| As a part of urban main roads,urban express way bears heavy traffic load.With the increasing of vehicle ownership,traffic condition of urban express way has been getting worse,especially in merging area of om-ramp and main lane.Cars getting into the main lane from on-ramp will disturb vehicle flow running normally,as a result,the disturbed cars will brake inevitably and slow down and even stop to run in idle state.Thus,not only traffic congestion emerges but also emissions ascend remarkably.Less good is that toxic HC,CO and NO_X of emissions can impact residents’health and environment terribly.Therefore,the objective of this paper is to relief traffic load,improve efficiency of traffic and exert the best effectiveness of express way,and meanwhile,cut down the emission of poisonous gas.Based on researching domestic and foreign conference,this paper employs DMC in MPC to study on-ramp metering control,and research work can be summarized as follows:Firstly,an on-ramp named Taoxi in Chengdu urban elevated express way is chosen to be study object,and its road nature and traffic flow characteristic are discussed.In this section,macroscopic vehicle flow characteristic and microscopic operation condition of cars have been researched.Then the traffic dynamics model is deduced and the on-ramp traffic augmented model is developed,and these models abstract mathematics from real on-ramp system so as to provide conference for the next sections.Secondly,appropriate control strategy has been chosen and DMC theory has been researched.In this section,the transfer function is used for modelling on-ramp system and prediction model.Then the step response trial of this model is conducted and a succession of step response coefficients are captured.On-ramp traffic flow is taken as input of control system,and the traffic density of merging area is regarded as output of the system,and then the desired value of density has been chosen from traffic aspect,the desired value of density from emission is determined by the relation of emission factors and speed via MOVES,and finally the comprehensive desired value is computed by traffic combining with emission.On the foundation of discussing and fitting parameters,the control system optimization is done.Then control performance test is conducted by MATLAB to check whether the performance is the highest or not.The test result shows that the stability is so good and performance of tracking desired value is excellent even though the desired value changes.Thirdly,simulation platform is established and simulation plan is designed.In this section,field investigation data is employed to calibrate VISSIM critical parameters in order to make simulation approach real condition.Because of powerful matrix-processing and abundant simulation tools,MATLAB is applied to developing VISSIM to achieve DMC in ramp control.In order to prove the evident performance of DMC,no-metering,fixed-time control and ALINEA are added into simulation,the final result elaborates that DMC improves traffic and cuts down emission compared with fixed-time and ALINEA control. |
