Stochastic Road Network Design Based On Vulnerability Analysis

The concept of road network vulnerability is concerned with potentials of network performance degradation or even network failures caused by various disruptions. Studies on road network vulnerability are of great significance for a better understanding of the coping capacity of the network and its operating performance when a devastating event happens. Currently, little attention has been paid to the application of vulnerability analysis in the planning and design of road networks. However, taking vulnerability into consideration when dealing with road network planning and design will contribute to a more scientific and rational way to allocate available resources, as well as a more targeted measure to improve the network, which is helpful in reducing the possible risk and making the network more robust and reliable.In this paper, a vulnerability-based road network design model which explicitly considers vulnerability as an important decision variable is proposed. Firstly, the concept of road network vulnerability is compared with the traditional concept of reliability and risk, the influencing factors of road network vulnerability are also proposed and analyzed. Based on the concept of network reserve capacity and network efficiency, two vulnerability indicators are proposed and applied in the identification of critical links in the network. The critical links identified with the proposed methods are also compared with those identified by traditional method based on volume to capacity ratio. At the same time, the influence of stochastic demand and stochastic link degradation level in the identification of critical links are considered. The difference in identified links shows that ignoring stochastic factors will result in a biased evaluation of network vulnerability. Finally, network vulnerability is introduced into road network design and a network design model with vulnerability constraints is built. A method combing genetic algorithm and simulation analysis is proposed to solve the proposed model. Two network design strategies based respectively on the improvement of critical links and non-critical links are developed and compared.The proposed network design model are tested with two case studies, results show that the vulnerability of road networks can be reduced by properly improving link capacities in the network. At the same time, under low or medium vulnerability-aversion conditions, reasonable results can be achieved by both of the two network design strategies with the proposed model. However, under high vulnerability-averse conditions, none of the method can be used to get a satisfied solution.