The Oslo Metro ( or or simply ) is the rapid transit system of Oslo, Norway, operated by Sporveien T-banen on contract from the transit authority Ruter. The network consists of five lines that all run through the city centre, with a total length of , serving 101 stations of which 17 are underground or indoors. In addition to serving 14 out of the 15 boroughs of Oslo, two lines run to Kolsås and Østerås, in the neighboring municipality of Bærum. In 2016, the system had an annual ridership of 118 million. The first rapid transit line, the Holmenkollen Line, opened in 1898, with the branch Røa Line opening in 1912. It became the first Nordic underground rapid transit system in 1928, when the underground line to Nationaltheatret was opened. After 1993 trains ran under the city between the eastern and western networks in the Common Tunnel, followed by the 2006 opening of the Ring Line. All the trains are operated with MX3000 stock. These replaced the older T1000 stock between 2006 and 2010. History Suburban lines in the west Rail transport in Oslo started in 1854, with the opening of Hoved Line to Eidsvoll, through Groruddalen. In 1872, Drammen Line, going through Oslo West, and in 1879, Østfold Line going through Nordstrand opened, offering a limited rail service to those parts of the city. By 1875, Kristiania Sporveisselskab (KSS) opened the first horsecar trams. In 1894 electric trams were in service by Kristiania Elektriske Sporvei (KES). The first suburban tram line was the Holmenkollen Line that was opened by Holmenkolbanen in 1898; like all the later suburban tram line these were electric trams with a grade-separated right-of-way and proper stations instead of tram stops, making it the first rapid transit in Oslo. Unlike the other suburban tram lines that were built later, the Holmenkollen Line was not extended into the city as a streetcar—instead passengers had to change at Majorstuen to the streetcars, though the system did not take into use wider suburban stock () until 1909. A branch line was opened in 1912, to Smestad, and in 1916 the Holmenkollen Line was extended to Tryvann, with the last part from Frognerseteren single track and used for freight, and removed in 1939. In 1912, the construction of the first underground railway in the Nordic Countries started, when A/S Holmenkolbanen started construction of an extension of their line from Majorstuen