Signal Control And Simulation Of Four-Branch Roundabouts

Traditional roundabout has certain self-regulation ability under the condition of small traffic volume.However,the priority right of access for ring-wound vehicles and ring-wound vehicles is not clear.With the rapid increase of car ownership in cities in China,the conflict flow between vehicles in the ring road without signal control and vehicles entering the ring road arrives at the interleaving point at the same time,which makes it impossible to get out of the ring road in time.It leads to the increase of intersection delay,queue length,congestion and lock-up.In this context,how to transform the roundabouts has become an important issue.Most domestic scholars usually adopt the following three solutions:? remove the original ring island and change it to a normal intersection controlled by signal lights;?widen the entrance and exit,use left-turn,right-turn,direct lane;? use signal control.This paper discusses the applicability of several control modes of circular intersection by means of signal control and VISSIM simulation software of road traffic,taking the actual data of Dalian Shuma Square as an example.Firstly,this paper briefly introduces the basic concepts of roundabouts,and expounds the development history,definition and composition of roundabouts,as well as the classification of roundabouts.Secondly,three control modes:priority control,each phase for entrance control and two-step left control,as well as timing model,are introduced.A new two-step left control method,Sazi timing model,is proposed.The phase of the control method is adjusted,and then the superposition optimization is carried out.Then,several control modes are calculated by using the flow data of field investigation,and the model selection and modeling are carried out by using VISSIM software.Finally,this paper designs a large number of simulation experiment schemes,and confirms the superposition optimization by analyzing the simulation experiment data,confirms that the average delay increases with the increase of left-turn traffic flow,and draws the following important conclusions:(1)When the total flow is less than 4200veh/h,the priority control is the best.When the total flow is between 4200 and 5500veh/h,the each phase for entrance control is the best.When the flow is more than 5500veh/h,the two-step left control is the best.(2)By comparing the two-step left Yang Xiaoguang's control model with the new model,it is found that the left-turn flow adaptability of the two models is different under different left-turn lanes,and the advantages and disadvantages of the two models under different conditions are obtained.(3)Questioning the basis of left-turn lane division of HCM2000,it is concluded that the threshold of left-turn lane number of Yang Timing Model is between 379-400veh/h and that of Sazi Timing Model is between 408-448veh/h.In this paper,a new two-step left control model for roundabouts is proposed,which provides a theoretical basis for the division of left-turn lanes at roundabouts and provides a reference for the selection of control models at roundabouts.