| At present,the freeway of China is in the phase of the transition of large-sacle construction to scientific management,and the control of traffic congestion has become an important part of freeway operation management.Ramp control,as one of the significant control methods of active traffic management,has received extensive attention from all over the world.The research on the basic theory of ramp control has certain theoretical significance and can be a reference for the scientific formulation of the strategy.However,the accuracy of the data which is used in the existing research on traffic flow characterics analysis and simulation evaluation of the freeway is not enough.In fact,with the development of traffic detection technology and computer technology,the acquisition of high-precision real-time traffic flow data has become possible,which lays the foundation for the development of freeway real-time traffic control technology.The traffic control strategy represented by the ramp control has been more and more put into practical application to solve the traffic congestion on freeway.Therefore,based on the PeMS system(Performance Measurement System),this paper takes the South Bay Freeway(SR-237)in California as the research object,studies the traffic flow characteristics of the freeway,and puts forward the congestion control strategy for its characteristics for the purpose of providing a reference for the decision-making of traffic management department.At the same time,by summarizing the research and application of domestic and foreign scholars in the field of freeway management and control strategy,this paper carries out research from the following three areas:the selection of highway data acquisition sites and data characteristics analysis;the control strategy of freeway under the congested scene;the effectiveness of ramp control strategy and evaluation of control effect.The main research contents are as follows:(1)Firstly,the data collection and data characteristics of the freeway are analysed in detail.The selection and data processing methods of data mining are analyzed.On this basis,the traffic flow characteristics of the selected sections are studied from the perspectives of occupancy rate,average speed,traffic volume and vehicle composition.Finally,the congestion status of the South Bay Freeway(SR-237)is briefly described.(2)Taking the freeway under congested conditions into account,this paper proposes the control strategy.This chapter discussed the current control strategy which is commonly applied:mainline control,route guidance and ramp control.The main contents and technical characteristics are analysed respectively.According to the road conditions selected in this paper,the ramp control strategy is selected.Then,the paper discusses some signal control strategies and various classical algorithms in ramp control,and briefly describes the respective advantages and disadvantages.Finally,the isocyclic release strategy and ALINEA algorithm are selected.Afterwords,the indicators of control effectiveness based on the total travel time(TTT),total waiting time on the ramp(TWT)and total travel distance(TTD)are established.(3)Validity of ramp control strategy and evaluation of control effect.First of all,the corresponding simulation experiment scene is designed.Secondly,based on the traffic data obtained from the acquisition and processing,and the calibrated parameters,the simulation of each scene is realized through Vissim’s COM interface.The traffic conditions before and after the implementation of the measures will be compared with the selected evaluation indexes.The results show that the ALINEA control algorithm can effectively improve the congestion of the selected freeway.In this paper,data acquisition and processing,formulation of strategies and modeling analysis are adopted to study the control strategy for the freeway under the congested condition.And provide relevant decision support and theoretical basis of the management of freeway. |
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