The Sognsvann Line is a rapid transit line on the Oslo Metro of Norway. It branches from the Common Tunnel at Majorstuen and runs 6.0 kilometers (3.7 mi) to Sognsvann. After Ullevål stadion, the Ring Line branches off. The Sognsvann Line serves the northwestern and northern neighborhoods of Oslo, mostly within the borough of Nordre Aker. The line is owned and maintained by Kollektivtransportproduksjon and has nine stations. The western end of line 5 serves the entire line. Line 4 and the eastern end of line 5 serve the southern part of the line up to Ullevål stadion before branching off and continuing along the Ring Line. This gives an average five-minute headway on the southern part and an average fifteen-minute headway on the northern part of the line.

The Oslo Metro 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 85 kilometres (53 mi), 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 neighbouring municipality of Bærum. In 2016, the system had an annual ridership of 118 million.