Research On Simulating And Controlling The Generation Of Traffic Congestion In Urban Expressway

The urban expressway is the artery of the urban transportation system,which is characterized by high speed and high efficiency,whieh is mainly used for long-distance traveling.However,with the rapid economic growth and the development of urbanization process in China,the automobile procession and the resident trips grows rapidly,meanwhile,more and more travelers choose urban expressway even for short-distance travel,which result in more and more serious traffic congestion,and the urban expressway is gradually losing its functions.Although many big cities and medium-sized cities have took a series of measures to resolve these questions,these methods including road network designing,building the more efficient urban express road network,but the basic traffic facilities cannot meet with growing transportation requirements,makes the need and demand of transportation severely serious,which has caused a series of problems,such as direct economic losses and other indirect losses which includes energy waste,traffic environment pollution,traffic accidents,etc.Therefore,there is no time to delay for studying the problem of traffic congestion and reducing the traffic congestion on urban expressways.However,it is difficult to accurately analyze and simulate the process of congestion formation,congestion propagation and congestion disappearance on urban expressway based on existing researches,which leads to great blindness in the process of controlling and managing expressway traffic flow.In order to solve the traffic congestion problems of urban expressway,it is the most important basic task to study the mechanism of urban expressway congestions.In this thesis,we studied and analyzed traffic congestion propagation rules on expressway based on the web crawler technology and the improved cell transmission model,and analyzed the rules in the single ramp.In general,the major contents are summarized as follows:(1)Analyzing the characteristics of expressway traffic flow,and classifying the state of expressway traffic flow of Wanjiali Road in Changsha based on the Fundamental Diagram of Traffic Flow theory.And analyzing these factors which have an influence on traffic congestions,then established the traffic congestion evaluation index which are matching with the cell transmission model,so as to establish the base of evaluating the congestion degree.(2)Fetching the traffic data of Wanjiali Road and analyzing traffic flow with web crawlers.After analyzing urban traffic flow data of GaoDe,we found that traffic congestion of the direction from north to south is more serious than the direction from south to north in the Wanjiali Road.Therefore,we emphasized on the spatial-temporal evolution of traffic congestion from north to south directions,and analyzed the traffic congestions of working days and non-working days.(3)We sinulated and analyzed the traffic flow of Wanjiali Road in Changsha based on the improved cell transmission model,after comprehensively analyzing the data obtained from investigating,we simulated and analyzed the traffic flow from the south to the north direction in Wanjiali Road.This thesis based on the Daganzo cell transport model,introduced the cell length parameter,the convergence ratio,the diversion ratio and the off-ramp capacity parameters,and calibrated the velocity parameters,so as to make the cell transport model could more accurately study the characteristics of the traffic flow in the Wanjiali road.In addition,sensitivity analysis was made in the studies on the effect of the on-ramp traffic capacity on mainline traffic flow and the effect of the off-ramp traffic capability on the mainline traffic flow,so as to provide the theory gist for studying the forming process of urban expressway traffic congestion.(4)Based on the control principle of 'prevention first,mitigation for auxiliary' and the ALINEA closed-loop ramp control algorithm,and combined with the short-term traffic flow forecasting model,we controlled and analyzed the traffic flow of on-ramp on the expressway.At first,we select the on-ramp which connected with Renmin south road and Wanjiali road in Changsha as researching object,and we attempt to analyze the traffic flow which from south to north,and then,we analyzed the reliability of traffic spatio-temporal data,and adopted on-ramp controlling method which based on ALINEA algorithm,and finally,we simulated the traffic flow based on CTM,so as to verify the effects of the on-ramp controlling method,the results show that properly on-ramp control could effectively reducing the traffic congestion on urban expressway.