Comprehensive optimization of the one-block and two-block train formation plan

Different from the traditional multi-step train formation plan optimization, which generates the one-block train formation plan firstly and then combines some one-block trains to form two-block trains, this paper presents a comprehensive optimization model which considers the one-block train and two-block train simultaneously. The model consists of three sub-problems: shipment routing, shipment-to-block assignment and block-to-train assignment. The objective of this model is to deliver all of the commodities with the minimum car-hour consumption at the technical yards while satisfying the network capacity constraints. A heuristic optimization approach based on the ant colony system is proposed to solve the model. The test results based on practical examples in northeast China railway network show that the one-block and two-block train formation plan obtained by using the comprehensive optimization model and approach proposed in this paper can significantly reduce the total car-hour consumption at the technical yards compared with the train formation plan which only uses the one-block train. The comprehensive optimization can achieve better results than the traditional multi-step optimization.