The line from Grong to Bodø was passed as part of a national railway plan approved by Parliament on 17 November 1923. This involved first building the section from Grong to Mosjøen. The detailed plans were split between two routes, the first from Storforsen til Mosjøen approved the following year and the rest of the line in 1926. Due to high unemployment, work on sections at Spelruem and Gullsmedvik started in late 1923. The main route discussion involved where to run the line immediately north of Grong, where a detour was rejected which would have cut the length of the Medjå Tunnel. Grong received a station above the town in order to avoid clay deposits. Also in Brekkvasselv there were two route alternatives.