Dynamic Assessment Of Road Network Vulnerability Based On Cell Transmission Model

The operation state of road network maintaining stable and orderly so as to resist adverse events is critical for guaranteeing urban traffic function and regular schedule of residents.Researching on road network vulnerability,identifying the vulnerable links and amending them will strengthen the ability of road network resisting disturbances.Vulnerability research under static condition lacks the consideration of dynamic evolution process of traffic flow,thus cannot exactly reflect the dynamic variation process of vulnerability.Based on the cell transmission model,this paper closely combines the road network vulnerability assessment with the traffic flow evolution process,and expands the evaluation results of road network vulnerability from the perspective of time dimension.Traffic flow evolution process under the disturbance is divided into several phases.The dynamic characteristics of road network vulnerability are discussed from the aspects of disturbance and traffic flow evolution respectively.As for traffic congestion in the chaos phase,the dialectical relationship between traffic congestion and road network vulnerability is discussed.The cell transmission model which is competent to simulate the impact of disturbance and traffic evolution process is determined as the basic model.According to the dynamic characteristics of traffic flow,the cumulative index and time-varying index of vulnerability assessment are established from the viewpoint of traveler time loss.Considering the impact of disturbance on vehicle routing,the dynamic traffic assignment model is improved to a modified one based on link selection with dynamic user optimal principle.By introducing vehicle evacuation method to the accident link,the cell transmission model is modified.The model efficiency is optimized to simulate the dynamic evolution process of traffic flow.Combining traffic flow model with vulnerability index,the road network vulnerability assessment model is established.A case study on Bao’an Central District of Shenzhen is conducted.Combining with the traffic flow parameters’ variation trend,the cumulative vulnerability and time-varying vulnerability are analyzed from the aspects of road network and each individual link under the condition settings of different disturbance location and various impact degree.The results reveal that chaos phase and relief phase do exist in the evolution process of road network vulnerability,and vulnerable links in each phase can be exactly identified by the model.