Also known as Inner-Mountain Highway (內山公路), the road travels through mountainous towns in Western Taiwan and was the major route for the area until Freeway 3 was built.

In Hsinchu the highway serves as a scenic alternative to Freeway 3, passing through the rural parts of Guanxi, Hengshan, Zhudong, Beipu, Emei, and continues to Miaoli County.

The highway passes through mountainous townships of Shitan, Dahu, and Zhuolan before entering Taichung City.

The highway then exits central Taichung and enters the southern suburbs of Dali and Wufeng before leaving for Nantou County.

In Chiayi the highway connects the mountainous towns of Meishan, Zhuqi, Fanlu, Zhongpu, and Dapu.

The highway passes through the Zengwen Dam in Dapu, the largest reservoir in Taiwan by volume, and enters Nansi in Tainan City.