Sleep deprivation affects a driver’s ability to safely operate a motor vehicle by increasing the likelihood that a driver will fall asleep at the wheel, increasing the number of microsleeps, increasing reaction time, degrading attention and vigilance, increasing distractibility and confusion, decreasing motivation, and increasing the probability of driving performance errors. With respect to mood, sleep-deprived people may experience irritability, forgetfulness, and aversion to effort. In other words, sleep deprivation not only affects a person’s alertness, it also affects critical cognitive processes required to drive a vehicle. For this reason, accidents caused by sleep deprivation are likely not the result of decreased alertness alone.

Factors Leading to Drowsy Driving

Research indicates that the time of day is the most important factor contributing to driver fatigue and alertness levels, with drowsiness episodes being eight times more likely between midnight and 6 am than during other times. One study revealed that drivers have a 20-times higher likelihood of falling asleep behind the wheel at 6 am compared to 10 am. Long-distance truck drivers working overnight or early morning shifts are particularly susceptible to sleep deprivation due to disruptions in their natural sleep patterns. Factors such as total sleep duration, timing of sleep, sleep quality, environmental conditions (e.g., darkness, monotonous driving), underlying medical conditions (e.g., sleep apnea), and drug use (e.g., methamphetamine, sedating medications) also contribute to fatigue.