If you are driving on the highway next to an 18-wheeler that keeps drifting in and out of its lane, you have every reason to feel nervous.
There could be various reasons for the drifting, including sleepiness. At certain times of the day, there is a lull in the body’s circadian rhythm that can heighten truck driver fatigue.
About driver fatigue
Drivers of large commercial vehicles spend many hours behind the wheel. Although they should abide by state and federal regulations designed to limit driving time and enhance safety, some drivers ignore the regulations. They may take fewer rest breaks, sleep fewer hours and try to avoid fatigue with cups of coffee and opened windows. However, they cannot ignore their circadian rhythm.
Circadian rhythm issues
Every day and every night, the human body goes through a wake-sleep cycle called the circadian rhythm. The cycle affects the body’s internal clock and controls the level of alertness. Drowsiness occurs naturally between midnight and 6 am and again between 2 and 4 pm. These are the most dangerous times for any driver. A truck driver operating a big rig might succumb to lulls in the circadian rhythm. The result might be what you see—an 18-wheeler drifting in and out of its lane.
In a collision between a big rig and a passenger car or pickup, the smaller vehicle will almost always suffer the most damage and its occupants the most severe injuries. The Federal Motor Carrier Safety Administration studies the problem of driver fatigue and how best to combat it. FMCSA research shows that drivers are less alert after midnight. To avoid a safety-critical event, they must understand the value of sufficient rest. Respect for an inevitable circadian rhythm lull may help commercial drivers avert a disastrous crash.