The cost went up, however, mainly as a result of inflation and the extra work needed to cope with the difficult terrain. An extra year also had to be added to the timetable to allow for hold-ups caused by bad weather, and the construction of the many bridges and tunnels along the 81.6-kilometer route.
北迴鐵路總長雖然只有八一．六公里，但是由於工程都在群山或急湍中進行，有一半以上的路線是大大小小的隧道和橋樑。本來逢山開洞、遇水架橋是構築鐵路的原則，但是東部山區的氣候、土質與地形實在太壞，使得工程整整花了六年才完工，其中經歷的辛酸困苦，遠非外人所能想像。