Abstract: In order to quantify cascading failure in the urban road network with multiple nodes being in sudden congestion, and to solve the chain reaction caused by the congestion at important nodes, a network cascading failure model of double-layer network assignment is constructed. By calculating the degree of road network congestion to complete cascading failure simulation in this scenario, this phenomenon is analyzed. The geometric topology of network is first completed by primitive method, and the congestion nodes are deleted from the topology in turn. Then, the traffic efficiency of road network is measured by 3 robustness evaluation indexes:connectivity, the relative size of maximal connected subgraphs and the circle rate. Based on this, the maximum node failure rate under the condition that the traffic efficiency is no less than 10% is calculated. What's more, the congestion degree of road network in multi-node failure is worked out by using the double-layer network assignment model, and finally using Transcad 4.5 and Matlab 2012a, a medium-sized road network that owning 54 codes and 92 links is derived in Chengdu calculation and simulation. The simulation results show that in the most unfavorable conditions, the network's maximum failure node ratio is 19.3%; and the cascade failure caused by 2 more nodes' concurrent congestion will have more significant effect on road network capacity than the single node failure; and that the congestion level of the whole network tends will be stable when node failure surpasses 7, and gradually reaches the limit of network's robustness. The study is aimed at providing simulation technical reference for control measures under multi-node congestion in road network.

Key words: traffic engineering, cascading failure, congestion degree measure, multi-nodes failure, network simulation