The route is also known as
Zhongfeng Highway (中豐公路) between
Longtan and
Fengyuan,
Zhongtan Highway (中潭公路) between central
Taichung City and
Caotun, and
Yunmi Armaments Road (澐密戰備道路) 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 the
Executive Yuan. After a brief concurrency with
PH 1 along Zhongxiao West Road (忠孝西路), highway 3 continues along Zhonghua Road (中華路) and Heping West Road (和平西路) before leaving for
Banqiao in
New Taipei City via the Huajiang bridge (華江橋). In Banqiao the highway is known as Wenhua Road (文化路), 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 (中山路) and Sichuan Road (四川路) towards
Tucheng. The road goes through downtown Tucheng and bypassing downtown
Sanxia before entering
Taoyuan City. In Taoyuan the highway passes through old town
Daxi, which is also the terminus of North Cross-Island Highway (北部橫貫公路), 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 alternative to Freeway 3, passing through the rural parts of
Guanxi,
Hengshan,
Zhudong,
Beipu,
Emei, and continues to
Miaoli County. In Miaoli the highway has 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 (中部橫貫公路), 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 (中山路), Beitun Road (北屯路), Jinhua Road (進化路), and Jiancheng Road (建成路). 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 bypasses downtown
Douliu. After passing through
Gukeng the highway enters
Chiayi County. In Chiayi the highway connects the mountainous towns of
Meishan,
Zhuqi,
Fanlu,
Zhongpu, and
Dapu. Beginning from Zhongpu to Nansi, the highway becomes a winding mountainous road known as the
Yunmi Armaments Road (澐密戰備道路), as the road was initially built for wartime preparations. The highway passes through the
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 the Southern Cross-Island Highway (南部橫貫公路). Highway 3 then enters
Kaohsiung City, passing through the downtowns of mountainous districts of
Neimen and
Cishan. Highway 3 then goes through
Jiuru and
Ligang in
Pingtung County before ending at the intersection with
PH 1 in
Pingtung City. ==Spur Routes==