During construction of a level crossing at Smørstein on 17 August 1918 the area around the track started experiencing a series of landslides. Within a few days the earthwork under the tracks had slid away. Vy hired a steamship to freight passengers and cargo past the effected area, and part of the traffic was freighted across the fjord from Horten to Moss. A temporary line was built close to the mountain, while construction took place of a temporary solution, the Smørstein Tunnel. The temporary line opened on 28 October 1918 and the new segment with a tunnel on 25 May 1921.