| Roundabout has been widely used in urban areas worldwide because of their advantages of simple organization and fewer conflicts at the free flow state.However,with the increasing traffic pressure,when a roundabout tends to saturate,each traffic flow would obtain the right of way simultaneously,which results in the traffic flows’ conflict and blocks the roundabout from obtaining maximum efficiency/capacity.Therefore,signal control can be introduced to address this issue and further improve roundabout efficiency.Although fixed-time signal control is a common signal control approach,it is only suitable for intersections with stable traffic.The actuated signal control can adjust the green time of each phase according to the arrival of vehicles in the approach carriageway,but most of the actuated signal control uses a fixed phase scheme,the phase scheme cannot meet the actual traffic demand,resulting in more and more roundabouts become bottleneck areas of urban road.For effectively relieve the problem of insufficient traffic capacity at multi-leg roundabouts,this thesis focuses on phase design and actuated signal control to better meet the real-time traffic demand,improve the utilization of roundabouts’ spatial and temporal resources,and provide new ideas for expanding to the actuated control of green wave control and even the whole road network.In the case of uneven spatial distribution of traffic flow at multi-leg roundabouts,for the problem of complex phase setting,this thesis proposes a combined phase design model based on the traffic flow characteristics and capacity in each area.And by analyzing the timing parameters of actuated signal control,this thesis optimizes its timing and process based on the combined phase design model.The main research of this thesisis as follows:(1)Analysis of traffic flow characteristics and capacity for multi-leg roundabouts.Firstly,this thesis studies the composition structure of the roundabout and divides the roundabout into different areas.Then the traffic flow operation characteristics are analyzed for each area.Finally,the actual capacity is calculated according to the traffic flow operation characteristics,which lays the foundation for the subsequent combined phase design model of multi-leg roundabouts.(2)Establishment and solution of the combined phase design model for the multi-leg roundabout.This thesis analyzes the principles and priorities of phase design and converts the phase and the phase scheme into mathematical expression.Considering the geometric characteristics of the multi-leg roundabout,the combined phase design model is established with the constraints of the phase design principle and the capacity of the bottleneck area,then this thesis uses Python programming language to solve this model.The optimal phase phase scheme is set according to the actual traffic demand of the roundabout,which improves the utilization of spatial and temporal resources at multi-leg roundabouts and provides ideas for the subsequent actuated signal control research.(3)Optimization of actuated signal control based on combined phase design model.First,the historical traffic state parameters are collected in real-time by the detectors in the circulating lane and each carriageway.Then this thesis uses a Long Short Term Memory neural network(LSTM)to predict the data of the next cycle and input its data into the combined phase design model of multi-leg roundabout to obtain the optimal phase scheme.Secondly,this thesis applies the appropriate overlap phase methods to different phase schemes and sets reasonable actuated signal timing parameters,and develops an actuated signal control optimization process,so the phase scheme can be adjusted with actual traffic flow in the actuated signal control.(4)Case study.Taking the roundabout of Houcheng Street/Beishan Road in Jinhua city as an example,this thesis investigates the traffic volume,signal timing and and bottleneck areas with saturated headway,density and speed.Using the Vissim simulation software and selecting three evaluation indicators of queue length,number of stops and delays,the combined phase design model is verified by comparing the status quo phase scheme with the combined phase scheme.Then,by comparing before and after the optimization of actuated signal control within two periods of morning and evening peaks,the feasibility of the actuated signal control method based on the combined phase design model is verified.The results indicate that the proposed combined phase design model can improve the applicability of actuated signal control. |
