 The line from Sandvika to Oslo was substantially upgraded between 1917 and 1922 . From 27 February 1917 a passing loop was built at Lysaker and standard gauge traffic was carried out on the northern track . A southern track was then built , which was used by narrow gauge trains . However , both were dual gauge . All – standard gauge operations commenced on 9 February 1920 , although the dual gauge was not removed until 1922 . Electric traction started operation on 30 August 1922 . An interlocking system was installed on 29 July 1924 . From 1922 a half @-@ hour headway was introduced on the local trains between Sandvika and Oslo West Station . 
