The Effects of Rainfalls on Expressway Travel Time

This paper presents an investigation of the effects of rainfall with different levels of precipitation intensity on urban expressway travel time under free-flow speed conditions. The traffic data and corresponding weather data from the expressway section of Longyang in Shanghai for more than one year were used. Statistical analysis was applied to investigate the effects of rainfall on travel time quantitatively. There are two major contributions of this paper. Firstly, four levels of rainfall have varying degrees of significant impacts on travel time in terms of average travel time. Slight rain has no influence on variability of travel time, while heavier rain increases the variability. Secondly, three travel time stochastic models: Normal, Lognormal and Weibull, were proposed. The Lognormal model is the best-fit model under good weather, slight and moderate rainfall conditions, while both Weibull model and Lognormal model are the preferable models under heavy rain and rainstorm conditions. The recommended Lognormal model can be further used for evaluating the performance of the Longyang expressway section in terms of travel time reliability under good weather, slight rain, moderate rain, heavy rain and rainstorm conditions respectively.