Each of twenty commercial motor vehicle (CMV) drivers participated in a single twenty-hour experimental session, during which they were continuously kept awake, but were allowed to ingest caffeine and use tobacco as they would in real-world conditions. Each participant drove in a fixed-base advanced driving simulator for approximately one hour on four occasions (at 9:00 am, 3:00 pm, 9:00 pm, and 3:00 am). The 59.5-mile (95.8-km) test route was designed with overpasses and intersections and changes in speed limits—to make the driving experience more like real-word driving. After the fourth drive, the participants were driven to the University of Minnesota’s General Clinical Research Center, where they slept for eight hours. The main result was that the steering performance of CMV drivers was impaired when they stayed awake for an extended period: There was a considerable increase in steering instability between the morning drive, at 9:00 am, and the nighttime drive, at 3:00 pm—an increase likely to have been produced by sleep deprivation. Other results were: (1) stopping behavior improved throughout the session—suggesting practice effects; (2) after the fourth drive, there was less reduction in the participants’ pupil size—but, since there was no difference in pupil size before the fourth drive, there was no evidence to suggest that pupil size reductions could be used to predict sleep deprivation; (3) data from other visual performance tests showed no effect of time of day; and, (4) results obtained from reaction time tests did not show decrements in performance—instead there may have been practice effects. (Author/publisher)
Abstract