page_title: Common Tunnel
section_title: The gap
hierarchical_section_title: Common Tunnel / History / The gap
caption_attribution_description: Stortinget station on the Oslo T-bane, Norway
context_page_description: The Common Tunnel, sometimes called the Common Line, is a 7.3-kilometer long tunnel of the Oslo Metro which runs through the city center of Oslo, Norway. The name derives from the fact that all six lines of the metro use the tunnel, which runs from Majorstuen to Tøyen. The section has six stations, including the four busiest on the metro.
  The tunnel was first built as two separate tunnels which were later connected. The Holmenkolbanen company opened the western section of the tunnel from Majorstuen via Valkyrie plass to Nationaltheatret in 1928. In 1966, the Oslo Metro opened, including the tunnel from Tøyen via Grønland to Jernbanetorget. In 1977, the eastern end was extended to Sentrum, but the extension was closed in 1983 because of water leakages. In 1987, the Sentrum station reopened as Stortinget, and became the terminus of both the western and eastern lines. By 1993, the western end had been upgraded to metro standard, Valkyrie plass was closed, and the first trains ran through the whole tunnel.
  The section from Tøyen to Brynseng, although not completely located within the tunnel, is considered part of the Common Line.
context_section_description: During the 1960s, the Drammen Line was being planned to connect to Oslo East Station through the proposed Oslo Tunnel. This would make Oslo West Station unnecessary, and would allow a central station to be built at the location of the East Station. The railway tunnel was planned with an intermediate railway station at Nationaltheatret. Simultaneously, Oslo Sporveier worked on possibilities to connect their eastern and western networks, and extend both to the city core. During the 1960s, the planning office for the metro proposed a tunnel between Nationaltheatret and Jernbanetorget, which would run parallel to the Oslo Tunnel. The initial plans called for a station at Slottsparken, close to Nationaltheatret, which would serve as the transfer point between the metro and the western light rail. This station was designed to handle 25,000 people per day.
  At the time, the western and eastern networks were incompatible; in addition to different platform heights, the eastern network used six-car trains with a third-rail power supply, while the western network used overhead wires and two-car trains. The initial plans were met with criticism, following the media's discovery that the main planners had not consulted several hired specialists, and that alternatives to the preferred route had not been considered. As a consequence, several engineers working for NSB made two alternative suggestions for the route. By 1975, the plans were changed so that Nationaltheatret would become the transfer station, by building a balloon loop for the metro, while allowing the western trains to terminate as before. This solution would allow the two networks to be connected later.
  The decision to build Sentrum Station, located 700 meters (2,300 ft) west of Jernbanetorget, was taken by the city council on 22 May 1969. The decision also involved the transfer station being placed at Slottsparken/Nationaltheatret. Construction of Sentrum started in 1972, and was immediately followed by the first water leaks being discovered. By the time the station opened on 9 January 1977, there were still no adequate countermeasures for the leaks. During trials in January, it was discovered that the tracks were too low to allow all types of trains to open their doors, resulting in the tracks having to be raised. In 1978, the city planner discarded the proposal by Oslo Sporveier to build a new station at Slottsparken, and instead decided that Sentrum would become the interchange between the two systems. This would allow the western network to be upgraded to metro standard at a later date, and subsequently also allow metro trains to run through the center. The proposal was supported by all political parties except the Labour Party.
  By 1978, the contractor and the municipality felt that the leaks were under control, and the municipality took over the station. On 20 February 1983, the station was closed for renovation to remove the leaks. At the time, it was expected that the station could reopen in 1984. The cause of the leaks was a combination of the wrong type of concrete being used and the wrong construction method. These were specified correctly in the tender contracts, but after the contractor was chosen, an agreement was made between the municipality and Selmer for the use of the membrane method. Combined with the inferior quality of concrete, the leaks were unavoidable. In 1986, the municipality sued Selmer for the NOK 158 million it cost to repair the station.
  The station reopened on 7 March 1987, and took the name Stortinget, which derives from the Parliament of Norway Building (Norwegian: Stortinget), which is adjacent to the station. Trains from the western network terminated at the old platforms, where the metro had previously terminated. The metro trains instead ran through a balloon loop. The station featured a 40-meter (130 ft) step-free walk between the two systems. With the opening of Stortinget, the metro network was declared finished, after the last extension on the Furuset Line to Ellingsrudåsen had been made in 1981.
  On 7 October 1987, the city council
caption: Stortinget
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