Driving under the influence…of fatigue

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Going on a long car trip this summer? Planning to make good time? Going to drive all night, maybe?

Well, don’t.

Statistics are somewhat unreliable, because there’s no good way to test for it, but it’s estimated that about 16 percent of all vehicle accidents are caused by driver fatigue. That’s 35,000 accidents a year in Canada.

Back in 2000, Alistair MacLean, head of the psychology department at Queen’s University, published a study that found that sleep-deprived drivers were just as impaired as drunk drivers.

MacLean studied the driving performance of men and women with good sleep habits. He asked them to drive at various hours of the night. He found that at 2:30 a.m., they drove with the same level of competence as drivers with a blood alcohol level of 0.05 percent—the level of impairment normally achieved by a 160-pound man who drank three gin-and-tonics in an hour.

By 5 a.m., the men and women’s performance had sunk to the level of someone with a blood alcohol level of 0.08 percent—making them legally impaired, if there were a breathalyzer test for fatigue, which unfortunately there isn’t.

Fatigue-related accidents occur most frequently within two distinct time periods: between midnight and 6 a.m., and between 2 p.m. and 4 p.m. That’s not accidental: it’s the way our bodies are wired.

Like most organisms, we have built-in clocks that govern our “circadian rhythm,” our pattern of alertness. (“Circadian” comes from the Latin words circa, meaning about, and dies, meaning day.) Human circadian rhythms are controlled by a region of the brain called the suprachiasmatic nucleus, or SCN, which is located in the hypothalamus, a region of the brain that regulates many of the tasks of the autonomic nervous system.

One way the SCN controls the circadian rhythm is by stimulating the production of a hormone called melatonin, which is manufactured by the pineal gland, located at the base of the brain. Typically, melatonin levels increase after sunset, peaking between midnight and 6 a.m.—the time when both our level of alertness and our body temperature is at its lowest. There’s a second dip in the afternoon, typically between 2 and 4 p.m., a.k.a. nap time. And thus, that’s when driver fatigue is most likely to be a factor in accidents.

Fatigue works its dark magic (sorry, I’ve just been reading Harry Potter) in four ways.

First, it slows reaction time, which means that if, say, a car abruptly emerges from a side street, a fatigued driver is less likely to be able to avoid hitting it, either by braking or steering around it.

Second, it reduces vigilance. Sleep-deprived people just have a harder time paying attention to what’s going on around them. In driving terms, that means a sleepy driver is less likely to notice possible hazards, like road work, a railway crossing, or deer in a ditch.

Third, fatigue makes it harder for people to process information, and also affects their short-term memory. A sleepy driver is slower to realize that something up the road calls for a reduction in speed, for instance. He may “zone out,” suddenly realizing that he can’t even remember the last few minutes of driving.

But the killing curse of fatigue (to extend my Potterish metaphor) is sleep itself. Seated comfortably in a temperature-controlled environment with very little sensory input, especially late at night, it’s not surprising that people drop off into those micro-naps that, in a comfy chair, usually end with you jerking upright from a brief dream of falling, but that in a car can end with you in the wrong lane facing an onrushing semi, or rolling over in the ditch.

So, what can you do to prevent becoming a driver-fatigue statistic?

Well, the obvious thing is to get enough sleep. Other than that, you need to set realistic travel goals (don’t plan for 14-hour days), schedule in plenty of rest stops, recognize when you’re getting sleepy and do something about (by preference, take a nap), and avoid driving during normal sleep times (that dangerous midnight-to-6-a.m. time frame).

When it comes to driving, it’s a very short step from making good time to not making it at all.

Permanent link to this article: https://edwardwillett.com/2007/08/driving-under-the-influenceof-fatigue/

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