Impacts of reduced visibility under hazy weather condition on collision risk and car-following behavior : implications for traffic control and management

Abstract

This paper examines the impacts of reduced visibility under hazy weather conditions on collision risk and car-following behavior to enhance the understanding of relationships among weather conditions, driving performance and road safety. A high-fidelity driving simulator is applied to collect vehicle trajectory data concerning a number of driving performance metrics under both clear and hazy weather conditions. The collision risks under different weather conditions as indicated by two surrogate measures – time exposed time-to-collision (TET) and time integrated time-to-collision (TIT) – are compared. Results indicate that hazy weather conditions have significant impacts on traffic safety in terms of increased collision risk and impaired car-following performance. The TET and TIT with a critical time-to-collision threshold value of 5 s under hazy weather conditions are 35.9% and 43.0% higher, respectively, than those under clear weather conditions. The increase in the low collision risk is more noticeable than that of the high collision risk. For car-following behavior, under hazy weather conditions, the average reaction time is higher and the sensitivity to the change in car-following spacing is lower. In addition, the interaction effects of vehicular speed on the relationship between weather conditions and some driving performance metrics are significant. Both the distance and time headways under hazy weather conditions are lower than those under clear weather conditions when the vehicular speed is high. However, no significant evidence is found for the relationship between weather conditions and distance or time headways when the vehicular speed is low or medium. Moreover, the variations in speeds under hazy weather conditions are higher than those under clear weather conditions when the speed is high or medium. The plausible causal relationships among the weather conditions, driving performance changes and collision risk are analyzed and discussed. Findings of this study contribute to the effective traffic control and management to enhance road safety under hazy weather conditions.