The Oslo Metro is the rapid transit system of Oslo, Norway, operated by Oslo T-banedrift on contract from the transit authority Ruter. The network consists of six lines that all run through the city center, with a total length of 84.2 kilometres (52.3 mi). It has a daily ridership of 200,000 with 105 stations of which 16 are underground or indoors. In addition to serving all 15 boroughs of Oslo, two lines run to Bærum. The first rapid transit line was the Holmenkoll Line, opened in 1898, with the branch Røa Line opening in 1912. It became the first Nordic underground railway in 1928 when the underground line to Nationaltheatret was opened. The Sognsvann Line opened in 1934 and the Kolsås Line in 1942. The opening of the upgraded T-bane system on the east side of town occurred in 1966, after the conversion of the 1957 Østensjø Line, followed by the new Lambertseter Line, the Grorud Line and the Furuset Line; in 1993 trains ran under the city between the two networks in the Common Tunnel, followed by the 2006 opening of the Ring Line. Between 2006 and 2010 the system is replacing the older T1000 stock with MX3000 stock. (Full article...)