Study On Capacity Of Urban Expressway Use Simulation Under The Condition Of Traffic Accident

Urban express way is the main artery of urban traffic, so that traffic accidents on it may cause traffic jams both on the road section and the whole road network. If the capacity under the condition of traffic accident can be measured accurately, then the diversion in the upstream can be guided quantitatively, which can avoid huge secondary traffic jams and make the capacity of the road network be fully utilized. Capacity estimating methods which use parametric and non-parametric approaches have some disadvantages in the application, therefore, this thesis intends to do the simulation study of the capacity estimating of urban expressway under the condition of traffic accidents.Firstly, this thesis reviewes the literatures of traffic capacity and microscopic traffic simulation, emphatically expounds the research status quo of traffic capacity under the condition of lanes taking-up, and parameters calibration of microscopic simulation which is the core step of simulation. Based on the summary of current research, this thesis selects VISSIM as the simulation software, and intends to use genetic algorithm to calibrate the parameters.Secondly, this thesis defines the sections of the accidental road, and analyzes the characteristics of drivers’ behaviors and vehicles’ behaviors on the accidental road. According to the summary of the influential factors of traffic capacity, this thesis constructs the concept model of traffic capacity under the condition of traffic accident, then transforms parameters of concept model to the simulation model and builds the framework of using simulation technology to estimate capacity. This thesis discusses one of the cores of the framework, i.e. how to simulate the accident condition, and designs the dynamic adjustment program of VISSIM driving behavior parameters.Thirdly, this thesis studies another core of the framework, i.e. simulation parameters calibration.It establishes the travel time as calibration indicator of simulation model of accident section, uses the single factor displacement method for sensitivity analysis of the simulation parameters, selects parameters set and their value range, and on these basis, this thesis designs the calibration program using MATLAB. Finally, this thesis chooses a typical one-way three-lane and one-way four-lane rear-end accidents as cases study. The relative error between the simulation result and survey result of capacity of both the two cases are smaller than5%, which indicate that the framework is effective. Meanwhile, by simulating the different accident condition, the capacity and its reduction factor of one-way three-lane and one-way four-lane urban expressway under different accident roadway taking-up number and length is calculated. The result shows that the relationship between capacity of road accident and roadway taking-up length is a linear negative correlation and along with the growth of the number of roadway taking-up, the capacity falling gradient is slow down. By using the one-way three-lane simulation model, the amount of traffic evacuation under different accident time is analyzed. Based on the time distribution regularities of traffic evacuation, the matters and attentions of upstream traffic diversion are qualitatively discussed.