With the conversion to metro standard, the 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.