Research On The Optimal Control Of Urban Traffic Signal Under Oversaturated Traffic Conditions

With the increasing number of motor vehicles and the expansion of urban road network,urban traffic congestion is becoming increasingly serious.Oversaturated traffic conditions are the main factor of city road network congestion.The intelligent signal control technology becomes a hot research topic in the area of oversaturated traffic conditions in urban traffic.Various control theories and methods are proposed,and good results are obtained in practical application.However,the urban traffic flow is more complex and changeable under oversaturated traffic conditions,and there are many difficulties in signal control.Therefore,the research on the optimal control of urban traffic signal under oversaturated traffic conditions is of great importance for theoretical significance and application value.The division of control subareas and signal optimization method are researched under oversaturated traffic conditions.Fuzzy control algorithm is used to calculate the correlation degree between intersections according to the complexity of traffic flow under oversaturated traffic conditions,and the division method of control subareas is proposed.Then,the definition method of transition zone,blocking zone and dissipation zone is designed,and signal control optimization method for the above three zones is proposed.Finally,simulation results show the feasibility of the proposed method.Main works and achievements of this paper are listed as follows:(1)Basic theory of traffic flow is introduced and the characteristics of traffic flow at signalized intersections under oversaturated conditions are analyzed.The mechanism of the traffic congestion and the diffusion process of congestion from single intersection to region are summarized.(2)The dynamic division method of subareas under oversaturated traffic conditions is designed.Firstly,the identification method of oversaturated conditions is putted forward according to the saturation of intersection and the queuing condition.Then,the fuzzy control algorithm is used to calculate the correlation degree based on the vehicle capacity ratio and the influence degree of traffic demand.Finally,the division method of subareas is proposed based on the congestion level of intersection and correlation degree between intersections.The designed method can be used to classify the different subareas.(3)The optimal control algorithm is researched under oversaturated traffic conditions.The control range is extended into three control region,which are transition zone,blocking zone and dissipation zone,and different control schemes are proposed according to the control requirements of these three regions.The coordinated control algorithm of green wave based on the balanced queue length is designed for the transition zone,the coordinated control algorithm of red wave based on the maximized queue length is designed for the blocking zone,and the coordinated control algorithm of green wave based on the minimum queue length is designed for the dissipation zone.The calculation of initial control parameters and dynamic optimization are studied in the design process of these algorithms.(4)A road network model is established based on the partial traffic area of Shaoxing city by using traffic simulation software.Partial traffic flow on morning peak in the working days is used as experimental data to complete simulation.Finally,the experimental results show the effectiveness of the proposed division method of subareas and signal optimization control algorithm under oversaturated traffic conditions.