The Economic Value of Reserve Capacity Considering the Reliability and Robustness of a Rail Transit Network

Existing studies estimate the economic value (EcV) of network reliability and robustness separately. In this study, a model is proposed for estimating the EcV of reserve capacity in a rail transit network (RTN), which consists of: (1) the reduction of passengers' total generalized travel cost (GTC) in normal operations, (2) the EcV of reliability enhancement in normal operations, and (3) the EcV of robustness enhancement when disturbances occur. The standard deviation of travel time (SDT) is used to measure travel time reliability (TTR). The reserve capacity helps to reduce passengers' total GTC and the SDT during normal operations. The EcV of reliability enhancement equals the EcV converted from the reduction in SDT when the RTN operates normally. The EcV of robustness enhancement is the difference of passengers' total GTC with and without reserve capacity when disturbances occur. To optimize reserve capacity, a model is developed to maximize its net benefit, equaling its EcV minus its cost, which is then solved with a quantum genetic algorithm. A case study of Chengdu's RTN shows the effectiveness of the model with promising numerical results. The research findings show that the value of reserve capacity is severely underestimated without considering the EcV of reliability and robustness. The study can guide policymakers and operators in quantifying the EcV of reliability and robustness enhancement when expanding an RTN's capacity.