Studies On Traffic Accidents In Traffic Flow Cellular Automaton Models

With the development of the city economy, the contradiction between the growth of traffic flux and the road condition is becoming prominent, which has greatly restricted the development of city economy. Therefore, in recent years, many experts in different countries have taken traffic problems seriously and proposed many models of traffic flow. Among these models, cellular automaton model allows the flexibility to adapt complicated features observed in real traffic and can be used very efficiently for computers to perform real-time simulations. Cellular automaton provides an available model tool for researching on system global behavior and complex nonlinear dynamical phenomena of traffic flow dynamics theory, so it has been concerned extensively.This dissertation consists of the following three main parts:(1) We study analytically the NS (Nagel-Schreckenberg) traffic flow cellular automaton model. A set of equations about the density of the vehicles is put forward and the relation of average velocity and traffic flow to the car density with various stochastic braking probabilities are obtained. The exact mean field equation of the car accident probability is obtained based on the conditions for the occurrence of car accidents. Furthermore the steady states of car accident are investigated in deterministic NS model. The Spatial-temporal diagrams are described in various steady states and the relation of car accident and the initialization is obtained.(2) Based on VDR (Velocity Dependent Randomization) traffic flow model, a mixed traffic flow model accord with the fact is given to investigate the characters of the mixed traffic flow with different maximum velocity. The proportion of the slow car, the stochastic braking probability and the limited velocity are analyzed. Theoretical analyses give an agreement with the simulation results.(3) There is disfigurement in the highway commonly, so a modified cellular automaton model is devised to study the effect of the especial section of the highway on the traffic flow. The simulation shows that the especial section of the highway can result in phase separation. A saturated traffic flow exists in the basic figure and various characters of the car accidents in every section of the highway are indicated. After analytical study, some exact results about the critical density and the occurrence of car accidents are obtained. The results can not only provide some beneficial guidance for the management in the highway but also have some physics meaning.