Demand assignment for express delivery in high-speed railway networks:A passenger train delivery mode
Aiming at the optimization of demand transportation and assignment in the express delivery network with high-speed railway,this paper proposes a two-stage demand assignment method under the passenger train delivery mode.In the first stage,we use the K-shortest al-gorithm to calculate the set of feasible transportation routes for freight demands.In the second stage,an optimization model for network train demand assignment plan is built by introducing the type of demand transportation path,train loading state and train cross line operation.In addition,due to the complexity of combinatorial optimization problems and the nonlinear and multivariable characteristics of the model,the traditional particle swarm optimization algorithm has low efficiency in solving transportation and assignment plan models under different freight scales.Therefore,this paper proposes an improved nested particle swarm optimization algorithm to improve the efficiency and accuracy of the solution by iteratively optimizing the transportation path and demand assignment plan.Finally,the paper takes the high-speed railway and EMU operating network composed of 10 lines,including Harbin Dalian Railway,Beijing Shenyang Railway,Changchun Baicheng Wulumuqi Railway,etc.,as an example to verify the demand assignment model and the effectiveness of the algorithm.The experimental results indicate that the optimization model for the transportation and assignment plan considering the operation of cross-line trains reduces the demand backlog by 5%approximately.In addition,the nested particle swarm optimization algorithm can effectively solve the demand transportation and as-signment problem for large-scale high-speed railway networks,and the efficiency of the solution is improved by about 20%compared with the classical algorithm.