Research On Macroscopic Traffic Flow Model Based On Traffic Information

The increase of traffic demand has led to serious traffic congestion problem in urban areas worldwide,and results in environmental pollution and traffic safety problems.Traffic flow theory focuses on the evolution of traffic flow,which can help alleviate traffic congestion and reduce energy consumption and emission.Intelligent transportation system(ITS)can help road users to reduce travel time through real-time information on traffic condition of the road,improve speeds,timely adjust the route,realize to drive fast and securely through guiding,thus alleviate congestion,by means of vehicle navigation system,satellite positioning system,vehicles communication systems,variable message sign and traffic radio provides.Macroscopic traffic flow model has the advantage of mathematical tractable,and is physically meaningful.Therefore,it is meaningful to model and analyze the macroscopic traffic flow models based on traffic information,for the development of traffic flow theory,and realistic traffic management,planning and control.The main work of this paper is as follows:(1)Considering the multiple density difference effect in the two-lane traffic systems,an extended lattice hydrodynamic model based on Nagatani's basic lattice traffic flow model is presented.Derive the stability condition,and the mKdV equation near the critical point of the model by linear and nonlinear analysis,respectively,as well as the corresponding kink-antikink solution which reflects density waves of the model.Results of the theoretical analysis manifest that the stable region is enlarged by multiple density difference information effect.The reason is that with considering more vehicles,more comprehensive information could be obtained for drivers to adjust speed so to increase average velocity,and reduce stop and go waves,alleviate traffic.Numerical simulation experiments based on periodical boundary validate theoretical analysis,and discover that multiple density difference effect can reduce energy consumption and traffic emissions,also it is found that three sites ahead is effective to improve traffic flow.Traffic stability,energy consumption and traffic pollutions are no longer increase obviously with further more information.(2)Propose an extended lattice hydrodynamic model in two-lane traffic systems,considering multiple information of preceding cars.Multiple density difference and multiple flux difference effects can improve traffic stability and reduce energy consumption.Stability condition is acquired by applying linear stability theory.Nonlinear analysis is conducted by reductive perturbation method,the kink-antikink soliton solution is obtained from the derived mKdV equation near the critical point.The change of the kink-antikink soliton solutions represent the fluctuation of the density waves and the stop and go waves of reality.Numerical simulations with periodical boundary are conducted to verify theoretical analysis that the more information the drivers obtain,the smoother the traffic flow becomes,and the more the energy consumptions are reduced.Even it is found that considering only one preceding car with the combination of two types of information is better to improve traffic flow as well as save energy than considering three cars ahead with single type of information.(3)Further,a unified information effect model is presented for two-lane lattice traffic flow,with comparing different effects in the various lattice hydrodynamic models.Results of linear and nonlinear analysis show that multiple density difference effect(MDDE)is the best to enlarge the stable region in two-lane systems.Followed by density difference effect(DDE),multiple flux difference effect(MFDE),and finally is flux difference effect(FDE).Numerical simulations validate theoretical analysis.In general,DDE can improve traffic condition better than MFDE.However,when density is around 0.25,MFDE can perform better to enlarge the stable region than DDE.The reason is that a small flow-rate value might correspond to either a light traffic or a heavy traffic.Results also show that the effects of these traffic information to energy consumption and traffic emissions are consistent with that of traffic stability.(4)A two routes traffic network consisting of a diverge and a merge,with fixed upstream demand and a bottleneck in the merge point is discussed.Dynamic vehicles that consider real time traffic information are introduced to the system.Cell transmission model(CTM)are adopted to simulate and analyze the dynamic evolution process and the finally states of the system.With the participation of dynamic vehicles,three new states emerge:route switching state with congestion,while congested queues nearly reach the diverge point;periodical path switching state with both links can reach free flow,periodical path switching state with only the smaller capacity link can reach free flow state.Simulation results show that traffic states are affected by the proportion of dynamic vehicles,network structure and fixed diversion ratio of static vehicles in the two routes,so the results are benefit to network design and ITS management and control.(5)Aim to the two routes traffic network in the above section,macroscopic dynamic evolution process of the network is analyzed by macroscopic network kinematic wave model,with queues spillback in the diverge and merge,and the propagating of shock waves.When the ratio of capacities of the two intermediate links,the ratio of static vehicles which select fixed routes,and the ratio of dynamic vehicles that consider real time traffic information are determined,analytical solutions of the system are derived.Analysis results indicate that three new states emerge in the system with the induction of dynamic vehicles,which is same as the simulation results in the above section.Also a new damped oscillation state is emerged.Periods of the two periodical path switching states and analysis formulas of the boundaries of all the regions are derived.Nonexistence of periodical path switching state with only larger capacity link can reach free flow is also explained.As well as the relationship of the states of the system and the proportion of dynamic vehicles,network structure and fixed diversion ratio of static vehicles in the two routes are derived.Simulation experiments verify analysis results.And the results are benefit to road network design and traffic management and control.