Common Tunnel

The Common Tunnel (Norwegian: Fellestunnelen), sometimes called the Common Line (Fellesstrekningen), is a 7.3-kilometer (4.5 mi) 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. At Majorstuen, the line splits into three; the Røa Line, the Holmenkollen Line and the Sognsvann Line. At Tøyen, the line splits into the Lambertseter Line and the Grorud Line. The tunnel is the bottleneck of the metro, allowing 24 trains per hour in each direction west of Stortinget, and 28 east of Stortinget.