Optimization Approach to Track Capacitated Train Assembly Shunting Problem with Sequence Partition Requirement Based on Bitstring
Assembly shunting is one of the main daily operations in railway stations.Studying optimization approaches to this operation plays an important role in improving the efficiency of assembly shunting operations and transportation pro-duction quality of stations.This paper studied the shunting problem of assembling one inbound train into one outbound train with sequence partition requirement(SRP)under limited number and capacity of shunting tracks.By extending the existing shunting principle based on bitstring,two 0-1 matrices were used to accurately encode a valid assembly shunting operation plan with SPR.A full-track bitstring method and a reserved-track bitstring method were designed respectively.In the former,all shunting tracks were pulled out in a round robin sequence,while in the latter all shunting tracks ex-cept for the train formation track were pulled out in a round robin sequence.A unified two-stage computing approach,which minimized the numbers of pullouts,shunting railcars,occupied shunting tracks and roll-ins in a lexicographic or-der,was developed for the two bitstring methods.In the first stage,given the number of pullouts and the set of available shunting tracks,a 0-1 linear programming model with the objective of minimizing the number of shunting railcars was formulated to find the two valid matrices.The model was iteratively solved by gradually increasing the number of pullouts and reducing the set of shunting tracks,until preset conditions were met.In the second stage,three rules were custom-ized to reduce further the numbers of shunting railcars and roll-ins of the valid matrices obtained in the first stage.A set of instances designed by existing assembly shunting methods were collected to verify the superiority of the proposed shun-ting method to existing methods.
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