Study On Optimization Of Railway Express Cargos Service Network Design Based On Timeliness

China’s social and economic development is stable and positive,and the industrial structure is gradually adjusted and optimized to the manufacturing and service industries,which in turn affects the freight demand structure and the transportation demand for express cargos continues to increase rapidly.Express cargos transportation pays attention to the quality of transportation service.In the process of enhancing the attraction of express cargos,it encourages transportation enterprises to continuously improve the quality of transportation service from the whole process of cargo transportation.In recent years,the level of railway facilities and equipment in China has been continuously improved,and the supply capacity of railway transportation has reached a new level.Under this background,how to make full use of railway transportation resources,optimize the transportation organization process,and realize the safe,reliable,convenient and fast transportation of express cargos is a severe challenge faced by China’s railway transportation department.The high timeliness requirement is an important feature of express cargos,and the guarantee of timeliness is also an important manifestation of railway transportation service level.Therefore,this paper focuses on the optimization of the transportation service network design for the timeliness of railway express cargos,and provides support for railway freight product supply optimization,mainly including the following aspects:(1)According to relevant literatures at home and abroad,the definition and characteristics of railway express cargos are described,and the composition of its transport time is described based on the transport process.Then,this paper analyzes and summarizes the research content of service network design problem,and focuses on the characteristics of existing models and solving algorithms.Therefore,this paper put forward the idea of service network design considering timeliness of railway express cargos.(2)Considering the restrict relationship among express flows demand,physical network and service network,this paper respectively established frequency service network design model and dynamic service network design model.The constraints including due transport time constraint,service arc capacity constraint,segment capacity constraint of physical network,logical relationship constraint between decision variables and flow equilibrium constraint.The objective function of models in this paper is to maximize transportation benefit,it can balance the demand of transportation enterprises and the shippers.(3)In this paper,a method of determining alternative path set combining k-short path algorithm and circuitous rate is proposed.Building a model on the basis of alternative service set obtained according to service design strategy can reduce the difficulty and scale of solving the model.Especially in the dynamic model,the alternative service arcs can be used to select the time period of providing transportation service,so that the comprehensive optimization of direct service and transit service can be considered without excessive expansion of solution scale.In order to improve the solving efficiency,the linearization method for the nonlinear model in this paper is also proposed,so that the optimal solution can be obtained easily.(4)Finally,the Gurobi software with excellent performance is invoked by Python programming language to solve the numerical example in this paper.It proves that the model can optimize the train service type,running frequency,transportation route and flow distribution scheme simultaneously,and get the reasonable transport service network design results,which can provide support for the further detailed train operation scheme.This paper includes 28 figures,18 tables and 76 references.