Real-time Vulnerability Analysis of Urban Expressway

This study proposes a new method for evaluating the road network vulnerability per unit time: the real-time vulnerability index (RVI). The practical application of the proposed measure in real traffic scenarios is investigated by using empirical data from Shanghai Expressway.To prevent traffic congestion, a critical threshold of RVI (RVI*) is suggested for traffic control. Furthermore, the hysteresis on macroscopic fundamental diagram (MFD) and RVI is further analyzed in the phase transition of traffic states. The results show that RVI can help derive some representative traffic characteristics in real time and dynamically reflect road network vulnerability: when traffic congestion or accidents occur on the road network, the results observed for the traffic hysteresis on MFD and RVI were consistent, and RVI is easier to observe and more suitable for traffic management. The findings prove that RVI is a reliable indicator to help predict the dynamic operation of the road network.