Q: I was reading about how a lack of sleep affects our brain, and it got me wondering how it affects our driving. What kind of data are there around drowsy driving?
A: As I write this it’s the Monday after setting the clocks forward an hour. I feel like I started my day a half-hour ahead of schedule, but I’m actually behind. I could go on a tangent about the loss of productivity and actual physical harms caused by daylight savings, but since you’ve been reading about the problems associated with a lack of sleep you probably already know that.
Falling asleep while driving is obviously a problem. I don’t think that needs any explanation. Even if you’re at the point of rolling down the window and turning up the stereo to prevent nodding off, we have a safety issue. If you’ve convinced yourself that closing one eye at a time while you drive is a reasonable solution to your exhaustion, well, it’s not; you’re not a dolphin. But you are sleep deprived. (Nature trivia – dolphins can sleep with one eye open. They rest half their brain at a time so they can watch out for predators and come up for air.)
But what about if you were just short an hour or two of sleep last night? Or maybe a few nights in a row? Even if you don’t feel like you need a nap, sleep debt (when you owe yourself more sleep than you got) is bad for driving. It doesn’t take a lot of sleep deficit to create cognitive impairment. Daylight savings is proof of that. Traffic crashes, workplace injuries and heart attacks increase in the days after we spring forward.
Sleep debt affects your reaction time, judgment, vision, awareness, and decision-making skills. If you’ve read much about alcohol impairment that list probably sounds familiar. Lack of sleep impacts your ability to drive similar to drinking alcohol. Though not identical, there are concerning parallels. After being awake for 18 hours, drivers perform similar to a person with a .05 blood alcohol concentration. At 20 hours, performance drops to that of a driver with a BAC of .08. That translates to a crash risk of 11 times that of a sober or alert driver. Just being an hour or two short on sleep doubles your risk of a crash. Being three or more hours short doubles it again.
Drowsy driving is a factor in about 100,000 police-reported crashes each year in the US, resulting in over 1500 fatalities. However, drowsiness is underreported in fatal crashes. Collision investigators can figure out if a vehicle was speeding based on crash evidence, and can determine impairment from blood tests, but if a driver doesn’t admit to being drowsy, or is the victim of the crash, it’s hard to confirm drowsiness as a factor. The actual number of fatal crashes involving a drowsy driver is likely around 6000 each year.
In addition to lack of sleep, some medicines cause drowsiness. The tree in my back yard sprouted buds, which means allergy season is nearly upon us, and allergy medications are one of the most common drugs that can make you feel tired. When a drug is solving one problem it’s easy to forget that it might cause another, like messing with your driving.
We all can be impaired by a lack of sleep but, like many driving risk factors, young drivers are over-represented. Fifty-five percent of drowsy driving crashes involve someone under 25 years old. If that’s you, I give you permission to go to bed early or take a nap.
Years ago a young coworker stated that he sleeps six hours a night instead of eight because he didn’t want to “waste” one third of his life. Ironically, those few years of consciousness potentially gained may not make up for poor quality of life resulting from falling asleep at the wheel and maiming yourself (or worse).