Safety Analysis of Urban River-crossing Tunnels Based on VISSIM

The safety of river-crossing tunnels is an important aspect of urban road traffic systems. Previous studies concerning traffic safety mainly focused on urban roads. Given the absence of a number of variables, such as speed and real-time traffic volume, in traffic accident databases, the traffic safety of urban river-crossing tunnels has rarely been studied. This study used the microscopic traffic flow simulation software, VISSIM, to analyse the factors influencing the traffic safety of urban river-crossing tunnels. 12 simulation models based on 12 river-crossing tunnels in Shanghai were established. An exponential model for the speed standard deviation and accident rate was then constructed by calculating the speed standard deviation of the 12 tunnel models. Varied parameters of gratitude, speed limit, heavy vehicle ratio, and traffic flow characteristics were used to set different simulation scenarios in VISSIM. Results show that speed standard deviation is negatively correlated with gradient and heavy vehicle ratio, where a smaller gradient and fewer heavy vehicles are safer. Under different traffic volumes, the speed standard deviation first increases and then decreases with the increasing speed limit. From the perspective of traffic safety, a small speed limit is recommended; however, the number of passing vehicles per hour is reduced. Thus, a middle speed limit between 55 km/h and 60 km/h is recommended to balance the safety and efficiency of traffic. The findings in this study provide prospective information with which to optimize the design and operation of urban river-crossing tunnels.