Another factor is the time of day. We have two distinct lulls in our level of alertness which are referred to as circadian dips. The weaker of the two occurs between 14:00 and 16:00. The stronger dip in alertness, and most important in terms of accident rates, is between 02:00 and 05:00. The NTSB demonstrated that sleep-deprived drivers, as defined by less than six hours of sleep, were 5.6 times more likely to be involved in an accident between 02:00 and 05:00.
Medications are another factor that can predispose you to sleepiness. Some of the older allergy medications such as Benadryl (diphenhydramine) can make you sleepy. The same applies to pain medications that contain codeine, hydrocodone, or oxycodone. Other culprits are muscle relaxants such as Flexeril (cyclobenzaprine) and anti-anxiety medications such as Valium, lorazepam, and clonazepam. All of these have potent sleep-inducing side effects.
Finally, sleep apnea is a major problem. Recent studies done by the Federal Motor Carrier Safety Administration have demonstrated that the incidence of sleep apnea in truck drivers is 17% to 28%. This is way above the national average. Increased weight and age above 50 are predisposing factors, as is a neck circumference greater than 16 1/2 inches. Several studies have demonstrated that drivers with undiagnosed sleep apnea have a two to seven times higher risk of falling asleep behind the wheel, as well as an increased chance of diabetes, hypertension, stroke, and heart attack.
So what can you, the driver, do to decrease this problem? First of all, try to ensure that you get at least seven hours of sleep the night or day before you drive. Second, you can also take advantage of the power of napping. We find that a two hour nap before your shift can be quite helpful in maintaining alertness. A 20 to 30 minute nap during your shift and before you are sleepy can go a long way to keeping you alert while driving. Be mindful that longer naps can leave you groggy and be counterproductive.
You should be aware of your prescription and nonprescription medications. Familiarize yourself with their sleep-related side effects. If unsure, ask your health care provider or your pharmacist.
If you are having trouble staying awake, feel fatigued all the time, snore, are overweight, or have a neck greater than 16 1/2 inches, discuss this with your health care provider. There is a high likelihood you might have sleep apnea. The good news is that with treatment your sleepiness should resolve and your driving performance should return to normal.
The bottom line is that the accident rate among professional truck drivers is very much related to sleepiness and fatigue. In fact, by adopting measures such as my colleagues and I have recommended, I am certain that we will see a major drop in their occurrence.
Robert S. Rosenberg, DO, FCCP
Board Certified Pulmonary and Sleep Medicine
Sleep Disorders Center of Prescott Valley
Sleep Disorders Center of Flagstaff