to Nationaltheatret; the line was opened in 1928 (and was then only the second underground railway to be opened in the Nordic countries after Boulevardtunnlen in Copenhagen which opened in July 1918 ), with one intermediate station at Valkyrie Plass, giving the two suburban lines access to the central business district of Oslo. The success of the suburban lines tempted KES to extend their streetcar service west from Skøyen as a suburban line; the Lilleaker Line opened to Lilleaker in 1919, to Avløs in 1924 and to Kolsås in 1930. A new section from Jar to Sørbyhaugen opened in 1942, connecting the line from Jar to Kolsås to Nationaltheatret, and making it a rapid transit and the replacement of stock with wide suburban standard. This service remained part of the municipal Oslo Sporveier, that had bought all the streetcar companies in 1924. Compensation for large amounts of damage to houses along the route during construction, along with higher construction costs than calculated was a heavy burden on the company, and in 1934, the municipality of Aker took over the common stock, though the preferred stock remained listed on the Oslo Stock Exchange until 1975, as Oslo Sporveier gradually took over the operation of the western suburban lines. Akersbanerne opened the connecting Sognsvann Line in 1934. Metro The first idea to launch a citywide rapid transit was launched in 1912 with the construction of the Ekeberg Line; constructed with the same width profile as the Holmenkollen Line, the plan was to build a tunnel under the city center and run through trains, but large cost expenditures on the first section of the Common Tunnel ceased the plans. As part of the rebuilding after World War II a planning office for a T-bane was established in 1949, with the first plans launched in 1951; in 1954, the city council decided to build the T-bane network in Eastern Oslo with four branches. The system would feature improvements over the suburban lines in having a third rail power supply, cab signaling with Automatic Train Protection, stations long enough for six-car trains and level crossings replaced by bridges and underpasses—specifications christened metro standard. At the time there were two suburban tramways on the east side, the Ekeberg Line (opened in 1919) and the Østensjø Line (1923). Only the latter would be connected to the T-bane; the Ekeberg Line would remain a tramway, but three new