Effects of Alcohol and Fatigue on Driving Performance in Different Roadway Geometries

Experiments were conducted with a driving simulator to examine how different blood alcohol concentrations (BACs) and fatigue levels influenced driver safety performance in various roadway geometries. Each of the 22 participants completed five drives. The control condition, serving as the benchmark in the five drives, refers to driving under sober conditions. The four testing conditions included drives with three BAC levels (0.02%, 0.05%, and 0.08%) and drives in a fatigued state. The experimental test scenarios covered both straight and curved roads. The tangent straight roadway segments were used to connect the curved ones of three different radii (200, 500, and 800 m) in both travel directions. Statistical analysis of result variance was used to quantify the effectiveness of measures of vehicle longitudinal speeds and lane positions. The averages and standard deviations of speeds and lane positions, indicated as SP_AVG, SP_SD, LP_AVG, and LP_SD, were all significantly affected by drivers’ states. Experimental test results indicated that different levels of BAC and fatigue imposed different influences on driver safety performance. Road geometric characteristics, such as radii and curvature directions, had significant impacts on drunk and fatigued drivers’ capability of manipulating vehicles for safe operations. The research findings provide reference information to identify hazardous driving status, such as drunk and fatigued driving under different geometric conditions.