The Case for Addressing Operator Fatigue

Abstract

Sleep deficiency, which can be caused by acute sleep deprivation, chronic insufficient sleep, untreated sleep disorders, disruption of circadian timing, and other factors, is endemic in the U.S., including among professional and non-professional drivers and operators. Vigilance and attention are critical for safe transportation operations, but fatigue and sleepiness compromise vigilance and attention by slowing reaction times and impairing judgment and decision-making abilities. Research studies, polls, and accident investigations indicate that many Americans drive a motor vehicle or operate an aircraft, train or marine vessel while drowsy, putting themselves and others at risk for error and accident. In this chapter, we will outline some of the factors that contribute to sleepiness, present evidence from laboratory and field studies demonstrating how sleepiness impacts transportation safety, review how sleepiness is measured in laboratory and field settings, describe what is known about interventions for sleepiness in transportation settings, and summarize what we believe are important gaps in our knowledge of sleepiness and transportation safety.

Keywords: Biological rhythm, circadian; drowsiness; fatigue; homeostatic sleep-wake regulation; hours of work; individual differences; sleep inertia; sleep-wake propensity.

Figure 1. Accumulation and Dissipation of Homeostatic Sleep Pressure in Three Conditions with Varying Durations of Waking and Sleep

Horizontal axis: time; vertical axis: level of sleep pressure; shaded areas: sleep episodes; dashed horizontal line: typical level of sleep pressure accumulated at the end of a 16-hour waking day in someone who began the day fully rested. Upper panel-Normal condition: Sleep pressure accumulates during the 16 hours of waking and fully dissipates during the 8 hours of nocturnal sleep. Middle panel-Chronic Sleep Restriction: Sleep pressure accumulates during the 18 hours of waking to a level slightly higher than in the normal condition (indicated by the dashed horizontal line), but due to sleep being restricted to 6 hours per night, sleep pressure does not dissipate completely, leading the next waking day to begin at an elevated level; this process continues and sleep pressure keeps building up over subsequent days. Lower panel-Acute Sleep Deprivation: Sleep pressure accumulates to such a high level during the 24 hours of waking that the following 8 hour sleep opportunity is not sufficient to bring it back to baseline. Because this recovery sleep episode occurs during the daytime when the quality of sleep is reduced, this further limits the ability of this sleep episode to bring sleep pressure back to baseline levels.