Study On Optimization Of Railway Express Freight Transportation Considering Different Timeliness Requirements

With the development of national economy and the continuous improvement of people’s living standards,people choose the mode of goods transportation from the previous freight rate priority to ensure the safety and timeliness of goods transportation,resulting in an increasing number of express goods transportation.Because the travel time of goods under the traditional "scattered express organization mode" is mainly limited by assembly and waiting,and the station operation process under this organization mode is relatively fixed and there is little room for optimization,this paper focuses on the optimization of high-speed rail express freight transportation.At present,the research on the express freight transportation mode of high-speed rail is mainly based on the "point-to-point" direct transportation under the mode of passenger car piggyback and the transportation organization mode with loading and unloading operations on the way.The "point-to-point" direct transportation mode requires that the loading and unloading stations of express goods are consistent with the departure stations of high-speed trains,which makes the high-speed trains that express goods can choose more limited;At the same time,the train no longer carries goods at the way station,resulting in the virtual capacity of the train.Although the high-speed rail express freight piggyback transportation mode with loading and unloading operations on the way improves the capacity utilization rate of the train,this transportation organization mode will produce a large cross between passengers and goods,and at the same time,it requires high cooperation between station staff and train attendants,which increases the difficulty of transportation organization.In this regard,this paper puts forward the "terminal unloading" transportation organization mode under the high-speed rail piggyback organization mode.Under this mode of transportation,high-speed trains piggyback express goods at the starting station and stops along the way,with the final arrival of the train as the unloading station,which not only improves the piggyback ability of high-speed trains;At the same time,there is no cargo unloading operation at stations along the way,which reduces the working pressure of passengers and goods crossing and field staff.Based on this,this paper has done the following work for railway express freight transportation: The main results are as follows:(1)The advantages and disadvantages of five different modes of transportation organization of high-speed rail express are analyzed,and the advantages and disadvantages of "point-to-point" direct transportation and transportation organization with loading and unloading operations along the way are compared in view of the current mainstream mode of high-speed rail passenger car piggyback,and the basic model of vehicle-cargo matching under the two modes of transportation organization is constructed.(2)Aiming at the shortcomings of the existing transportation organization mode under the piggyback mode of high-speed rail passenger cars,an improved transportation organization mode of "unloading at the end" is put forward.This paper analyzes the process of vehicle-cargo matching under the organization mode of "terminal unloading" by using a two-layer spatiotemporal network.Under the constraints of comprehensive consideration of different timeliness requirements of express cargo,transportation requirements of stations,piggyback capacity of buses,utilization rate of piggyback capacity of buses and train stop schemes,a vehicle-cargo matching model under the organization mode of "terminal unloading" is constructed with the objectives of shortening the overall travel time of express cargo and minimizing the crossing times of passengers and goods as much as possible.(3)An adaptive NSGA-II algorithm is designed.In the process of algorithm optimization,the probability of crossover and mutation changes with iteration times and iteration results in real time,which effectively prevents the destruction of the optimal solution caused by blind crossover and mutation.At the same time,in the process of congestion calculation,the objective function is unified by orders of magnitude,which improves the operation efficiency of the algorithm.(4)The reliability of the model and the feasibility of the algorithm are verified by taking the high-speed rail piggyback transportation of "Arrival on the same day" freight products on some sections of Xu-lan high-speed railway and Beijing-Shanghai high-speed railway as examples.Compared with "point-to-point" direct transportation,"terminal unloading" organization mode reduces the travel time of goods and improves the efficiency of fast freight transportation under the same number of stops;Compared with "point-to-point" direct transportation,"terminal unloading" organization mode improves the utilization rate of bus piggyback capacity.High-speed rail freight transportation is the development trend of railway freight transportation in the future,which is the inevitable requirement of the development of the times and the reform of freight market.The organization mode of "unloading at the end" studied in this paper has certain reference significance for the existing high-speed rail piggyback transportation organization and the future high-speed rail freight train transportation organization.