Driving Tired is Probably Worse Than You Thought

Q: I see ads about distracted driving, impaired driving, speeding, and wearing a seat belt, but where are the messages about drowsy driving? It seems to me like falling asleep while driving would be more dangerous than any of those. I’ve seen drivers at night drifting out of their lane, and I don’t see a glow from their phone’s screen, so I’m assuming they’re too tired to drive. How bad is this problem?

A: Let’s start with aliens. The cosmologist Martin Rees said, “Absence of evidence is not evidence of absence.” Or stated another way, just because we haven’t seen any aliens doesn’t mean they don’t exist.

Drowsy driving may not have the same existential impact as the discovery of aliens, but we have a similar problem. After a crash, a collision investigator can take a breath or blood sample to see if a driver was impaired, the extent of damage can be used to determine speed, and injuries can show whether a person was wearing a seat belt.

But there isn’t a test to prove that a driver was too tired to drive. Evidence at the crash site, like a lack of skid marks or effort to course correct, can hint at it but it’s hard to know for sure. Talking with the driver probably won’t help because all the adrenaline released in the crash will perk them up, at least temporarily. There’s an absence of evidence for a very real problem.

Because of that, drowsy driving crashes are likely under-reported. By a lot. The official report for 2023 shows 633 traffic fatalities in the US attributed to drowsy driving. But because of what I just mentioned, along with inconsistent methods of documenting fatigue-involved crashes from state to state, the Governor’s Highway Safety Association calls that a “substantial undercount.” A comprehensive analysis puts the likely number at over 6300. 

Yes, falling asleep while driving is incredibly dangerous. And the problems start before we doze off. Lack of sleep results in reduced attention, slower reaction times, poor judgement, and loss of fine motor skills. You might have noted that those are similar to the effects of alcohol. The parallels continue. Research shows that driving tired (after being awake for 17 to 19 hours) is similar to having a blood alcohol level of .05, the per se limit in many countries and the state of Utah. By 20 hours without sleep the effects are comparable to a .10 blood alcohol level.

How big is the problem? Transportation experts estimate that about 1.5 percent of drivers on the road are drowsy. But driver fatigue is estimated to be a factor in over 17 percent of fatal crashes. The good news is that nearly all of us (97 percent) agree that drowsy is unacceptable and a serious threat to safety. The bad news is that one in three of us admit to doing it, at least occasionally.

This is one of those problems with a simple solution – more sleep. Not rolling down the windows, not turning up the radio, not caffeine (it feels helpful but also masks the problem.) Sometimes, though, simple solutions are hard to implement. In a culture that doesn’t value sleep we’re tempted to over-commit, either out of necessity or because we’ve put unrealistic expectations on ourselves.

If driving risk isn’t enough to convince you, realize that getting enough sleep is important for all of life – your family life, your job performance, your creativity. It’s just that sleeping through those things will be a slow calamity, while sleeping behind the wheel will be a calamity all at once.