1Traffic and Transportation Center, University of South Carolina, Columbia, South Carolina
The primary purpose of this investigation was to study and evaluate the relationship between highway sign brightness and alcohol impairment under night driving conditions. Sign brightness was controlled by varying the reflectivity of the signs and by employing both low and high headlight beam conditions. The data were collected under controlled conditions at night with the subjects actually driving the vehicle up and down the test track, which was approximately one and a half miles long and had signs mounted at 700-foot intervals. All of the signs were mounted on the right shoulder. The dependent measure was the correct reading distance. Three blood alcohol concentrations (BAC's) were investigated: sober, 0.08%, and 0.15%. Fourteen subjects completed the study and each subject participated on three separate nights. Each night was under a different BAC. Some of the subjects experienced difficulty in achieving and/or maintaining the 0.15% BAC. The actual observed overall mean BAC for the 0.15% BAC condition was 0.13%.
The results confirmed the experimental hypotheses that high reflectance signs significantly increase sign reading distance under night driving conditions and that alcohol impaired drivers require significantly brighter signs. Increases in both sign reflectance and headlight brightness yielded significant improvements in sign reading performance under all three BAC conditions. A significant interaction between the reflectance and headlight main effects indicated that the higher reflectance signs yielded a greater relative improvement in sign reading performance under low headlight conditions than under high headlight conditions. This is particularly important in light of the fact that previous research has indicated that approximately seventy percent of the nighttime drivers drive with low headlight beams.
A significant fatigue effect was noted under both the 0.08% and 0.15% BAC conditions. A significant interaction revealed the synergistic nature of the relationship between the effects of alcohol and fatigue on performance.