Study On Traffic Flow Based On Cellular Automata Theory

As the national economics rapid developing and cities scale becoming larger and larger, it has became more and more serious that the problems of urban transportation block. How to improve the traffic state is a issue that must be dealed with, the studies and the nature of traffic flow can help solve it. The exponential rate of increase in freeway traffic is expanding the need for accurate and realistic methods to model and predict traffic flow. Traffic modeling and simulation facilitates an examination of both microscopic and macroscopic views of traffic flows and is therefore considered one of the most important analytical tools in traffic engineering.This paper presents some cellular automata models for traffic flow simulation. Firstly, the celluar automata theory was introduced, cellular autoata models quantize complex behavior into simple individual components. In general, CA are idealization of physical systems in which both space and time are assumed to be discrete and each of the interacting units can have only a finite number of discrete states. Based on the cellular automata theory, this paper describes the moving character of vehicles as changing rules of cellular automata, thus traffic flow simulation models based on cellular automata are presented. After calibrating the basic parameters such as cellular length, maximum speed and so on, the traffic behaviors such as free moving, following, decelerating are described by the special changing rules of cellular automata. All the rules are also explained in great detail including a minimal model of NaSch and FI which reproduce the basic features of real traffic. An improved one-dimensional CA traffic model was proposed to describe the freeway traffic under the periodic boundary conditions. This model was based on the NaSch model, it can describe stop-and-go traffic, which gives a better description of the phenomena observed on highways with a slow-to-start rule. It is found that there exists the metastability and hysteresis effect of traffic flow in the neighborhood of critical density under different initial conditions. A computer simulation system named CATS was fulfilled with all celluar automata models in JAVA language. It proved some of these phenomena, observed in vehicular traffic under differentcircumstances, include transitions from one dynamical phase to another, criticality and self-organized criticality, metastability and hysteresis, phase-segregation, etc. Anslytical as well as numerical techniques of statistical physics are being used to study these models to understand rich variety of physical phenomena exhibited by vehicular traffic. Mean field theory is proposed for analysis the relation of traffic flow density and speed. In the last, traffic jams in the congested traffic flow are investigated by the computer simulation and the analytical method, this paper looks at this question in particular from the perspective of breakdown behavior, i.e. the transtion from free, "laminar" traffic to congested traffic. The typical traffic jam instability is intuitively explained via the insight that stable jams exist once time headways at jam outflow are larger than time headway in dense traffic. In addition, the feasibility and rationality to apply self-organization theory on traffic flow study are discussed, fractality and dissipation in traffic flow are studied preliminary.In a word, the studies of this paper have a profound function to traffic control and management.