A wake up call for drowsy drivers

Dear Alice,

What causes people to fall asleep in cars even when they are driving and not sleepy?

Dear Reader,

Drowsy driving is when someone gets behind the wheel while feeling sleepy or otherwise fatigued. Some people may be in situations that affect how alert they are at the wheel, and they may not even realize it. Lack of sleep affects driving in ways similar to alcohol: both can lead to slower reaction times; impaired coordination, judgment, and vigilance; and increased aggressiveness. In addition to lack of sleep, a variety of health conditions could contribute to a person falling asleep at the wheel. Most of these drowsy driving situations happen between midnight and six o'clock in the morning, but they can happen at any time of day. 

Sleep deprivation can be a risk factor for falling asleep while driving. According to the National Safety Council, driving without sleeping for over 20 hours is similar to being too drunk to drive, at which a person would be at the U.S. blood-alcohol concentration legal limit of 0.08 percent. Drowsy drivers are three times more likely to end up in a car accident and contribute to up to 6,000 car crashes every year. Here are some warning signs that you might be too sleepy to drive:

  • Inability to focus or keep your eyes open and head raised
  • Repeated yawning or frequent blinking
  • Difficulty remembering the last few miles you traveled
  • Hitting the shoulder rumble strip, tailgating, or drifting out of your lane
  • Missing planned exits or ignoring traffic signs altogether
  • Inability to maintain a consistent speed

Another reason that people may fall asleep while driving is due to a variety of health concerns. Some medications have a sedative effect that affects people's ability to operate machinery such as a vehicle. These can include antihistamines, antidepressants, or prescription painkillers, among other medications. For those who are concerned, you can check the warnings of any drugs (prescription or over-the-counter) to see if there are any messages about driving or operating heavy machinery or speak with a health care provider. Untreated sleep disorders, such as sleep apnea or narcolepsy, could also be the culprit.

Young drivers are also more likely to be in drowsy driving crashes; about half of these crashes are from drivers under 25 years old. This may be because they are more likely to drive late at night, or have so many work, school, or social commitments that sleep time suffers. If you tend to get sleepy when you ride in cars, it's important to be extra aware of these risk factors so that you can be sure you're safe to drive. For more info on sleep and sleep problems, you can check out the Sleep section of the Go Ask Alice! General Health archive.

Despite popular misconceptions, driving with the radio pounding at your eardrums, stopping to exercise, and opening the windows to let a blast of wind blow you awake have NOT been shown to increase driver attentiveness. Caffeine can make you more alert, but it takes about 30 minutes to kick in and wears off after a few hours. Excess amounts of caffeine can also contribute to sleep problems. To best avoid drowsy driving, it helps to plan ahead. This might mean:

  • Carefully reading medication bottles, then avoiding medications and alcohol that can have sedative effects
  • Establishing boundaries at work to avoid long, fatiguing shifts
  • If you have the financial means, investing in crash avoidance technology for your car
  • Getting a full night's sleep, about seven to eight hours a night
  • Speaking with a provider about a sleep disorder diagnosis and possible treatment options

But if you're already on the road, it may help to look for a safe place to pull over and take a short nap (with the doors locked), but more than 20 or 30 minutes sleep can leave you feeling drowsier than before. Better yet, if you’re able, consider finding a place to get a full night’s rest. In short, the best bet is to make sure you snooze before you cruise.

Wishing you sweet drifting in sleep and safe drifting on the roads,

Last updated Jan 20, 2023
Originally published Apr 26, 2002

Submit a new comment


This question is for testing whether or not you are a human visitor and to prevent automated spam submissions.

The answer you entered for the CAPTCHA was not correct.