In 1942, the Sørbyhaugen–Jar Line was opened, which connected the Kolsås Line with the
Røa Line. On 5 July 1957, the southbound station
Mærradalen was closed and
Ullernåsen was moved midway between its old location and that of Mærradalen. On 19 June 1961, Husebybakken was closed. In 1995, the
Røa Line, which the Kolsås Line branches off from, was upgraded to
metro standard to allow trains to operate through the
Common Tunnel in the city tunnel. The first section of the Kolsås Line, from the branching point to Montebello was also upgraded. Trains switched from overhead wire to third rail at Montebello. By early 2006, the
Akershus County Council passed an upgrade plan for the Kolsås Line. It would be upgraded to metro standard all the way to Kolsås, and while under construction, the sections of the line not yet upgraded will remain closed. The first section be upgraded, was from Montebello to
Åsjordet. Because the upgrade included an extension of the stations to allow six-car trains, Montebello would need to be closed. Since the track until Montebello had full metro standard, building a temporary station in the area would allow the area to be served by the T-bane, and at the same time give the trains on line 6 a turning station. Husebybakken was closed on 31 May 2008. The line did not reopen until 18 August, when the three first stations were finished upgraded to metro standard: Montebello,
Ullernåsen and Åsjordet. During the intermezzo, trains turned at
Holmen on the Røa Line. Following its closing, Husebybakken was demolished. ==Service==