Exploring the Effects of Variable Speed Limit on the Car-Following Process on Bridges in Fog with Consideration of Human Factors

Abstract

Fog is a critical risk of river-crossing bridges. Setting a reasonable speed limit is essential to ensure safe operation when driving on river-crossing bridges in foggy conditions. According to the existing variable speed limit (VSL) strategy, this study takes the E’dong Yangtze River Bridge in China as an example to conduct driving simulation experiments and clarify the influencing factors of the car-following process for a foggy bridge under different speed limit conditions. Based on human factors, this paper uses the generalized linear mixed model (GLMM) to quantify the impact of different speed limit strategies and driver attributes on the car-following process of foggy bridges, considering the random effect caused by driver heterogeneity. The indicators related to operation characteristics (represented by longitudinal fluctuation and vehicle’s compliance) and car-following behaviors are selected to evaluate the car-following performance. The results reveal the following five findings: (1) Speed limit strategies and driver attributes significantly affect the car-following process, thereby changing operation characteristics and car-following behaviors. Their impacts on the car-following behaviors are more significant than that on the operation characteristics. (2) A low-speed limit can significantly improve drivers’ car-following behaviors and better meet the visual needs of the leading vehicle, which is conducive to improving safety. (3) Males have a lower visual need for the leading vehicle during following and are less sensitive to the distance between vehicles. (4) Professional drivers can more comfortably adjust the car-following state according to the leading vehicle. (5) If the speed limit is high, drivers often tend to sacrifice the visual need of the leading vehicle in exchange for a larger distance to ensure safety. This study contributes to optimizing the VSL strategy for foggy bridges and providing management departments with a foundation to implement more effective speed limits to reduce driving risks.