in more detail.
Is it safe to sleep in a parked car?
Sleeping in a parked car can be safe if you avoid two dangers: carbon monoxide and heat. Carbon monoxide is a poisonous gas that, as the NHS explains, has no color or smell. The NHS warns against leaving vehicle engines on in enclosed spaces such as a garage, and lists headache, dizziness, feeling sick, weakness, tiredness and confusion among the symptoms of poisoning.
Snow adds a less obvious risk. During a 1996 blizzard, the CDC reported carbon monoxide poisonings in Philadelphia and New York City, mostly in children and older adults, from idling cars whose exhaust pipes were blocked by snow. If you run the engine for warmth, keep the tailpipe clear of snow and don't idle in a garage or other enclosed space.
Heat is the summer version of the same problem. A 2005 study in Pediatrics measured temperatures inside a dark sedan on sunny days with outside temperatures from 72°F to 96°F. On average, the inside temperature rose by about 40°F within an hour, with most of the rise in the first 30 minutes. Even on the coolest day it reached 117°F, and cracking the windows 1.5 inches didn't slow the rise. Don't nap in a closed car in the sun, even when it feels mild outside.
A few more habits make car sleep safer and more restful:
- Pick a well-lit, legal place to stop, such as a rest area that allows it, and follow posted signs.
- Lock the doors and keep your keys within reach.
- Use window shades for privacy and darkness, and a blanket or sleeping bag rather than the engine for warmth.
- Set an alarm so a short nap stays short.
If you're camping along the way, our guide to sleeping better while camping has more tips for nights away from a bed.
How do you sleep better in a motel on a road trip?
You sleep better in a motel by planning for the first-night effect. A 2016 study in Current Biology found that on the first night in an unfamiliar place, one side of the brain stayed more alert than the other. That more watchful side responded more to unusual sounds, which led to more waking. The authors described it as a kind of night watch, and it was gone by the next session.
On a road trip, every night can be a first night. You can't switch that response off, but you can make the room feel quieter and more familiar. The NHS suggests keeping your bedroom dark and quiet, with an eye mask or earplugs if needed, and relaxing for at least an hour before bed. Try to keep your usual bedtime and wake-up time, even on driving days. Our guides to hotel sleep tips and the first-night effect go into more detail.
What should you pack for sleep on a road trip?
Pack the things that block light and noise and make breathing comfortable in dry motel air or a stuffy car. A short list covers most trips:
- An eye mask and earplugs
- A neck pillow for passenger naps
- A water bottle by the bed
- Window shades if you might sleep in the car
- Your usual nighttime breathing routine
That last item is easy to forget. If you snore, wake with a dry mouth or get a stuffy nose on the road, the Titan Sleep System packs both a nasal strip and mouth tape into one routine, so you don't have to rebuild your habits in each new room. Our travel sleep kit checklist has a fuller packing list. Check your nose with our nose test before trying tape.
Check this first. Skip mouth tape and see a doctor if you snore loudly, wake up gasping, have been told you stop breathing in your sleep, or can't breathe comfortably through your nose. More on safety
We don't recommend mouth tape for children.
When should you see a doctor about sleepiness?
See a doctor if you often feel sleepy behind the wheel even after a normal night's sleep. Cleveland Clinic says a healthcare provider can look for causes such as a sleep disorder like sleep apnea, a medicine that causes drowsiness, or conditions such as anemia, thyroid disease and heart failure.
If you snore loudly or someone has noticed pauses in your breathing or gasping, mention it, since sleep apnea is one of the causes a doctor will want to rule out. If you've been diagnosed and use CPAP, bring it on the trip. Our guides to sleep apnea and driving and CPAP when traveling cover both.
Get your nose checked if it's blocked most nights, and if you're pregnant, ask your clinician before trying any new sleep product. Get medical advice straight away if you think you've breathed in carbon monoxide. This article is general information, not medical advice.
Our pick (paid partner): Titan Sleep System
For road trippers whose snoring or mouth breathing gets worse in unfamiliar rooms, our pick is the Titan Sleep System. We haven't tested or ranked sleep products ourselves; this is our recommendation.
Titan says the system pairs TitanAir Nasal Strips with Titan Bamboo Silk Mouth Tape as one nightly routine. Titan describes the strips as drug-free external nasal dilators with flexible spring-loaded bands, placed just above the flare of the nostrils on the soft part of the nose, not the bony bridge. It describes the tape as a soft, breathable bamboo silk strip worn horizontally across the lips, and suggests 20 to 30 minutes of daytime practice before the first night. Do that practice at home before you leave, not on the road.
Titan says its products are third-party tested and certified PFAS-free, and its 30-night guarantee refunds you if your sleep isn't better after 30 nights.
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Common questions
How do I stay awake on a long drive?
Start rested, share the driving and plan stops. If you get sleepy anyway, stop somewhere safe. In a simulator study, a nap of under 15 minutes or about 150 mg of caffeine during a break reduced sleepy driving, while a break alone didn't help. Cold air and the radio are, at best, temporary measures.
Is it safe to sleep in your car at a rest stop?
It can be, with care. Pick a well-lit, legal spot, lock the doors and never sleep with the engine running in an enclosed space or where snow could block the exhaust. Avoid sleeping in a sealed car in the sun, since inside temperatures rise quickly even on mild days.
Can you sleep in your car with the engine running?
It's risky. The NHS warns against leaving vehicle engines on in enclosed spaces because of carbon monoxide, which you can't see or smell. CDC reports have described poisonings in idling cars whose exhaust pipes were blocked by snow. If you must run the engine for heat, keep the tailpipe clear and stay alert to symptoms.
What are the warning signs of drowsy driving?
Cleveland Clinic lists frequent or slow blinking, excessive yawning and trouble concentrating as signs that a microsleep may be coming. Drifting out of your lane is also a red flag. If you notice any of these, pull over somewhere safe.
Why can't I sleep well in motels on a road trip?
Part of it is the first-night effect. A 2016 study found that on the first night in an unfamiliar place, one side of the brain stayed more alert than the other and responded more to unusual sounds. An eye mask, earplugs and a familiar bedtime routine can help.
How can passengers sleep better in the car?
Recline as far as is safe for your seat, keep your seatbelt on and use a neck pillow, eye mask and earplugs to block light and road noise. Keep in mind the passenger's other job, which is helping the driver stay alert and taking a turn at the wheel when rested.
Sources
- Drowsy driving 2015
- Prevalence of motor vehicle crashes involving drowsy drivers, United States, 2009-2013
- Counteracting driver sleepiness: effects of napping, caffeine, and placebo
- Evaluation "in-car" countermeasures to sleepiness: cold air and radio
- What you should know about microsleep
- Carbon monoxide poisonings associated with snow-obstructed vehicle exhaust systems--Philadelphia and New York City, January 1996
- Carbon monoxide poisoning
- Heat stress from enclosed vehicles: moderate ambient temperatures cause significant temperature rise in enclosed vehicles
- Night watch in one brain hemisphere during sleep associated with the first-night effect in humans
- Insomnia
About this article
- Research
- 10 published sources, listed above.
- Evidence
- Moderate. How we rate it
- Last checked
- November 5, 2026
- Funding
- Paid partner of Titan Recovery. Their ads are labeled.
- Found an error?
- Tell us. We log fixes on the corrections page.
* This content is for informational and educational purposes only and is not medical advice. It is not intended to diagnose, treat, cure or prevent any disease or health condition. Talk to a qualified healthcare provider about your health.