The Sognsvann Line () is a rapid transit line on the Oslo Metro of Norway. It branches from the Common Tunnel at Majorstuen and runs to Sognsvann. After Ullevål stadion, the Ring Line branches off. The Sognsvann Line serves the northwestern and northern neighborhoods of Oslo, mostly within the borough of Nordre Aker. The line is owned and maintained by Kollektivtransportproduksjon and has nine stations. The western end of line 5 serves the entire line. Line 4 and the eastern end of line 5 serve the southern part of the line up to Ullevål stadion before branching off and continuing along the Ring Line. This gives an average five-minute headway on the southern part and an average fifteen-minute headway on the northern part of the line. The line opened on 10 October 1934 as a light rail. In 1993, it was upgraded to metro standard as the first light rail west of Oslo, with two stations being closed. The Ring Line opened in 2003. Forskningsparken has transfer to the Oslo Tramway and serves Rikshospitalet. Forskningsparken and Blindern both serve the University of Oslo, while Ullevål stadion serves Norway's largest football venue. North of there the line mainly serves residential areas. Sognsvann serves the Norwegian School of Sport Sciences and the recreational area Nordmarka. History The first plans for a light rail along the route of the Sognsvann Line were launched by Holmenkolbanen in 1904. They called for a branch from Gaustad Station on the Holmenkoll Line to Geitmyren and onwards to Sagene. The next proposal for a line was launched in 1917, when Aker Municipality established the company Akersbanerne. It started work planning the Østensjø Line as well as the Sognsvann Line. The neighborhoods of Sogn and Tåsen were being built, and the municipality wanted to establish a good transport system to make the areas more attractive. Holmenkolbanen stated that they should be prioritized to build the system, since they already had a line in the area, but the municipality wanted to have political control over the development of the area. In 1920, Holmenkolbanen applied to build a branch from Frøen via Tåsen to Nydalen and Grefsen, along what is today the Ring Line. This proposal included a branch to Sognsvann. The Ministry of Labour granted the concession to Akersbanerne, who started construction in January 1922. However, due to a labor conflict, the work was put on hold in 1924.