Research On Railway Distribution Node Layout For Urban Freen Logistics

In the process of social and economic development trend towards saving environmental protection and sustainable transformation,the logistics pays more attention to high-quality and green logistics development mode.Words such as low carbon,low pollution and high utilization rate have become increasingly familiar,which makes the serious traffic congestion,exhaust emission pollution and "three problems" caused by logistics distribution in the current city become precarious.Under the current situation of urban logistics distribution,railway is the main artery of China’s transportation,with rich railway resources,surplus transport capacity and other advantages.This provides a unique condition for vigorously promoting the transformation of the transportation structure of "road to rail",and also provides a huge advantage for its participation in urban logistics distribution.Of course,reasonable distribution node layout is the key to better and effective use of railway resources.Therefore,this paper starts from the railway’s participation in urban logistics distribution and takes the layout optimization of railway distribution nodes as the breakthrough point to carry out research.This can not only broaden the scope of logistics node layout optimization problem,but also lay a foundation for the further study of this problem in the future.Firstly,taking Chengdu city as an example,the paper analyzes the current situation of urban road traffic congestion,railway station capacity surplus,and the size and status of special lines.The feasibility of railway participating in urban logistics distribution is demonstrated from two aspects of internal conditions and external environment.This paper analyzes the elements of the sub-system from four aspects so as to improve the urban green logistics distribution system in which railway participates.Secondly,the paper analyzes the outward migration trend of urban logistics nodes and studies the distribution characteristics of logistics nodes in different periods,and summarizes the evolution form of logistics node layout along the urban industrial space and transportation axis.According to different classification criteria,the classification of nodes is distinguished,and the corresponding node hierarchy structure and classification method are proposed.On this basis,an appropriate distribution organization model is constructed according to the characteristics of different kinds of goods,and the distribution process and operation process of each stage of each kind of goods are analyzed in detail,which clears up the ideas for the construction of the following model.Thirdly,the combination of qualitative and quantitative methods is used to optimize the layout of railway distribution nodes in order to make the layout of nodes more comprehensive.By constructing comprehensive index evaluation system,AHP method and fuzzy comprehensive evaluation method are used to get the set of railway candidate points.On this basis,considering the disadvantages of railway transportation in timeliness and flexibility,a dual-objective optimization model with the lowest total cost considering the cost of carbon emission and the highest time satisfaction is established.The algorithm was optimized from coding mode,repair operation,dynamic mutation probability adjustment and initial feasible solution,and an improved NSGA-Ⅱalgorithm was designed to improve the solving efficiency.Finally,the case of Chengdu city is analyzed.Based on the selection of railway candidate nodes,the improved NSGA-Ⅱalgorithm was used to solve the example.Comparing to the unimproved NSGA-Ⅱ algorithm,the efficiency and Pareto solution set optimization degree of the improved NSGA-Ⅱ algorithm were analyzed.In the nine solution sets,four representative ones are selected to analyze the selection of alternative railway nodes,distribution of freight flow and spatial layout structure of railway distribution nodes,and relevant suggestions and countermeasures are put forward for the selection of schemes.This paper focuses on the optimization of railway distribution node layout within the city,which not only provides a new idea for urban green logistics distribution,but also broadens the research field for logistics hub layout optimization.Considering the time satisfaction into the objective function can make up for the disadvantage of railway transportation in timeliness,and promote railway participation in urban distribution to be better received by the logistics demander,which is also in line with the current actual demand.