[2] In 1923 the privately owned Sinhŭng Railway opened the mainline of its Hamnam Line (not to be confused with the line of the same name of the Chosen Magnesite Development Railway, nowadays called Kŭmgol Line), from Hamhŭng to Sinhŭng via Oro (nowadays called Yŏnggwang), and subsequently expanded the line with the addition of a branch from Oro to Sangt'ong that was opened on 1 October 1926.

In 1934, to aid in the construction of a new hydroelectric power plant on the Changjin River, and to exploit forestry and other resources in the area, the Sinhŭng Railway began opening its Changjin Line.

Although significant for passenger transport in the area, the bulk of the trains on the Changjin Line are for freight transport, with the majority of traffic being outbound cargo - in the mid 1980s, 62.1% of all freight traffic originated on the line for shipment elsewhere, while only 37.9% being traffic from elsewhere destined for points on the line.

Of inbound goods, coal is the most important at 36.7% of the total (of which up to 20% is anthracite), followed by rice and other grains (18.9%), fertiliser (11.9%), sea products (8.2%) and cement (4.2%).

[2] A yellow background in the "Distance" box indicates that section of the line is not electrified; a pink background indicates that section is 2 ft 6 in (762 mm) narrow gauge; an orange background indicates that section is non-electrified narrow gauge.