Sleepiness plays an important role in major crashes of commercial vehicles. Because determinants are likely to include inadequate sleep and sleep apnea, we evaluated the role of short sleep durations over 1 wk at home and sleep apnea in subjective sleepiness (Epworth Sleepiness Scale), objective sleepiness (reduced sleep latency as determined by the Multiple Sleep Latency Test), and neurobehavioral functioning (lapses in performance, tracking error in Divided Attention Driving Task) in commercial drivers. Studies were conducted in 247 of 551 drivers at higher risk for apnea and in 159 of 778 drivers at lower risk. A multivariate linear association between the sets of outcomes and risk factors was confirmed (p Ͻ 0.0001). Increases in subjective sleepiness were associated with shorter sleep durations but not with increases in severity of apnea. Increases in objective sleepiness and performance lapses, as well as poorer lane tracking, were associated with shorter sleep durations. Associations with sleep apnea severity were not as robust and not strictly monotonic. A significant linear association with sleep apnea was demonstrated only for reduced sleep latency. The effects of severe apnea (apnea-hypopnea index, at least 30 episodes/h), which occurred in 4.7%, and of sleep duration less than 5 h/night, which occurred in 13.5%, were similar in terms of their impact on objective sleepiness. Thus, addressing impairment in commercial drivers requires addressing both insufficient sleep and sleep apnea, the former being more common.Keywords: commercial drivers; excessive sleepiness; obesity; obstructive sleep apnea; sleep durationIn the United States, approximately 5,600 people are killed annually in crashes involving commercial trucks (1). Falling asleep while driving is an important factor in serious crashes involving commercial vehicles (2, 3), prompting the question, why? There are likely to be at least two mechanisms. The first is chronically insufficient sleep, that is, excessive sleepiness and performance impairments from accumulating sleep debt when individuals curtail the duration of their sleep day after day (4-6). Short sleep durations have previously been described in commercial drivers (7). The second mechanism is obstructive sleep apnea, which has been found to be common in commercial drivers (8, 9). This study was conducted to assess the relative role of these risk factors for impairments in commercial driver's license holders. Daytime sleepiness and performance were assessed using neurobehavioral tests relevant to the driving task. These were evaluated relative to laboratory measures of sleep-disordered breathing and objective estimates of sleep duration at home. There are currently no published data to guide policy and decision makers regarding performance assessment, or regarding factors associated with impaired performance in drivers of commercial vehicles. The results presented in this article have previously been reported in abstract form (10, 11). There has also been a publication, using data collect...

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