southwards and runs to Godlia Station, which is located on an elevated section of track. It continues for past Skøyenåsen Station and then to Oppsal Station. Next the line runs through a tunnel under Haakon Tveters vei and Østmarkveien. It passes Ulsrud, before it starts running parallel to General Ruges vei and passes Bøler and Bogerud Stations. Immediately afterwards it runs through a tunnel and continues onwards to Skullerud Station. The line then runs along a section, consisting of a tunnel, a bridge over Ljanselva, a tunnel, a bridge over Vinterveien, and then the rest of the section in a combined concrete and bedrock tunnel to Mortensrud Station. Service The Østensjø Line proper is served by Line 3 of the Oslo Metro. On weekdays there are eight trains per hour most of the day. This is reduced to four trains per hour during late evenings, the summer vacation, and weekends. Line 3 runs through the Common Tunnel and continues along the Kolsås Line to Kolsås. Operations of the lines are done by Sporveien T-banen on contract with Ruter, the public transport authority in Oslo and Akershus. The infrastructure itself is owned by Sporveien, a municipal company. Service is provided using MX3000 three- and six-car trains. Travel time from Mortensrud to Brynseng is 17 minutes and from Mortensrud to Stortinget is 27 minutes. The line had 11,643 weekday average boarding passengers in 2002, making it the third-most heavily trafficked of the eastern metro lines. History Construction The area around Etterstad was originally connected to the city center via the Vålerenga Line and then the Gamlebyen Line of the tramway. The Vålerenga Line was built and operated by Kristiania Sporveisselskab (KSS), which had opened the line on 3 May 1900. Proposals for a link from Etterstad towards the Østensjø area were first articulated in 1917. That year Aker Municipality established the municipal tramway company Akersbanerne to build light rails to the Aker suburbs of Oslo. Meanwhile, Aker and Oslo had issued a contest for a network of tramways throughout the urban area. The winning design, made by Jørgen Barth, included a series of suburban lines, including one to Østensjø. This resulted in a municipal urban rail plan that was passed in 1919. Construction started in February 1922, and by 18 December 1923, construction had come far enough the section from Etterstad to Bryn could open. An agreement was made with KSS, where