Study On Car-following Model Of Snow And Ice Covered Urban Expressway

With the development of the society，the influences of urban traffic congestion andsafety on people’s normal life become more serious. In winter, especially in the northarea of our country, the traffic problem caused by snow and ice is particularlyoutstanding. Investigating basic theory of traffic flow to develop the potential ruleprovides the foundation for doing traffic management and alleviating traffic problem.As an important branch of the traffic fundamental theory, the research of car-flowingmodel in snow and ice urban expressway yields very important practical significance.First, this paper classifies urban roads based on their surface conditions in winter,and then conducts traffic surveys on two common snow and ice roads, combined withthe actual situation of urban expressway. According to the results of the surveys, thispaper analyzes statistically on traffic flow characteristics, such as free flow rate, averagespeed, speed distribution, headway between adjacent vehicles, the relationship betweenrelative speed and headway, and the driver’s reflection characteristics, and thenquantitatively studies the influences of ice and snow on car-following behaviors inurban expressway.Secondly, this paper compares and analyzes the characteristics of different types ofspeed optimization function, establishes predicted speed model according toGreenshields speed-density relationship, then constructs the minimum distances modelaccording to car-following state, thus builds snow and ice road speed optimizationmodel. Based on the present research theory of car-following, using the ideology oflinear car-following model to optimize full speed difference model, and combining withthe speed optimizing function, this paper establishes a new car-following model whichis suitable for snow and ice urban expressway.Finally, the model is calibrated relying on the experimentally measured data, andexperiments are designed to verify the model stability, and acceleration asymmetry. Inthe meanwhile, the simulation and analysis on the new model and the full speeddifference model based on the survey data, show that the new model agrees better withthe actual traffic flow in ice and snow roads, which can provide theoretical support forformulating icy and snowy traffic management.