Accompanied by rivers and ravines: These secondary lines follow the same direction as the island's rivers and streams, each of them winding through a valley. The Pinghsi line runs by the Keelung River. The Neiwan line tracks the Touchien and the upper reaches of the Yulo. And the Chichi line runs alongside Taiwan's longest river, the Choshui and its alluvial plain.
這些支線與台灣的河流走向相同，每一條支線都循河谷而行，平溪線與基隆河相依；內灣線旁是頭前溪和其上游油羅溪；集集線則走在台灣最長的河流﹘﹘濁水溪的沖積平原上。