Key Intersection Group Signal Control For Traffic Overflow And Congestion Elimination

At present,the characteristics of high-intensity travel in China’s cities are becoming increasingly apparent.Affected by the urban layout and the road conditions of high-density narrow road network,there are a large number of short bottleneck sections,which are prone to long queue vehicle overflow sections during peak traffic periods,occupying the space of upstream intersections and traffic overflow congestion.Traffic overflow is highly contagious.If local congestion is not evacuated and cleared in time,it will quickly spread along the upstream intersection through the topological connection between road sections and intersections.In the road network,the failure of one or a few bottleneck intersections or sections will lead to the failure of other intersection groups through the coupling relationship between nodes,and then produce cascade effects,resulting in the paralysis of the whole traffic system and serious consequences.Therefore,it is necessary to identify the bottleneck intersection group in time,predict the overflow of the road network,regulate the road space-time resources and quickly remove the overflow congestion.Focusing on the problem of traffic overflow,identification,control and evaluation are the main processes of the paper.Firstly,according to the factors of queue length and phase sequence of upstream intersection,it is divided into mild,moderate and severe overflow according to the degree of overflow influence.The mechanism of queuing process is analyzed by traffic wave theory.It is found that there are four stages of traffic waves generated by vehicles in a signal cycle: red stop wave,green start wave,queue compression wave and secondary queue wave.The queue length calculation model is established to distinguish the overflow state of different degrees.And the overflow section and key intersection are determined.Next,the intersection group with overflow bottleneck is identified based on individual travel path.The theory of association rules is introduced to define the critical path of overflow section.Based on the traffic checkpoint data to extract the travel trajectory,the FP-growth algorithm is used to mine the frequent paths and bottleneck intersection groups of the overflow section,which shows the main source and direction of the overflow traffic flow,and defines the scope for selecting the adjustable key intersection groups.Then,different signal control schemes are adopted for different degrees of overflow.For mild overflow sections,the critical path signal optimization method based on anti overflow phase difference is adopted.Aiming at the critical path of overflow,a phase difference calculation model to prevent green light empty discharge and a phase difference calculation model to prevent queue overflow are proposed.For the traditional trunk line coordination,a series of optimization improvements are made.The concept of space-time saturation is adopted,and the traffic flow and queue length are taken as the basis of green light time allocation.Using the relative phase difference calculation model of anti overflow,it can be compatible with the left turn path,and provides a method of non-linear trunk line coordination.For moderate or severe overflow sections,the regional coordinated control method of intersection group based on the remaining queue length is adopted.In the adjustable control unit,the intersection group signal timing in the surrounding area of the overflow section shall be reasonably adjusted by compressing the green signal ratio,increasing the green signal ratio and jumping phase.Finally,the overflow simulation experiment is carried out on two cases of Zhongshan East Road in Nanjing through TESS NG micro traffic simulation software to evaluate the feasibility and effectiveness of overflow control.The optimization scheme is evaluated by the maximum queue length,maximum queue intensity,travel time,traffic volume and other indicators.Combined with the example verification,it is found that compared with the original scheme,the optimized scheme realizes the signal control response of different overflow degrees,the prevention and rapid dissipation effect of overflow,which is conducive to the balanced utilization of road space-time resources.