For the construction of the Lötschberg line and the main tunnel two special construction railway had to be constructed to bring material from Frutigen or the junction at Naters near Brig to the portals of the Lötschberg tunnel. The gauge of the railways was , the maximum gradient was 60 per thousand (6%) and the minimum curve radius was . While on the northern approach the construction line was built on a different route to the permanent line, on the south side the construction line followed the permanent line to a large extent.