Østensjø Line was converted to having third rail power supply, the platform height was raised and the platforms lengthened to to handle six-car trains. All level crossings were removed. The Lambertseter Line was the first line of the Oslo Metro when it opened on 22 May 1966. Instead of following the Vålerenga Line to the city center, it instead followed the Common Tunnel from Brynseng to Jernbanetorget. From 19 June 1967 Line 3 stopped being linked with the Lilleaker Line and only ran to Jernbanetorget. The line was closed during the evening of 25 October. From 28 October 1967, the line was connected to the metro and T1000 started being used on the service. The three days were used to remove the balloon loop at Bøler and connect the line to the Common Tunnel. The extension from Bøler to Skullerud opened on 26 November 1967. Metro operations Services on the Østensjø Line were carried out by Line 3, originally running from Skullerud to Jernbanetorget in the city center. The fourth line of the metro was the Furuset Line. Its initial opening took place on 18 November 1970, when services with Line 6 commenced to Haugerud. The city center service was extended to Sentrum on 9 January 1977. However, this station was closed from 20 March 1983 to 7 March 1987, and reopened as Stortinget. 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. The Sognsvann Line was converted to a metro line from 8 April 1995, allowing Line 3 to continue onwards to Ullevål stadion from that date. The line has received one extension after the metro conversion. Additional housing in the Mortensrud area resulted in plans to a metro connection to the area. Also the Lambertseter Line was considered to be extended to the area, but the Østensjø Line was eventually landed upon. Initial plans called for construction to commence in 1992 and be completed in 1994. However, construction did not start until 1995. The extension is built to allow speeds of , and represents a considerable longer distance between stations than what is normal on the network. Most of the section is in tunnels, though there are also two viaducts. The extension, excluding the new station, cost 215 million krone. The station cost 35