Safety is a major concern for everyone who operates a vehicle, and the Federal Motor Carrier Safety Administration keeps up with issues that affect commercial truck drivers. Fatigue is one of those issues, and the circadian rhythm has a part to play in it.

The wake/sleep cycle

Circadian rhythm is the name given to the wake/sleep cycle that affects human beings. The cycle relates to the body’s internal clock. For example, people naturally become drowsy between 12 midnight and 6 a.m., and between 2 p.m. and 4 p.m. in the afternoon. The lull in the circadian rhythm that occurs during these hours becomes stronger if the body has had an insufficient amount of sleep.

The time-of-day issue

The FMCSA conducted a study about truck driver alertness. The findings indicated that time of day affects alertness level more than “time on task.” Commercial drivers are often on the road well after midnight, but the study showed they are less clearheaded at this time. For one thing, fatigue may be present after so many hours of driving. Truck drivers also fight the lull in their circadian rhythm, which may adversely affect their driving performance.

The dangerous first hour

Another study finds evidence that many truck crashes occur during the first hour of driving; that is, after the driver awakes from sleep. During that critical first hour, a driver may experience sleep inertia, which impairs cognitive functioning, reaction time, vigilance and short-term memory. The first hour of driving can easily occur in the early morning hours during the lull in the circadian rhythm.

In praise of a short nap

Crashes with big rigs account for more than 10 percent of all highway accident fatalities. The FMCSA advises drivers to take a nap when they feel drowsy and allow 15 minutes to become fully awake before getting behind the wheel. Drowsiness and lulls in one’s circadian rhythm can lead to a devastating crash.