Four-fifths of the line runs within two tunnels, with the 1.0-kilometer (0.62 mi) section between Storo and Sinsen, including both stations, being the only at-grade part.

Nydalen and Storo are such located that trains in either direction use the same time along the loop, effectively giving a five-minute headway to the city centre.

By the 1960s, Oslo had a rapid transit network that branched out north-east and north-west from the city centre.

[2] Oslo Sporveier, the contemporary operator of the metro, started planning the line during the late 1980s.

[4] A projection for the line was presented in 1991 by Oslo Sporveier, where daily ridership was estimated to be 54,000 passengers.

[6] When the operating company ordered new T2000 trains for the Holmenkoll Line, the design allowed future versions to have dual current systems, to handle both the 750 volts on the metro network (from a third rail and overhead wire), and the 15 kV  16.7 Hz AC system of the main railways.

[7] The new T2ds were seen as a preparation for the Ring Line, and were optimised for higher speeds than the old stock, being capable of operating at 100 kilometres per hour (62 mph).

[8] In 1992, the tram division of Oslo Sporveier launched an alternative Ring Line that would have been built as a light rail, using in part the existing tramway.

[9] Between 1994 and 1998, there was local political debate about how Rikshospitalet, that was moving to Gaustad, should be served by public transport.

[10] In 1998, an agreement was reached whereby the light rail line would be built, and a new station for transfer from the metro would open at Forskningsparken.

Many neighbours to the route of the Sognsvann Line complained about this proposal, stating that they had hoped that the section from Majorstuen to Berg would have been rebuilt as a tunnel.

Both Minister of Transport and Communications, Dag Jostein Fjærvoll from the Christian Democratic Party and Oslo City Commissioner of Transport and the Environment, Merete Agerbak-Jensen from the Conservative Party, agreed upon the distribution of funding from the city and state, and both wanted construction to start as soon as possible.

[17] The first section opened from Ullevål stadion via Nydalen to Storo on 20 August 2003,[18] costing NOK 590 million.

[19] Nydalen had grown up as an urban redevelopment area after the local industry had been abandoned in the 1980s,[18] where 14,800 jobs had been located by 2004.

[18] On 20 August 2006, the final section opened, from Storo via Sinsen to Carl Berners plass,[20] with the whole project costing NOK 1,348 million.

A survey conducted by the city in 2003 and 2007 showed that the Ring Line had a significant impact on the use of public transport in the area.

From Storo to Sinsen, the tracks are laid parallel to the Gjøvik Line of the mainland railway.

Also the Sinsen Line of the Oslo Tramway and the Ring 3 motorway follow the same corridor between the two stations.

The escalators leading down to the platform features The Tunnel of Light, an artistic presentation of sound and colour around the passengers as they ascend from or to descend to the station.

If running clockwise, they pass through all the common stations (Tøyen, Grønland, Jernbanetorget, Stortinget, Nationaltheatret and Majorstuen).

They head north on the Sognsvann Line, stopping at Blindern, Forskningsparken and Ullevål stadion.

Transfer to Oslo Central Station, which serves all trains in Eastern Norway, is available at Jernbanetorget.