Study On The Calculation Model Of Urban Rail Transit Line Construction Sequence In Time

China is in the period of rapid development of urban rail transit planning and construction,and more and more cities regard urban rail transit system as the best option to solve urban traffic problems.In actual engineering projects,the excessively advanced operation of the line will lead to shortage of passenger flow and poor operation efficiency.The delay of the line operation will lead to the failure to meet the demand of passenger flow and limit the development of the city.These problems are related to the unwise decision of sequence in time of line construction.The construction process of the urban rail transit system has the characteristics of large engineering volume,long time span,and large investment in resources so that the scale of the lines that can be built during a construction period is limited.It is necessary to arrange reasonable sequence in time of each line under the conditions of meeting the needs of urban passenger flow and meeting the constraints of urban economic capacity.The actual project generally determines construction sequence in time through qualitative analysis,and the results are often inaccurate due to subjective factors.There are many factors that affect sequence in time of line construction,and it is difficult to qualitatively analyze the impact of various factors.Therefore,it is necessary to study the method of quantitatively calculating the sequence in time of line construction by integrating all factors to make the decision result objective and reliable.This paper divides the sequence in time of the urban rail lines construction problem into two levels: construction sequence and construction timing,and establishes a quantitative calculation model for line construction sequence and a quantitative calculation model for line construction timing.When we know the sequence and timing of line construction,we know the sequence in time of construction of each urban rail line.The main research contents and results of this paper are as follows:(1)This article establishes a quantitative index system for line construction sequence decision-making.This paper analyzes the main factors that affect the sequence of line construction and divides them into four categories: passenger demand,transportation services,network structure and urban development.Daily passenger flow intensity,daily turnover and maximum cross-sectional passenger flow in single peak hour are proposed as representative quantitative indicators of passenger demand.Traffic location coefficient and coverage of passenger centers are proposed as representative quantitative indicators of traffic services.Contribution of network reachability is proposed as a representative quantitative indicator of network structure.And Position coefficient is proposed as a representative quantitative indicator of urban development.(2)This article establishes a quantitative calculation model for the sequence of line construction.The multi-attribute decision-making method TOPSIS method is studied and its limitations are improved.A quantitative calculation model for the sequence of line construction is established based on the improved TOPSIS method.The comprehensive construction priority of the line is determined by calculating the weighted Euclidean distance between each line and the sequential ideal solutions.A complete algorithm is designed and the program calculation is implemented in Python.(3)A quantitative calculation model for the timing of line construction is established.By studying the development process of the network scale of typical cities,it is found that its change over time shows an S-shaped trend.Various S-shaped curve fitting results show that the logistic curve can describe the process stably and accurately.The reasonable growth curve function expression of the network scale that meets the urban development needs and the constraints of construction capacity is determined.A calculation model for the timing of line construction with constraints of line construction sequence,line length and scale growth curve is established to calculate the end and start time of line construction.A complete algorithm is designed and the automatic calculation and the visualization of the results are realized in Python.(4)Taking Line 1 ? Line 15 of the Chengdu Urban Rail Thansit as an example,the construction sequence and timing are calculated by the two-layer model proposed in this paper.It is found that the construction sequence of Line 7 is too late,and the construction sequence of Line 10 is too front.The timing of construction of the phase 1 of Line 1 lags about 2.25 years,and phase 2 of Line 1 lags about 2 years and phase 2 of Line 2 lags about 1.5 years.The timing of construction of the phase 1 of Line 2,phase 1 of Line 4,phase 1 of Line 3,phase 2 of Line 4 and phase 1 of Line 10 lags about a year.The timing of the construction of Line 7,phase 3 of Line 1,phase 2 of Line 3,Line 5 and phase 2 of Line 10 is reasonable.