Interactive driving simulators have provided a safe and efficient mechanism for studying the effects of impairing agents on driving performance. Unfortunately, in the past simulators have been limited in their ability to test drivers for long periods of time. In this study the authors developed a methodology for testing drivers over a two hour time period; and for analyzing the possible effects that this long driving period had on driving performance. This paper presents the basic results of this portion of the study, and discusses the effects of alcohol and fatigue on driver performance variables which may lead to accident involvement.