本文旨在探討臺灣地區，柔性路面設計中對環境因子包括氣溫、降雨乃至地文、天文等自然條件應做的考量。本研究除彙整回顧環境影響情況、本省環境型態以及常用設計法之環境因素處理外，並將中央氣象局所發布的全省氣溫、降雨資料分為北、中、南及東部四區，依各地降雨強度及降雨稠率，配合地域環境條件換算各地的排水品質及係數供ＡＡＳＨＴＯ法設計使用。另建議區域因子係數（ｋ’）和排水品質指標值的對等關係供Ｒ值設計法使用，同時提供機土壤和瀝青混凝土隨飽和度、溫度增高之模數衰減數學校正式，供道路設計參考。該項校估程序可適用於任何設計法，有效地反應現地材料在臨界環境狀態下所顯現的承載力。 In this paper, environmental factors affecting the thickness design of the flexible pavement are discussed. Design methods commonly used in Taiwan are presented with local information of climate, rivers, topography and geology. According to thirty-year surface data from the Central Weather Bureau in ROC, the mean and the absolute maximum/minimum temperature as well as the precipitation and the number of the days with precipitation are reanalyzed for four different design districts. Localized drainage coefficients of the base and subbase layers of the flexible pavement, which are used in the AASHTO method, are proposed for these districts. Moreover, drainage quality of a paving site can be determined with the correlation of few environmental factors using the suggested designation numbers. Mater corrections considering the temperature and moisture influences on the AC surface and subgrade soils are recommended for most of the available design methods.