The Study Of A Cellular Automaton Model For Mixing Traffic In A Roundabout

In recent years, the traffic congestion problems have become worse due to the percentage of various motor and non-motor car holders being snowballing. Meanwhile, a lot of here and overseas scholars have to focus on the traffic flow models in the study. Among the traffic flow models, cellular automaton model can be widely used for its convenient operation and easy to computer implementation. In real life, roundabout is the same as the other types of intersections. For instance, it also has many bottlenecks which can lead to frequent traffic accidents and traffic congestion phenomenon. Besides, it has been difficult to solve the traffic congestion because of the complex traffic behavior which occurred on a roundabout.This thesis first introduced the research process of the traffic flow model, and over-viewed several classical models in the macroscopic model, meso-scopic model and microscopic model of the traffic flow models briefly. Besides, the thesis also introduced the concept and relationship of the main parameters in the traffic flow model, and the boundary conditions of cellular automaton model. What’s more, the thesis put emphases on the cellular automaton model of microscopic model. Furthermore, based on the existing research on the cellular automaton model, two cellular automaton traffic flow models for mixing traffic in a single-lane roundabout and two-lane roundabout are proposed, and the characters of traffic flow in these models are presented and analyzed. The detailed findings are shown as follows:1) There are many classical cellular automaton models have been reviewed, including Wolfram’s model No.184, NaSch model, FI model, NaSch’s improved model and FI’s improved model about single lane, symmetric two-lane cellular automaton model about two lanes and multiple lanes model based on NaSch model about multiple lanes. Besides, these models have been analyzed comparatively, for the following study lays a theoretical foundation.2) With respect to the two-maximum-speed vehicles mixed in realistic life, based on the NaSch model, a cellular automation model is proposed to describe the mixing traffic flow in a single-lane roundabout. Under the condition of open boundary, the simulation results indicate that the relationship between the injection probability and the system density, velocity, flow for different mixed proportion coefficients. What’s more, when the injection probability is near the critical value or greater than the critical value, the space-time diagrams about one-maximum-speed vehicles model and two-maximum-speed mixed vehicles model in the system are constructed. Furthermore, the phenomenons of vehicles’go-and-stop occurred on the injection-roundabout-lane in this two models are compared and discussed.3) Considering the actual road’s structure about two-lane roundabout, a cellular automaton model is introduced to describe the mixing traffic flow in a roundabout with the inner-roundabout-lane, outer-roundabout-lane, injection-roundabout-lane and extraction-roundabout-lane. In this model, the lane-changing behaviors of vehicles on the injection-roundabout-lane and extraction-roundabout-lane are taken into account. Under the condition of open boundary, the simulation results show that the relationships among the system flow, average velocity and the injection probability, extraction probability, braking probability are investigated in detail, and the system phase diagram is constructed and discussed based on the change law of flow in the system.