The Drammen Line was converted to dual gauge between 1917 and 1920, and then only standard gauge from 13 November 1922. The Drammen Line was electrified in two stages, in 1922 and 1930. The Bratsberg Line opened between Notodden and Skien in 1917, and the section of the Vestfold Line from Skien to Eidanger was converted to dual gauge. From 16 June 1921 the line, including the branch to Brevik, was entirely standard gauge. This caused the trains from Skien and Porsgrunn to be re-routed via the Bratsberg Line Kongsvinger to Oslo.