Date of Award

Spring 2012

Document Type


Degree Name

Doctor of Philosophy (PhD)



Committee Director

Bryan E. Porter

Committee Member

James Bliss

Committee Member

J. Catesby Ware

Committee Member

Elaine Justice


Sleepiness causes performance decrements that lead to thousands of crashes and fatalities annually. Research supports the conclusions that sleep duration and circadian rhythms impact sleepiness and affect driving performance. Conflicting in the literature is whether severity of sleep disorders, sleep quality and subjective sleepiness affect driving performance. The correlation between a driver's perception of their sleepiness and their driving performance is also unclear. The primary goal of this study was to create an in-depth model demonstrating which measures of sleepiness influence driving performance. It was hypothesized that sleep quality, sleep apnea severity and subjective sleepiness add to a model of how sleep constructs impact driving performance. The secondary goal of this study was to compare trait and state sleepiness to determine which correlates with driving performance. It was hypothesized that participants with state sleepiness would have a greater decline across the 60-minute drive as compared to participants with trait sleepiness. Both sleepiness groups would have increased lane position variability compared to the normal group. The tertiary goal was to examine driving performance decrements of sleep apnea drivers compared with healthy controls. It was hypothesized that the sleep apnea group would perform worse on the driving simulator test compared with the control group.

Results indicate that sleep quality and subjective trait sleepiness significantly add to models of sleepiness and driving performance. The model developed here show that years with driver's license, sleep efficiency and trait sleepiness are significant predictors of lane position variability. Also, results show that driving performance is worse for participants high in trait sleepiness. Participants with high state sleepiness had no significant performance differences compared to non-sleepy participants. Sleep apnea participants did not perform significantly worse than controls as hypothesized but there was a significant group by time interaction indicating that sleep apnea participants' performance degraded more quickly over the course of the drive. These results can be generalized to the community members and students, but not necessarily to sleep disorder center patients.


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