Optimum Allocation Schemes On Buffer Time Of Train Diagram For Urban Rail Transit

The buffer time of train diagram for urban rail transit is designed to improve the absorption capacity of train to delay,the quality of buffer time allocation scheme directly affects whether passengers need to pay more additional travel time.Therefore,it is of great significance to deeply analyze the relationship between buffer time allocation and passenger delay and additional travel time,and then study the reasonable buffer time allocation scheme to improve the quality of train diagram and operation service level.This paper focuses on the optimization of buffer time allocation scheme of train diagram.On the one hand,it considers the positive benefits brought by buffer time allocation,that is,to improve the absorption capacity of train diagram to delay and reduce the total delay of passengers.On the other hand,the negative benefits of buffer time allocation are also considered,that is,it increases the additional travel time of passengers under normal circumstances.On this basis,a double objective optimization model is built to balance passenger delay and additional travel time.The main research contents of this paper are as follows:(1)The buffer time of train diagram for urban rail transit and the theory of delay propagation are analyzed.Firstly,the definition and classification of buffer time are introduced,and the operating principle of buffer time is analyzed.On this basis,the propagation mechanism of train delay is studied.The relationship between total train delay and primary delay and buffer time is deduced from the propagation of delay among stations and trains,and the approximate solution method is given;Then,the advantages,disadvantages and applicable scenarios of the existing buffer time allocation schemes are compared and analyzed.(2)Considering the absorption effect of buffer time on delay,the relationship between passenger delay and buffer time is analyzed,and the calculation formula of passenger delay is given.Under the condition of given total buffer time,the buffer time allocation model with minimum passenger delay is constructed,and the model is solved by genetic algorithm.(3)Considering the negative benefit of buffer time allocation,the relationship between passenger additional travel time and buffer time is analyzed,and the calculation formula of passenger additional travel time is deduced.Combined with the previously deduced passenger delay,a buffer time allocation model for balancing passenger delay and additional travel time is constructed,and NSGA-Ⅱ algorithm is used as the solution method of the model,and the algorithm is improved from the two aspects of congestion calculation formula and elite selection strategy to reduce the uneven spatial distribution of algorithm solutions and falling into local optimal solution.(4)The case study is based on a rail transit line.The results show that the application of the buffer time allocation model with minimum passenger delay can effectively alleviate the impact of knock-on delay.The buffer time allocation tends to the sections with large cross-section passenger flow and stations with large passenger flow,and the difference in the distribution of passenger flow in the up and down directions will lead to different fluctuations in the buffer time allocation;Using the buffer time allocation model for balancing passenger delay and additional travel time,the optimization results achieve a good balance between passenger delay and additional travel time,and the Pareto solution set can be used as the basis for determining the buffer time allocation scheme.