 The decision to build the T-bane was made by the city council in 1954; the Østensjø Line would be converted to metro standard, and three new lines would be built, with the Lambertseter Line opening as a suburban line on 28 April 1957.The first closing of tram lines occurred in 1949; on 17 January the line to Korsvoll was closed, followed on 6 February the line to Rodeløkka.The line to Rodeløkka was not removed, and a new line opened on 2 January 1955.