[citation needed] On 19 November 2016, JR Hokkaido's president announced plans to rationalise the network by up to 1,237 km, or ~50% of the current network,[1] including the proposed conversion to Third Sector operation of the Tomakomai–Iwamizawa section of the Muroran Main Line.

The section between Oshamambe and Numanohata is the part of the main link route between Sapporo and Hakodate.

The last section was once an important freight route, but became a quiet local line after coal mines closed.

In 1892, the Hokkaido Colliery and Railway Company opened the line from Muroran (now Higashi-Muroran) to Iwamizawa.

The line was built to link coal mines in the Iwamizawa-Asahikawa region and Muroran Port.

The last steam locomotive hauled regular service ran between Iwamizawa and Muroran in 1975.