page_title: Kolsås Line
section_title: Underground connection
hierarchical_section_title: Kolsås Line / History / Underground connection
caption_attribution_description: Norsk bokmål: Oslo Sporveier, C1 301 og nok en C1 passerer planovergangen. English: C1 301 at Sørbyhaugen on the Oslo Metro's Røa Line
context_page_description: The Kolsås Line is a 12.1-kilometer line of the Oslo Metro. It branches off from the Røa Line at Smestad Station and runs through western Oslo and Bærum to Kolsås Station. It serves the neighborhoods of Ullernåsen, Øraker, Jar, Bekkestua, Haslum, Gjettum and Kolsås. It is served by Line 3 of the metro at a 15-minute headway. The section from Jar to Bekkestua is built as a dual system with overhead wires, allowing Line 13 of the Oslo Tramway to continue from the Lilleaker Line to Bekkestua every ten minutes.
  The Kolsås Line was built as an extension of the Lilleaker Line. It had been built to Lilleaker in 1919. The line was extended to Avløs on 1 July 1924, and the line was extended to Kolsås on 1 January 1930. The line was initially owned by Bærumsbanen, which was bought by Oslo Sporveier in 1934. A connection to the Røa Line opened on 15 June 1942, allowing the line access to the Common Tunnel. At this point the section from Sørbyhaugen to Kolsås was designated the Kolsås Line, while the section from Jar to Skøyen was retained as the Lilleaker Line. T1300 trains of the metro were introduced in 1982 and from 1995 it was linked with the eastern metro lines.
context_section_description: Since the birth of the line, plans had existed to connect to the Common Tunnel of the Holmenkollen Line. The tunnel would allow the trams to operate straight to the city center at Nationaltheatret, giving faster travel times and removing the heavy Class A trams from the city streets. A plan for the route from Jar to Sørbyhaugen on the Røa Line had been made in 1919, but by the 1930s, the Norwegian Radium Hospital and a tuberculosis hospital at Ullern had been built in the immediate vicinity of the line. Concession for this route was granted on 30 April 1937, but Aker Municipality protested, because they did not want noise pollution at the hospitals. Another concern was that the magnetic field from the overhead wires could affect the instruments at the hospitals. The route was therefore moved, but this made construction more difficult due to worse geological conditions.
  Construction started in 1939, but was put on hold in 1940 because of the break-out of the Second World War. Construction resumed in April 1941 and later the same year the first Class C trains were put into service. The work also involved widening the profile between Jar and Egne hjem so the Class C could operate on the whole length of the line. The connection from Jar to Sørbyhaugen opened on 15 June 1942. Double track was installed from Haslum to Kolsås; this opened on 23 December. A further six Class C were delivered, matching loading gauge of Holmenkolbanen's lines. In addition, two Class A trams were converted to the wider and longer Class D.
  With the opening of the connection, the 16.4-kilometer (10.2 mi) section from Sørbyhaugen to Kolsås was designated the Kolsås Line, and the 3.8-kilometer (2.4 mi) section from Jar to Skøyen was designated as the Lilleaker Line. A balloon loop was built at Jar, allowing the new Class B trams that served the Lilleaker Line to turn there. This allowed for transfer between the two lines. The distance from Kolsås to Nationaltheatret was 16.4 kilometers (10.2 mi). During World War II, ridership on the whole tramway, including the Kolsås Line, skyrocketed. The line transported 5.7 million passengers in 1938, while in 1944 it transported 19 million. Ownership of rolling stock and all but two employees in Bærumsbanen were transferred to Oslo Sporveier in 1944. However, the ownership of the tracks and the formal operation rights remained with Bærumsbanen.
caption: Class C1 tram at Sørbyhaugen in 1978, the station where the Kolsås Line branches off from the Røa Line
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