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Dangers of Drowsy Driving

Missing one hour of sleep may duplicate car crash risk

Think you can get by during a busy week with just a few hours of sleep and copious amounts of coffee? A study by American Automobile Association Foundation for Traffic Safety sheds light on how dangerous sleep deprivation can be.

Missing just an hour or two of sleep at night nearly doubles your chances of a car crash the following day, the study states. More worrying is that driving after only four to five hours of shut-eye quadruples that risk. This risk is comparable to driving with a blood-alcohol concentration that is considered to be legally drunk in most US states, according to the research.

“This is the first study to actually quantify the relationship between lack of sleep and the risk of being involved in a motor vehicle crash,” according to report author Brian Tefft, who adds that the risk of sleep-impaired driving has long been “underestimated and underappreciated”.

Bryan Thomas, from the US National Highway Traffic Safety Administration, adds: “Not everyone drinks and drives or texts while driving but everyone gets tired. And far too often, drivers are putting themselves and others at risk by getting behind the wheel without the sleep they need.”

Ideal amount of sleep

National sleep organizations recommend that healthy adults need between seven and nine hours of sleep each night. Teens, young adults and people recovering from a sleep deficit may need even more slumber, according to the report.

The research

The survey consisted of a representative sample of nearly 4600 police-reported crashes from July 2005 to December 2007. These crashes involved at least one vehicle towed from the scene and the dispatch of emergency medical personnel.

Drivers who contributed to crashes were more likely to report having slept less than usual in the previous 24 hours. They were also more likely to have altered their sleep schedule in the past seven days. The youngest and oldest drivers were the most culpable in these drowsy driving-related accidents. By contrast, drivers who did not contribute to crashes were mostly middle-aged, the report says.

Sleep apnea

Lack of sleep may also be caused by physiologic sleep disorder, when your breathing stops and starts while you sleep (sleep apnea). There may be a physical blockage in the throat, which may be a reason of snoring. Central sleep apnea occurs when the brain does not send signals to the muscles that control breathing. 

In Hungary, an examination for sleep-disordered breathing (OSA) may be required for getting a driving license or for its renewal. If there is a suspicion of sleep apnea, you must meet with a specialist.

Lack of sleep slows reaction times, decreases the accuracy of response and leads to long lapses in attention, which could lead to dangerous situations while driving.

Warning sign? No!

Are there warning signs you’re too drowsy to drive safely? Having trouble keeping your eyes open, drifting from one lane to another, or not remembering the last few kilometers driven are all reasons for concern. Yet, alarmingly, more than half of drivers involved in fatigue-related crashes experienced no symptoms before falling asleep behind the wheel.

Dr. Erich Voigt, chief of the division of general/sleep otolaryngology at New York University Langone, advises that drivers should not rely on their bodies to provide warning signs that they are too tired to drive.

“It’s a matter of being honest with yourself and perhaps having someone else drive, or if you’re traveling with someone, have them look for the signs of you being too sleepy,” he said on national television. “Or take a cab or public transport. Or don’t take the trip at all.”


For longer road trips, the American Automobile Association gives general recommendation for drivers:

  • Travel at times when you would normally be awake.
  • Schedule a break every two hours or every 150 kilometers.
  • Avoid heavy foods.
  • Travel with an alert passenger and take turns driving.
  • Avoid medications that can cause drowsiness or other impairment.

None of this should come as a surprise to any driver. We’ve all been in that situation. You’re on a long trip, been driving for hours straight, then all of a sudden you jerk your head up realizing you were about to doze off. If you’re smart you pull off, maybe take a short nap or at least get some air. If you’re not so smart you try to push it, potentially setting yourself up for a lot of rest in a hospital bed. Follow the tips above and stay alert.

Safe travels, everyone.

Schedule a visit with our sleep specialist if you need professional help to improve your sleep.


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