A wake up call for drowsy drivers

Originally Published: April 26, 2002 - Last Updated / Reviewed On: December 23, 2008
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Dear Alice,

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

Dear Reader,

You're driving down the interstate late at night (though not always at night), cruise control on, radio playing softly, and the steady thump of the tires on the pavement echoing the beat of your heart. Burr-UMP... Burr-UMP... Burr-UMP. A conditioned response from babyhood may kick in, where one finds the car warm and safe, and the motion soothing. It's enough to send the most chronic insomniac off to dreamland.

According to the National Highway Traffic Safety Administration, drowsy driving is responsible for at least 56,000 collisions and over 1,000 deaths every year. 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. Some warning signs that your drowsiness may be affecting the way you drive are:

  • not being able to focus or keep your eyes open and head raised
  • repeated yawning
  • difficulty remembering the last few miles you traveled
  • daydreaming or having your mind wander
  • hitting the shoulder rumble strip, tailgating, or drifting out of your lane

Risk factors for being in a drowsy driving crash include:

  • Night time driving: Most drowsy driving crashes happen between midnight and 6 A.M.
  • Sleep deprivation: Fatigue caused by sleep problems, working double or late-night shifts, or simply doing too much work with not enough rest
  • Medication that has sedative effects: Some medicines, such as antihistamines, antidepressants, or prescription painkillers, can cause unexpected bouts of sleepiness.
  • Untreated sleep disorders: Sleep disorders, such as sleep apnea and narcolepsy, can lead to sleep-related crashes.

Young drivers are also more likely to be in drowsy driving crashes, perhaps because they are more likely to drive late at night, or have so many work, school, and/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, check out the Sleep section of the General Health archive.)  In addition, at least one state, New Jersey, explicitly defines drowsy driving as reckless under its vehicular homicide laws; several other states have similar legislation pending. Even so, most states' current reckless driving laws can still be used to prosecute drowsy drivers, which may result in fines, loss of driver's license, or even imprisonment.

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 thirty minutes to kick in and wears off after a few hours. Excess amounts of caffeine can also cause sleep problems. 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. In short, the best bet is to make sure you snooze before you cruise.