Modeling the Effects of Rainfall on Urban Freeway Free-Flow Speeds

摘要

This paper presents an investigation of the effects of rainfall with varying precipitation intensity at every millimeter interval on urban freeway free-flow speeds. The traffic data and corresponding weather information data from the Inner Ring in Shanghai for more than one year were used. Statistical and regression analysis were applied to investigate the effects quantitatively. There are three major contributions of this paper. Firstly, statistical analysis indicates that the rainfall does not significantly affect the speeds variability until the flow rate reaches to a certain level, such as 400veh/h/ln in this study. Secondly, the variation pattern of mean speeds at every millimeter interval of precipitation intensity was investigated. Thirdly, it is the first study to model the effects of precipitation intensity at every millimeter interval on free-flow speeds. Both piecewise linear model and natural logarithm model were used to model the effects of precipitation intensity. By comparing the two models, the piecewise linear model is proposed in this study.