the night between 17 and 18 May 1966, in preparation for the conversion to metro. The line was disconnected with the tramway at Høyenhall and instead to the new metro line that leads to the Common Tunnel. At Bergkrystallen the loop was removed and the tracks rebuilt. All the platforms had in due time been rebuilt to the platform height used by the metro. The Lambertseter Line opened as the first part of the Oslo Metro on 22 May 1966, along with the Common Tunnel. In October the Grorud Line was connected, and in 1967 the Østensjø Line. With the upgrade, T1000 rolling stock was taken into use, along with automatic train control, step-free access with high platforms and a third-rail power supply. On 9 January 1977, the city center service was extended to Sentrum. However, this station was closed from 20 March 1983 to 7 March 1987, and reopened as Stortinget. At first the line had a headway of 15 minutes. From 21 August 1978 this was halved to 7.5 minutes during rush hour, some from Bergkrystallen and some from Karlsrud. During the last years of the 1980s the barres and payment stalls were removed and replaced with a proof-of-payment system. This unmanning of the station allowed for a significant cut in operating costs. On 4 April 1993 the Sognsvann Line was converted to a metro line and it was linked with the Lambertseter Line and Line 4. With the delivery of T2000 trains, the Holmenkollen Line and Line 1 was also routed to the Lambertseter Line, although outside of rush hour Line 1 did not run past Helsfyr. This was changed from 12 April 2003, when Line 4 was linked with the Kolsås Line, and Line 1 no longer ran along the Lambertseter Line. Services on Line 1 resumed on 8 August 2005. From 20 August 2006 this was changed and Line 4 connected instead with the Ring Line. From March to 6 December 2010 the Holmenkollen Line was closed for upgrades and Line 1 was terminated. Oslo T-banedrift was in the process of taking delivery of new MX3000 trains, but they did not yet have sufficient matériel to use six-car trains on the Lambertseter Line. The abrupt reduction in service caused there to be standing-room only from Munkelia. Further deliveries of MX3000 allowed several of the trains to be extended to six cars. An express bus line,