Commodities are shipped under various constraints in a rail freight network to satisfy the shippers’ demands. An occasional disruption event may reduce the capacities of multiple network components and increase travel times through the paths that are still usable. These changes lead to increases in overall cost, even with optimal re-routing of freight flows. In this study we analyze the problem of finding the best sequence for restoring damaged components which minimizes the cumulative increment of cost during the restoration process beyond the cost in normal conditions (called “excess”).&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; A method is proposed for optimizing the restoration sequence of damaged components in a disrupted rail freight network. Given the network’s demand matrix and capacity settings, a mixed integer linear program (MILP) model is developed for routing freight flows and minimizing total hourly cost. The MILP problem can be simplified as a linear program (LP) in the actual solution process. The “excess” is computed for each examined restoration sequence in a disruption scenario, using the duration of each restoration step and minimized hourly costs in intermediate network states. A simple genetic algorithm (GA) is adapted for finding the restoration sequence that minimizes the excess after a disruption event. A numerical case with a small network and one disruption scenario is synthesized to demonstrate this method. For this small problem the optimized restoration sequence and schedule found by the GA is proved to be globally optimal through exhaustive enumeration. The GA’s effectiveness is further verified with three additional disruption scenarios. Sensitivity analysis shows that the minimized excess is more sensitive to capacities of damaged components when the capacities of network components or upper limits of travel time (before rail freight switches to trucks) are lower. It is also found that priorities for restoring damaged nodes increase at lower capacities of damaged nodes, higher capacities of damaged links, and higher unit cost of alternate shipment by trucks.&nbsp;&nbsp;

Optimized Sequencing of Post-Disaster Restoration Alternatives for Freight Railroad Networks

Paper Proceedings: https://asmedigitalcollection.asme.org/JRC/JRC2021/volume/84775

2021 Joint Rail Conference (JRC2021)

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