Southern Cross-Island Highway (Provincial Highway 20) is 208 kilometers long. It starts in Tainan and ends with Degaolu Bridge in Guanshan Township of Taitung County, connecting with Provincial Highway 9. About one-third of the entire route passes through Tainan, Yongkang, Sinhua, and other densely populated areas.
The section from Nanhua Reservoir in Nanhua District of Tainan City to Jiaxian District and Liugui District in Kaohsiung City leading to the mountain area is known as the Southern Cross-Island Highway. Completed to open for traffic in 1972, the western section of the highway goes along Laonong River and the eastern section runs along the Beinan River valley. Joints on the rock walls can be clearly seen. The rock walls are severely weathered and the geology is rather fragile. The pavement built close to steep mountain walls and river terraces would experience landslides from heavy rain or be washed away by flash floods, which interrupt traffic. After being heavily damaged by the rain carried by Typhoon Morakot on August 8, 2019, the section between Tianchi and Xiangyang on the eastern section of Southern Cross-Island Highway has not yet been fully repaired.
The 30-kilometer section between Meishankou and Wukou on Southern Cross-Island Highway is within the area of Yushan Nation Park. The road winds in alpine ravines and ancients forests and pass through many magnificent landscapes such as mountains, rocks, streams, and forests. It is an important access road for the southern part of Yushan National Park. Many visitors travel between the attractions along the highway to participate in various recreational activities.