Modeling Expressway Travel Time Under Rainfall Conditions Based on GPS Data

Empirical studies have suggested that rainfall affects travel time. This study presents an investigation of the effects of rainfalls with different levels of precipitation intensity on expressway segment travel time with the variation of traffic flow rate. More than 1 year’s GPS data, traffic volume data and corresponding weather information data from Luoshan expressway segment located in Shanghai Pudong New Area were used for this study. First, a direct method is proposed to obtain the expressway segment average travel time aggregated in 5 min with GPS data from floating cars. Then, a modified BPR function is developed to fit the relationships of average travel time and traffic flow rate under rainfalls with different levels of intensity. The parameters of modified BPR function are calibrated under good weather, slight, moderate and heavy rain conditions respectively. The result demonstrates that average travel times generally get longer as well as more instability when the rainfall is heavier under the similar traffic flow rate condition.