Study On The Identification Of Bottlenecks In Urban Road Network And Its Application

Congestion has become a common traffic phenomenon,it not just occur on individual road section or node,but rather on the road network.Congestion is usual caused by the existence of traffic bottlenecks in the network.Therefore,the essence of alleviating or even solving congestion problem is to solve the traffic bottleneck.So,it is of great practical significance to study the characteristics and identification methods of traffic bottlenecks.This paper focuses on the bottleneck identification in regional networks of city.This article is divided into three parts: fixed road bottleneck identification,fixed node bottleneck identification and dynamic bottleneck identification.Firstly,the concept of traffic bottleneck is expounded,and the causes and characteristics of bottlenecks in urban road network are analyzed.The traffic flow characteristics at the bottleneck of the road section are analyzed by using the relationship between the two parameters in traffic volume,vehicle speed and density in macro traffic flow theory.Considering the "first-in and first-out" condition and the equation of traffic flow at the up and down intersection,the traffic flow characteristics at the intersection bottleneck are presented simply and clearly by using graphic method.Secondly,based on the idea of service level,taking fully into account the influence factors of vehicle influence coefficient,lanes width reduction coefficient,lanes number correction coefficient and influence coefficient of intersection,the traditional saturation calculation method is used to determine the service level corresponding to saturation,so as to determine the road bottleneck in network.When the service level is D,and the saturation is not less than 0.9,then the road will be regarded as bottleneck section.Then,based on the thought of service level,this paper identifies fixed bottleneck intersections by proposing a fuzzy comprehensive service level method,this method takes the saturation as the main evaluation index and the satisfaction of the passengers through the intersection as the auxiliary evaluation index.The weight idea,establishing weight set and fuzzy mathematics principle are applied to get fuzzy comprehensive evaluation set.Finally,according to the principle of maximum membership degree,determining the service level of intersection and referring to the correspondence between comprehensive service level and saturation,identifying fixed bottleneck intersection.When the service level of intersection is D,and the saturation is gteater than1.0,it will be regarded as bottleneck intersection.Finally,considering the red waiting time at the intersection,this paper analyzes the distributed-wave of the vehicles waiting in line before the intersection,improves on the traditional resistance function,and constructs the dynamic impedance model equation which can describe the congestion in the road in real time.Traffic simulation software is used to carry out the simulation analysis and the model results are evaluated.Based on the construction of the dynamic impedance function model,the abstract regional road network topology is constructed.The random user dynamic optimal traffic assignment model is adopted to transform the traffic demand and carry out the dynamic traffic assignment.Take the regional road network of Zhongshan West Road,Fuhe Road,Yanjiang Avenue and Hongcheng Road as an example to analyze the evolution process of road network bottleneck and draw the relationship between the bottleneck status of network,bottleneck distribution,bottleneck scale and traffic demand.Identify the chain bottleneck in the road network and take it as the research objective,identify the primary bottleneck of the chain bottleneck,and provide a strong theoretical basis and positive target for traffic managers to alleviate the congestion.