The supreme goal of railway express freight transportation is to meet the various demands of shippers. This paper considers the optimization problem of the operation plan for express freight trains based on shipper demands, including transport volume, service frequency, and transit time. An integer programming model that takes maximum shipper demands as optimized objective is proposed to realize the assignment of trains to candidate paths. In this model, the number of marshalling cars for express freight train is set as a decision variable rather than a constant to better satisfy the demand characteristics. A heuristic solution algorithm based on genetic algorithm is then designed. Finally, a numerical case is applied to verify the feasibility of the model and the algorithm. 1. Introduction Express freight has an important role in the whole freight transportation system. With the constant increase in energy cost, the increasing seriousness of traffic congestion, and environmental pollution, the express freight transportation system that takes aviation and expressway as the main modes reflects many problems [1]. Many countries have paid more attention to the development of rail express freight transportation, which is more energy-saving and environment friendly [2]. Being the foundation of the railway freight transportation organization, operation plan of express freight trains is to determine the set of trains to satisfy the express freight demands. Compared with bulk freight, express freight has the characteristics of small batch, excellent timeliness, and high value, and the shippers have higher requirements on service quality, but lower sensitivity on the transport cost. Consequently, the characteristics and shipper diversified demands of express freight should be considered when determining and optimizing the train operation plan. In the past decades, various attempts have been made to gain optimal transportation scheme for railway express freight demands. These attempts mainly involve three kinds: design of formation plan for direct freight trains, service network design of express freight, and determination of operation plan for express freight trains. Formation plan of direct freight trains determines the transport scheme of car flows by direct trains, including direct trains in the loading place and the technical station [3]. Many express freight trains are direct trains, and freight demands can be converted into car flows; thus, its determination method can provide references for the optimization of operation plan for express trains. Lin et al.
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