Wang, Yamamoto, Miwa and Morikawa 1 An Analysis of Effects of Rainfall on Travel Speed at Signalized Surface Road Network Based on Probe Vehicle Data Lixiao Wang 1 , Toshiyuki Yamamoto 2 , Tomio Miwa 3 , Taka Morikawa 4 ABSTRACT The rainfall effect on the travel speed is investigated for a signalized urban surface road network by using probe vehicle data and rainfall data. The data sets were obtained from the central area of Nagoya City, Japan in May and June 2004. The results show that as the rainfall becomes heavier, the average travel speed becomes lower significantly. In the case of heavy rain, the average travel speed decreases 6.03 km/h when compared to the case of no rain. However, the size of the effects varies across the hierarchy of the road, the number of lanes, and the travel speed at no rain. We can now provide more accurate travel time forecasts at signalized urban surface road networks by considering these factors when the weather forecasts are obtained. KEYWORDS: rainfall, probe vehicle data, travel time, travel speed, regression model. INTRODUCTION How to relieve traffic congestion and reduce the effects on the environment of the road traffic have become very important in Japan. The economic loss of 12 million Japanese yen is caused by the traffic congestion every year, and then the average time loss is about 42 hours per person per year. However, it is difficult to construct more roads to solve these problems. Therefore, more efficient use of the existing roads becomes the main direction for realization of the environment-friendly transportation 1 Doctor Candidate, Graduate School of Environmental Studies, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan. Tel: 0081-52-789-3730; e-mail: wang@trans.civil.nagoya-u.ac.jp 2 Associate Professor, Dept. of Civil Engineering, Nagoya University, e-mail: yamamoto@civil.nagoya-u.ac.jp 3 Research Specialist, Graduate School of Environmental Studies, Nagoya University e-mail: miwa@civil.nagoya-u.ac.jp 4 Professor, Graduate School of Environmental Studies, Nagoya University, e-mail: morikawa@nagoya-u.jp