The route is also known as Zhongfeng Highway between Longtan and Fengyuan, Zhongtan Highway between central Taichung City and Caotun, and Yunmi Armaments Road between Zhongpu, Chiayi and Nansi in Tainan City. Since the highway runs roughly parallel to Freeway 3 for the majority of its length, it is now primarily a highway providing local access as well as a scenic alternative route to the freeway. The highway begins in Taipei City near Executive Yuan. After a brief concurrency with PH 1 along Zhongxiao West Road, highway 3 continues along Zhonghua Road and Heping West Road before leaving for Banqiao in New Taipei City via Huajiang bridge. In Banqiao the highway is known as Wenhua Road, one of the busiest roads in the district. At Banqiao Station, the road had a brief concurrency with County Route 106 before turning south as Zhongshan Road and Sichuan Road towards Tucheng. The road goes through downtown Tucheng and bypassing downtown Sanxia before entering Taoyuan City. In Taoyuan the highway passes through old townDaxi, which is also the terminus of North Cross-Island Highway, or PH 7. After a brief concurrency with PH 4, the highways split in Daxi. Highway 3 continues southwest to Longtan before entering Hsinchu County. In Hsinchu the highway serves as a scenic alternate to Freeway 3, passing through the rural parts of Guanxi, Hengshan, Zhudong, Beipu, Emei, and continues to Miaoli County. In Miaoli the highway had a brief concurrency with County Route 124 in Sanwan before highway 3 splits and continues south. The highway passes through mountainous townships of Shitan, Dahu, and Zhuolan before entering Taichung City. In Taichung highway 3 passes through more mountainous districts in Dongshi, which is also the terminus of Central Cross-Island Highway, also known as PH 8, and Shigang before entering Fengyuan, a suburb in northern Taichung. The highway then becomes an urban road, going through the suburb of Tanzi and central Taichung as Zhongshan Road, Beitun Road, Jinhua Road, and Jiancheng Road. The highway then exits central Taichung and enters the southern suburbs of Dali and Wufeng before leaving for Nantou County. Highway 3 is an important highway in Nantou, connecting Caotun and Nantou City, the two main population centers in the county. The highway then passes through Mingjian and Zhushan before entering Yunlin County. In Yunlin the highway goes through Linnei and bypassing downtown Douliu. After passing through Gukeng the highway enters Chiayi County. In Chiayi the highway connects the mountain towns of Meishan, Zhuqi, Fanlu, Zhongpu, and Dapu. Beginning from Zhongpu to Nansi, the highway becomes a winding mountainous road known as Yunmi Armaments Road , as the road was initially built for wartime preparations. The highway passes through Zengwen Dam in Dapu, the largest reservoir in Taiwan by volume, and enters Nansi in Tainan City. In Tainan City, the highway goes through Nansi, Yujing, and Nanhua. The highway has a concurrency with PH 20 from Yujing to Nanhua before the latter turns east and becomes Southern Cross-Island Highway. The highway then enters Kaohsiung City, passing through the downtowns of mountainous districts of Neimen and Cishan. Highway 3 goes through Jiuru and Ligang in Pingtung County before ending at the intersection with PH 1 in Pingtung City.
: The route goes from Highway 3 in Zhushan, Nantou to County Route 152 in Jiji, Nantou. The highway provides access from the parent route to the township of Jiji. The total length is 7.124 km.
