Research On Traffic Flow Modeling And Simulating Based On The Lattice Hydrodynamic Model

Traffic flow operation state directly influences the stability of the city traffic system. City traffic system instability will bring to social environment with various unfavorable factors, such as traffic congestion, environmental pollution, waste of resources, frequent accidents, etc.. The property of traffic flow is investigated based on the lattice hydrodynamic model in closed system and open system, respectively. The research unfolds from two subjects. On the one hand, with the help of the intelligent transportation system (ITS), one-lane lattice hydrodynamic model and two-lane hydrodynamic model are constructed in a closed system respectively. These models are analyzed by the linear and nonlinear analysis, and numerical simulation is carried out to verify the theoretical analysis results. In addition, evolution of different disturbances in metastable region is investigated. On the other hand, in open system, the new two-lane model is applied to different traffic bottleneck and the empirical congested traffic patterns are reproduced. The evolution mechanism and formation condition of different congested patterns are analyzed. The contents of this dissertation are as follows:(1) Considering the effect of multiple density difference in closed system by means of ITS, the density difference cooperative lattice hydrodynamic model is proposed. Stability of the new model is obtained by using linear stability. The nonlinear analysis is also conducted by using a reductive perturbation method. The modified KdV equation is derived and the corresponding kink-antikink solution is obtained. Numerical simulations show that the stability of the cooperative driving model can improve the stability of traffic flow. Furthermore, the two-lane lattice hydrodynamic model is established based on the single lane density difference model. The theoretical analysis and simulation study are also carried on the two-lane model. Analysis results suggested that density difference effect in two-lane lattice model can improve the stability of traffic flow.(2) According to the synchronous flow characteristics described in Kerner’s three phase traffic flow theory, density cannot fully reflect the current traffic flow state. Hence, we establish cooperative driving model by considering the effect of multiple flux difference downstream. Through the theoretical analysis, the analytical linear stability condition is obtained. The mKdV equation is inferred from the new model and the analytic solution is derived. According to the results of the analysis of linear and nonlinear theory, phase diagram on sensitive coefficient and density is presented to illustrate the stability effect of flow difference information on traffic flow. Furthermore, optimal scope of cooperative driving in the ITS system is also presented through the numerical simulation.In addition, the two-lane lattice hydrodynamic model is presented by introducing the flux difference effect. The evolution of different perturbation over time in metastable region is investigated by numerical simulation in detail besides the linear and nonlinear analysis of the new model.(3) Based on the two-lane density difference model established above, firstly, the KdV equation is derived in closed system. Then, the accurate soliton solution is obtained by using the inverse scattering transform. Secondly, the soliton which can keep shape and propagate upstream emerges during the numerical simulation in closed system. In addition, the density of the last lattice located exit fluctuates with random perturbation mode in open system. By adjusting the system of initial density and the amplitude of perturbation, various congested traffic pattern, such as moving localized clusters (MLC), stop-and-go waves (SGW), oscillating congested traffic (OCT), homogeneous congested traffic (HCT), are presented in phase diagram. In addition, the sptio-temporal diagram of all the congested traffic patterns showed in phase diagram are presented through the numerical simulation.(4) In order to overcome the phenomenon of vehicle moving back in existing model, the improved two-lane lattice hydrodynamic model is constructed by revising the flow transfer function. Unlike the previous two-lane model, the conservation equations of the left lane and right lane are independent while correlated with new flux transfer function. First of all, this dissertation designs three type on-ramps, namely, one deterministic on-ramp and two stochastic on-ramps. Applying the new model to stochastic on-ramp, all the congested traffic states, such as HST, MLC, PLC, SGW, OCT and HCT, can be produced by numerical simulation. Secondly, the combination bottleneck of on-ramp and off-ramp is designed to investigate the traffic behavior under open system. Using numerical simulation find that all the congested traffic states observed in empirical traffic can emerge in the combination bottleneck. Furthermore, under the same initial condition, the congested degree of traffic flow in combined ramps is far less than the degree of on ramp bottleneck.