One Hour of Sleep: A Matter of Life and Death

gray highway with cars in the distance

The AAA Foundation for Traffic Safety recently conducted the first-ever study to actually quantify the relationship between lack of sleep and car crash risk. A comprehensive examination showed that shorting yourself just one hour of sleep can double your crash risk the next day. And operating a motor vehicle on only 4 to 5 hours of sleep quadruples your crash risk, impairing your faculties to the same degree as driving with a blood alcohol level in the legally drunk range.

One More Reason to Prioritize Sleep

The National Sleep Foundation recommends that adults get 7 or more hours of sleep a night, with teens, young adults, and those recovering from lack of sleep clocking in additional hours of shut-eye. Getting behind the wheel with less than 7 hours of sleep has been shown to impair reaction times, response accuracy, and concentration.

“[B]efore this study, we did not have real-world evidence of the size of the increase in crash risk in relation to the degree of acute sleep deprivation,”

The AAA Foundation for Traffic Safety analyzed data from a NHTSA survey of approximately 4,600 police-reported crashes from July 2005 to December 2007 that required the dispatch of emergency medical personnel and the towing of at least one car. Each crash was evaluated by uniquely trained investigators who examined contributing factors to the crash, including the drivers’ regular sleep schedules, changes to those schedules, and how much sleep they got 24 hours prior to the crash. They estimated crash risk by measuring the actual amount of sleep against the suggested 7 or more hours. Researchers also pitted the amount of sleep drivers responsible for the crashes got against the amount of sleep drivers not responsible for the crashes got.

restless man holding his face in his hand

Results indicate that crash risk increases successively for each hour of sleep you miss. Drivers operating a motor vehicle after getting just 4-5 hours of sleep are 11.5 times more likely to crash than are drivers who’ve gotten 7 or more hours of sleep. The effect of 4-5 hours of sleep matches that of driving with a blood alcohol level of 0.12-0.15 (the level for legally drunk starts at 0.08).

The report uncovered a few more notable results. In general, drivers at least partly responsible for crashes slept less than normal in the 24 hours prior, and were also much more likely to have shifted their sleep schedules within the previous 7 days. According to crash records, the youngest and oldest drivers were the most affected by sleep deprivation. 

How to Know When You’re Too Sleepy

You might not feel the effects of 1 fewer hour of sleep a night, but you can remain vigilant when it comes to driving while drowsy. The National Sleep Foundation highlights the following signs that you are too tired to drive and should stop and rest:

  • Focusing becomes difficult
  • You start to blink a lot
  • Your eyelids feel heavy
  • Your thoughts start to wander and seem more random than usual
  • You go from one point to another without remembering how you got there
  • You miss your exit or blow through traffic signs unaware
  • You yawn frequently
  • You keep rubbing your eyes
  • You have difficulty keeping your head up
  • You start to drift from your lane or tailgate
  • You feel grumpy and restless
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