Research On Bottleneck Identification Method Of Urban Rail Transit Network

With the continuous growth of the national economy and the steady progress of the urbanization,our country’s urban rail transit network construction has entered a new stage of rapid development.The rail transit of major cities in our country has been opened from single line to multiple lines and gradually formed into a network.Network operation has greatly improved the capacity and volume of transportation.However,as the network becomes more complex,the passenger flow volume increases and its temporal and spatial distribution is unbalanced,the urban rail transit network has uncoordinated and mismatched the supply and demand of transportation capacity,the state of service level fluctuates,and other issues.The overall capacity enhancement and service level improvement are usually limited to certain stations or sections.Accurately identifying these key stations and sections is an important part of urban rail transportation planning and management,and it is also a prerequisite for the rational utilization and improvement of overall transportation efficiency,which is conducive to accurately grasping the new requirements of the network operation situation.This article aims to study the theories and methods of urban rail transit network transportation supply and demand analysis,network bottleneck identification,and bottleneck elimination that are suitable for the characteristics of urban development and rail transit construction and operation in our country.First,analyzing the three elements of network: structure,capacity,and passenger flow;leading to the definition of network bottleneck.The urban rail transit network is divided into three levels of "physical structure network","capacity supply network" and "passenger flow demand network".Constructing the network model based on the Space L method.Analyzing the network structure,network system capacity and network passenger flow characteristics.Comprehensively considering the structural characteristics,capacity characteristics,passenger flow characteristics and service characteristics of the network,to define,classify and analyze the bottleneck of the urban rail transit network,mainly including static bottlenecks and dynamic capacity and service bottlenecks,for making the targets of identification clear.Taking the static bottleneck with high importance of network structure and low capacity deployment as the object,a bottleneck identification method based on Complex Network Theory is proposed.Based on the Complex Network Theory and combined with the characteristics of urban rail transit networks,analyzing unweighted and weighted network characteristics indicators.Taking the degree,betweenness,proximity centrality,network efficiency,maximum connected subgraphs,etc.as structural characteristics indicators,taking the section capacity,station capacity,unit capacity strength,unit capacity betweenness,and capacity connection difference etc.as capacity characteristic indicators,and the positively related benefit-type indicators and the negatively related cost-type indicators are distinguished,and the network static bottleneck identification index system is established.Using the entropy weight-TOPSIS algorithm,the stations and sections are comprehensively sorted and identified according to the degree to which they are close to the static bottleneck.Taking the dynamic capacity bottleneck of the mismatch of transportation energy supply and demand under the condition of loading passenger flow demand as the object,a bottleneck identification method based on passenger flow assignment is proposed.First,carry out network dynamic passenger flow assignment: construct a service network that includes train sections edges,station access edges,and station transfer edges,fully considering the influence factors of passenger path selection,establish a travel impedance function based on volume and capacity.Based on Logit model,the Stochastic User Equilibrium passenger flow assignment model(SUE)of urban rail transit network is established,and the Method of Successive Averages(MSA)is used to figure out the flow of each edge in the service network.Then,based on the capacity load rate of edges,the identification method of the capacity bottleneck station and section is proposed.Further,the cascading failure effect is used for reference to analyze the mechanism of bottleneck formation and propagation,through the bottleneck capacity expansion and passenger flow reassignment test,take the number of bottleneck edges and the total impedance of the network as indicators,to measure the improvement degree of the network by the capacity increase of the bottleneck,so as to identify the key bottlenecks in the capacity bottleneck.Taking the dynamic service bottleneck with low service level and restricting the improvement of network overall service level as the object,a bottleneck identification method based on Percolation Theory is proposed.Apply the mature Percolation Theory in road traffic bottleneck identification to urban rail transit networks,expounding and explaining percolation process,percolation properties,etc.Based on train running speed,load factor,punctuality rate,and departure interval,establishing the comprehensive index of service bottleneck section identification.Based on traveling speed,waiting time,load factor and safety degree of the station,establishing the comprehensive index of service bottleneck station identification.Then,the comprehensive index is used as the percolation parameter,proposing the dynamic service bottleneck section identification method based on bond percolation and the dynamic service bottleneck station identification method based on site percolation.These three methods are relatively independent,and the identification object is progressive.Taking the Chengdu Metro network in different stages and different periods of time as examples,the calculation and analysis are carried out using various methods.Finally,from the three aspects of network structure,operation organization and passenger flow demand,the bottleneck elimination measures are analyzed and researched,and some practical suggestions are put forward.In terms of network structure,including reasonable consideration of network planning and improving.In terms of operation organization,including compression of departure interval,adjustment of train operation organization,and optimization of station passenger flow paths.In terms of passenger flow demand,analyzing some means to coordinate the network passenger flow demand and its distribution,such as passenger flow regulation,control and guidance.