Russell Hebets Dec. 12, 2016

AAA recently released a study indicating that crash risk increases for every hour of sleep lost. While it has long been understood that sleepiness affected driving negatively, this study looked more closely at the situation in order to define what that means for drivers.

How Much Sleep Does One Need?

The National Sleep Foundation and other experts recommend that adults get 7-9 hours of sleep per night, and some people may require more, especially if they are ill or recovering from an illness, injury or a sleep debt.

According to the CDC, 35% of the population sleeps for 7 hours or less and 12% sleep less than 5 hours in a given 24-hour period. Sleep deprivation slows down reaction time and decreases accuracy; it can also lead to long lapses in attention, in other words, spacing out.

Sleep Deprivation and Driving

Previous to this study there has not been a comprehensive look at how sleep affects driving. However, it was believed that 13% of crashes and as many as 21% of fatal accidents involved a drowsy driver.

The AAA decided these estimates were not enough and embarked on a two and a half year survey of crash information. The study looked at crashes from July of 2005 through December of 2007 during the hours of 6 am to midnight and surveyed reports and drivers about a variety of things including how much sleep they got and changes to their sleep schedules around the time of the crash. The survey was designed to rule out other factors and was conducted by independent investigators and not law enforcement.

The study found that there is a significant increase in crash risk for anyone who got less than 7 hours of sleep and the risk increased with each hour of sleep lost. At 6-7 hours of sleep, drivers had 1.3 times the crash rate, at 5-6 hours of sleep they had 1.9 times the crash rate, at 4-5 hours, they had 4.3 times the crash rate, and at less than 4 hours, they had 11.5 times the crash rate of well rested drivers.  

Drivers who regularly average 4-5 hours of sleep rather than 7 hours of sleep increase their overall risk by 5.4, indicating a cumulative negative effect of sleep deprivation on safe driving.

Clearly sleep deprivation and good driving are strongly connected. In fact, the National Sleep Foundation says someone who has slept 2 hours or less in a 24 hour period absolutely should not drive.

How Does this Compare with Drunk Driving?

The crash risk of a driver who only slept for 4-5 hours is comparable to someone driving with a blood alcohol level of.08 the national legal limit for DUI. For someone who slept less than four hours, their crash risk is like a drunk driver with a BAC of .12 to .15.  

This begs the question:  Should drowsy driving be criminalized? Also, is Texting While Driving worse than DUI?