Study On Bottlenecks Identification And Coordinatied Ramp Control In Urban Elevation Expressway

As an urban backbone road network,the elevated expressway has played an important role in diversion of cross-boundary traffic,contact center city and delegation in the early days.However,with its capacity no longer able to meet traffic demand,traffic congestion on the elevated expressway is increasingly apparent.Due to the structural problems of elevated expressways and the constant changes of traffic volume,there are many dynamic or static traffic bottlenecks in the road network.These bottlenecks are the important root causes of traffic jams on the elevated expressways.Therefore,how to identify these bottlenecks and develop scientific traffic control measures are prerequisites for managing congestion on elevated expressways.This paper studies the identification,time and space scope and impact of bottlenecks,and discusses the traffic congestion caused by the bottleneck mitigation from the perspective of ramp control.The specific research content mainly has the following aspects:(1)Taking Chengdu No.2 Ring elevated expressway as the research object,the characteristics of traffic flow were studied.The traffic flow characteristics of two types of confluence zones with direct acceleration lanes and parallel acceleration lanes are analyzed respectively,including the time-varying characteristics of traffic flow during rush hour,the distribution of velocity,density,and headway.At the same time,the traffic flow characteristics of the basic sections are studied,including the time-varying characteristics of the three parameters of the traffic flow in the rush hour,the speed-density relationship and the flowdensity relationship.(2)the paper reviews and summarizes the main traffic bottleneck identification algorithms.In view of the defects that the bottleneck location can not be accurately identified,this paper proposes a bottleneck identification algorithm based on the different scale detection data.Large-scale detection data can only locate the bottleneck to the detection coil position,small-scale detection data has strong volatility,and is easy to form the shortcomings of misjudgment.Fimally,an example is given to proves the effectiveness of the algorithm.(3)Aiming at the multi-bottleneck of elevated expressway,local ramp metering strategies and coordinated ramp control strategies are studied.Based on the existing research,local ramp metering in the multi-bottleneck considers the limitation of the queue length of the urban elevated expressway.Based on the heuristic control method Bottleneck,coordinated ramp control in the multi-bottleneck is studied with flow and occupancy as control variables respectively.Finally,taking Chengdu No.2 Ring Expressway as an example,the actual survey data is taken as input to establish and calibrate the Vissim simulation model.Six simulation scenarios were designed respectively.The Vissim COM interface was used to control the scenes,and the control effects of different scenes were analyzed and compared.The validity of local ramp metering and coordinated ramp control in the multi-bottleneck was verified.