The South Cross-Island Highway is one of the major channels that bridges the southern and eastern part of Taiwan. The highway with a total length of 209 km starts from Tainan City, running through complicated geology structures, fragile stratum and special topography along the Central Mountain range, then end of Hai-Duan Hsian, Taitung County. The heavy rainfalls brought by the annual typhoon and monsoon season has been recognized as a major factor triggering collapse and slide of hillslopes along the highway. The disasters mentioned usually jeopardize the traffic line.
To investigate the slope failures along the highway, the Geographic Information System (GIS) and Remote sensing (RS) has been adopted to establish a database system of slope failures. Being alocated by using Global Position System (GPS) technique, the 84 slope failures predomimantly happen on the western and northwestern facing slope having the elevations within 1500 to 2000 and 500 to 1000 meters and the dip between 60 to 70 degrees. The major types of slope failures include runoff erosion and rock fall. Also, slides on the down slope arise lose of highway pavement. Newly collected geo-environment and natural environment data being integrated with a database system established in past years to form a complete database for the highway. Multivariate analysis intaking the failure factors such as slope aspect, dip, and fault locations etc. is used to evaluate the risk of slope failures for different locations along the highway. Based on the results, the western branch of highway belongs to low risk zone and the eastern section of the highway is classified as moderate to high risk section. The former results are mainly due to the Pilushan Formation and Tananao Schist zone in the east band of the highway. The results of this research could help planning and designing of dister prevention engineering construtions along the South Cross-Island highway in the near future.