The highway begins at Xibin Expressway (西濱快速道路), also known as PH 61, in the coastal township of Houlong.

The highway closely follows Houlong River, passing through junctions with PH 1, Freeway 3, PH 13 as it reaches Miaoli City.

The highway continues to head south towards Gongguan, where it meets Freeway 1.

Highway 4 reaches its terminus at an intersection with PH 3 at the border of Shitan and Dahu townships.

http://www.thb.gov.tw/ (National Highway Bureau, in Traditional Chinese) This Taiwanese road or road transport-related article is a stub.