Uninterrupted Traffic Flow Modeling With Cellular Automata Model

Traffic flow theory mainly studies the changing dynamics in time and space dimension.Only to understand the basic characteristics of traffic flow parameters and the relationship between them,exploring the mechanism of traffic congestion,can we propose effective preventive measures and solutions to alleviate traffic congestion,environmental pollution and traffic accidents and other traffic problems.Traffic is a complex system,and traffic flow modeling can reproduce and explain many complex traffic phenomena.Cellular automata(CA)model was used as a tool to model continuous traffic flow,such as highway and urban expressway.Previous CA models had insufficient consideration of weather factors,on the basis of the existing researches,the classical CA model is improved to study the traffic flow characteristics and change rules under different parameters,more actual road conditions were considered.The specific works and results are as follows:Road adhesion coefficient was used to quantify weather factors,and dynamic safe gap was derived.It was introduced into the deterministic deceleration step of NaSch model,and a single-lane model(SNF model)that was safer and more consistent with the actual road environment was established.By comparing the fundamental diagrams and density-velocity curve of SNF model and two classical models in normal weather,it is found that SNF model has the highest flow rate in the density interval[0.16,0.5].SNF model takes the front car effect into account,thus higher average speed and less deterministic kinetic energy loss.Then,the SNF model was used for numerical simulation under different weather conditions to analyze the variation rules of traffic flow and kinetic energy loss under different speed limit strategies.The results show that the speed limit on rainy days will reduce the flow rate and increase the total kinetic energy loss at most densities in[0.2,0.5].Speed limit in snowy day can reduce road flow and increase kinetic energy loss obviously.The consequence of speed limit is similar to the changes of flow rate and kinetic energy loss with density when the road surface is icy.Road adhesion factor and visibility factor were introduced to modify SNF model,and the improved SNF model was extended in two-dimensional.According to the degree of radicalization,drivers are divided into three types,namely,aggressive type,neutral type and conservative type.Random slowing probability and lane changing probability are taken as two quantitative attributes of different drivers.Simulation results show that the presence of aggressive drivers can significantly improve the road flow and capacity in the middle density range.The influence of neutral drivers on the traffic flow is small,but with the increase of the proportion of conservative drivers,the traffic flow of the road system decreases obviously.Positive lane change only contributes greatly to the speed increase in a certain density range.Considering that the vehicle is equipped with an adaptive cruise control(ACC)system and the vehicle is driven manually,a hybrid traffic flow CA model is established.Simulation results show that the increasing of ACC vehicle permeability and the speed expectation factor of ACC vehicle driver will greatly improve the traffic capacity,the kinetic energy loss will be better controlled,which has a positive effect on improving the current road traffic.Based on NaSch and NF model and consideration of road adhesion coefficient,SNF model was established to analyze the influence of speed control strategy on traffic flow and kinetic energy loss under different weather conditions.Furthermore,the random slowing probability and lane changing probability are used to distinguish three types of drivers,and the effects of different driving behaviors on traffic flow are studied.In addition,considering ACC vehicles and manual driving modes,a mixed traffic flow model was established to verify the positive effect of ACC vehicles on traffic flow.Traffic simulation based on CA model fully supports the customization of driving be havior,road conditions and simulation accuracy,which is easy to modify and has strong adaptability.Simulation with CA model can avoid the approximation process of "discrete"-"continuous"-"discrete".There are several practical applications of researches in this t hesis:1)traffic management and speed control in adverse weather;2)driver training and management;3)traffic violation management and education for drivers;4)application of automatic driving technology.To sum up,this work has a complete theoretical basis an d broad practical prospects,which is of great significance to the development of road tra ffic system.