Research On Regional Traffic Congestion Measurement And Control Based On Matching Flowing-in And Flowing-out Rates

With the acceleration of urbanization and the rapid growth of vehicle ownership,the contradiction between traffic supply and demand are prominent with each passing day,caused more and more traffic pressure to the urban road system and heavy traffic congestion in major China cities,which becomes one of the dominant factors troubled and restricted urban sustainable development.With the occurrence of Traffic congestion,the service level of traffic system would reduce,and the increasing of traffic delay and traffic accident,meanwhile,inefficiency traffic operation,due to traffic congestion,would result in energy wastage and environment pollution,which would decrease the happiness index of urban citizens.The main and difficult points to solve traffic congestion problem are accurate measurement and effective control.On the basis of existing research,this paper redefined traffic congestion,analyzed its mechanism,researched traffic measurement method and control strategy from the point of matching flowing-in and flowing-out rates of urban road section.The main contents of this paper include the following several aspects:Firstly,this paper redefined traffic congestion,analyzed its mechanism based on the flowing-in and flowing-out rates and their matching relationships of urban road section.Congestion is defined as a phenomenon that vehicles forced to go slowly,stop and go,or even stagnation due to flowing-in rate exceeds flowing-out rate in certain period time and at certain space.According to the definition,this paper studied the relationships between the change of accumulating volumes,which derived by flowing-in and flowing-out rates,and traffic congestion process,including its formation,development and evacuation.Then the traffic congestion mechanism of the basic calculating unit analyzed in this paper,as well as basic link,intersection,and networks of urban traffic system.After the practicability of traffic congestion measurement based on accumulating volumes was demonstrated,the Congestion Degree(CD)function based on accumulating volume ratio,which is a dimensionless parameter,was defined;then the traffic congestion measurement models of basic calculating unit,urban road link and intersection based on accumulate volume ratio were established respectively,made the traffic congestion measurement unified.Traffic state was divided into five levels,including free flow,reasonably free flow,light congestion,moderate congestion,and serious congestion(jam)based on the three-phase traffic theory with a.subdivision of synchronized flow and jam.In order to make the traffic state corresponding to different congestion degree,the rough set theory model was introduced to divide the interval of different CD.Simultaneously,the horizontal comparison of the CD intervals of different road grades shown that in addition to the branch road,the CD intervals of the same traffic state of the other road grades were fairly close and relatively stationary,which means compare to speed,volume and other parameters,the accumulating volume ratio have wider applicability in urban road network congestion measurement.After the CD intervals of different traffic state at different road grades settled down,the probability model based on accumulated Vehicle Kilometer Travel distribution(VKT distribution)of accumulating volume ratio was established by curve-fitting of probability distribution of accumulating volume ratio on the urban traffic networks.Then a Regional Traffic State Index(RTSI)model was proposed to evaluation the state of urban traffic networks.Then the availability and feasibility of RTSI was verified by an actual example with the comparison to TPI(Traffic Performance Index)from Urban Road Traffic Performance Evaluation Index System.Signal optimization control is one of important means to urban traffic management and control,as well as an effective method to relieve traffic congestion.As the traditional arterial coordinated control strategy is suitable for medium traffic volume conditions,its effect on arterial congestion is poor.Aimed at the traffic control and evacuation of arterials under patial congestion,this paper proposed a coordinated control strategy of green wave and red wave band,which was designed to use the green wave band for utilizing the capacity of downstream intersections and segments to discharge the congested traffic at the bottle-neck intersections rapidly,in the meantime,use the red wave band for utilizing the space on upstream intersections and segments to hold the traffic approaching the bottleneck intersections,extend the travel time to bottleneck intersections to prevent congestion spreading and feedback.Then the saturation of coordinated phase and the accumulating volume ratio of the arterial sections were chosen as evaluation indicators to measure the congestion degree of the arterial,as well as activation and termination index for proposed control strategy.Third,a relation model was adopted to explore the workable range,and at last,the computing methods of the parameters,mainly includes the period,offsets & modified time of the green wave and red wave band were put forward.With regard to the control of local congestion of urban traffic networks,on the basis of its topology and the matching relationships of the traffic flow,under the constraint of network state equations,a pinning control model for traffic network congestion based on degree correlation,which aimed at minimizing the total system cost of the vehicles running on the congested networks,was built and the corresponding algorithm and procedure were given out simultaneously.The experimental analysis indicated that different control strategy had diverse effects on urban network traffic congestion control and ordering,the mixed pinning control strategy is the optical choice.