Research On Coordinated Control Method For Urban Intersections Under The Oversaturated State

With the development of society and the improvement of people’s living standards,the motor vehicles population is increasing.However,there is a contradiction between limited road space resources and increasing traffic demand,which leads to the phenomenon of vehicle congestion at the intersections in the road network.The traffic flow with high saturation brings a great burden to the traffic system.To this end,how to obtain an effective and smooth transportation system under oversaturation condition has become the focus of many experts and scholars.Considering the passive signal control and active traffic assignment,this paper proposes a signal timing scheme of an isolated intersection,a discrete control model for urban arterial road and a stochastic user equilibrium assignment model to study the control problem of traffic flow in road network.The simulation results show that the traffic efficiency and traffic conditions are improved.The main work is as follows:In this paper,a two-step fuzzy logic controller is designed for signal timing of a single intersection.the signal phase is determined first,and then the green time delay is determined.Because the fuzzy decision of signal phase will lead to the unordered phase problem,an artificial phase sequence rule is introduced,combining with fuzzy logic to determine the phase together to ensure that the main signal phase can be executed sequentially.The traditional fuzzy controller often uses the current traffic flow as the reference input.This paper predicts the traffic flow through the wavelet neural network and uses the predicted flow as the controller input,so that the signal control can indirectly reduce the influence of the future vehicle arrival rate.Considering the time-varying characteristic of traffic flow,a timevarying membership function is designed to adapt the traffic flow.Due to the difficulty in determining the parameters of the fuzzy controller,a differential evolution algorithm is introduced to optimize the fuzzy rules to avoid artificially determine the control parameters.Compared with traditional fuzzy controllers and timed control,the control method of this paper can significantly reduce the average vehicle delay at single intersection.Aiming at the signal control problem of the arterial intersection,this paper proposes a control model based on discrete traffic flow.The Robertson discrete formula is used to describe the discrete relationship between the upstream and downstream flow.It is proved that the downstream vehicle arrival rate satisfies the cyclical relationship when the turning traffic flow is less.On this basis,using the periodic array to save the intermediate variables in the model,the traffic parameters of the upstream and downstream can be calculated by the look-up table method instead of the recursion method,which significantly reduces the computation time.When a traffic accident at a certain intersection causes the traffic flow to be supersaturated,the traffic capacity is estimated by the improved cellular automaton model,and then the queuing factor is designed to manage the queuing vehicles at the intersection of the arterial road.Through the given objective function,the genetic algorithm is introduced to optimize the offset and green time of each intersection.This paper presents a dynamic traffic assignment algorithm with flow control to actively manage traffic demand.On the path probability selection model,the link repetition degree coefficient is added to avoid IIA features.Since it is very time consuming to calculate all paths between OD points,the kshortest path algorithm is used to select the path set.According to this path probability model,an equivalent mathematical model is designed and the path flow solution is proved to be unique.For the links with high assigned traffic flow,the SOM neural network is used to cluster the links with high correlation with them.Then these links are applied a penalty factor and path number between OD points is increased to reassign traffic flow.The simulation shows that the traffic flow in the road network can reach the new stochastic user equilibrium state and that of the high flow links can be evacuated to other links.In this paper,the traffic flow is controlled by signal timing and traffic assignment.The simulation results show that the control strategies can effectively reduce the queue vehicles and vehicle delay.