Research On Optimization Of On-ramp Metering In Urban Elevation Expressway Based On ALINEA

The elevated expressway in China presents a form of elevated expressway and ground expressway.It can improve the traffic conditions during initial operation period.However,with the increasing of operating time,the frequent and occasional congestions of elevated expressway is becoming more and more serious under the influence of the vehicle's growthexternal,etc.Ramp metering is one of the traffic control methods that can effectively alleviate the congestion of urban expressways.So it is important to reduce the confluence conflict and improve the running status of mainline by researching and applying the ramp metering strategy.Based on a large number of references to ALINEA,this paper summarized the defects and possible improvement direction in the application of ALINEA.And the ALINEA extension algorithms were divided into three types:fixed parameter type,parameter adjustment type and coordination control type.Then,adopting the traffic flow model parameter measurement method of expressway traffic data,the traffic flow characteristics of Chengdu 2nd Ring Elevated Road were investigated.In view of the video material,this paper extracted "speed-time headway" data and analyzed the difference between the traffic flow characteristics of inner lane and outer lane.Due to the difference of traffic flow characteristic analysis,the optimization of ramp metering was considered.And the simplified model of expressway traffic flow with multi-lane was developed in this paper.Based on the model simplification hypothesis,this paper deduced the density dynamic equation and queuing length dynamic equation of urban expressway.The dynamic equation was used for inferring the density differential equation and the queuing length differential equation.In order to avoid the idea that the inner lane and outer lane in the original ALINEA were equal during the process of determining the ramp metering rate,the ML-ALINEA and the real-time estimation algorithm of the metering rate reduction factor was proposed by the multi-lane optimization of the original ALINEA algorithm.In the development of ramp metering strategy objectives,reducing the density of on-ramp and highlighting the difference of traffic flow characteristics between lanes were taken into account.The error function and the closed loop was developed corresponding to dynamic equation and differential equation.Then,a multi-lane ramp metering algorithm established on density dynamic equation and density differential equation was proposed.Finally,in order to test the optimization of ramp metering strategy proposed in this paper,the corresponding simulation experiment scenario was designed.The simulation of each scenario was implemented via the parameter calibration,Vissim VAP and COM interface.The control performance of each scenario was compared with the evaluation index,and the effectiveness of the proposed ramp metering strategy was verified.The improved effect of optimized ramp metering strategy is superior to original ALINEA.