Economic evaluation of redundancy design for transportation networks under disruptions: Framework and case study

Abstract

Adding transportation network redundancy is an effective strategy to hedge against disruptions in the pre-disaster planning stage. However, given the low frequency of disruptions and large financial cost of redundancy design, the economic feasibility of redundancy design has always been challenged. This paper develops a framework to investigate the economic feasibility of adding redundancy to road networks in the pre-disaster planning stage by considering network-wide benefits and stochastic disruption scenarios. Specifically, the redundancy of road networks is defined as route diversity, which refers to the number of behaviorally alternative routes between each origin-destination pair. The redundancy design schemes are formulated by adding parallel links to critical links in current road networks, as these added links provide alternative routes for numerous travelers when the critical links are disrupted. As the redundancy of a transportation system is not only accessible under disruptions but also on duty in normal states, this paper estimates the benefits of redundancy design for road networks in both normal and disruptive states. The Winnipeg network is then used in the case study with the focus on adding redundant bridges. Results indicate that the benefit-cost ratio (BCR) of adding one redundant bridge is 3.51 and redundancy design in road networks is economically feasible. Since the value of BCR is sensitive to the discount rate and the performance of disruptive events, the related data should be collected cautiously when estimating the benefits of redundancy design in practice. Meanwhile, we observe the diminishing marginal effect in the addition of multiple redundant links, which provides insights into the decision-making regarding the optimal amount of redundancy investment in road networks. The proposed framework can be considered as a decision support tool to justify and rank alternative projects from the new perspective of redundancy and resilience.