The line runs parallel to Ring 3, through four stations in Oslo: Montebello, Ullernåsen, Åsjordet and Bjørnsletta.

[3] Situated 11.4 kilometers (7.1 mi) from Stortinget,[4] Bekkestua is the terminal station for the tramway, and a major transit hub for central Bærum.

It runs along the Røa Line from Smestad to Majorstuen and onwards in the Common Tunnel through the city center.

[5] Operations are carried out by Sporveien T-banen on contract with Ruter, the public transport authority in Oslo and Akershus.

[8] Bærum grew as a suburb of Oslo after the Drammen Line of the Norwegian State Railways opened through the southern part of the municipality in 1872.

Local investors applied in 1897 to establish a tramway that would run parallel to the Drammen Line from Oslo to Sandvika—which at the time was steam-hauled, narrow gauge and single tracked and suffered from low regularity.

Instead, the state started to modernize the Drammen Line by converting it to standard gauge, electrifying it and building double track.

An agreement was quickly reached with Kristiania Elektriske Sporvei (KES), the owner of the Lilleaker Line.

The municipal council voted in favor of the southern line in 1921 after first rejecting a proposal to negotiate trackage rights with Holmenkolbanen.

The main argument for the southern alternative was that the municipality would not have to pay any of the investment costs for the section of the line that would be localed within Aker.

Passengers carried out a strike in 1924; this resulted is slightly cheaper tickets, but at the same time the trams and stations were equipped with advertisements.

The free land for the extension was only valid for a limited time, and to be able to construct the line before the deadline, a single-track solution was chosen.

Concession for this route was granted on 30 April 1937, but Aker Municipality protested, because they did not want noise pollution at the hospitals.

The work also involved widening the profile between Jar and Egne hjem so the Class C could operate on the whole length of the line.

In addition, two Class A trams were converted to the wider and longer Class D.[9] With the opening of the connection, the 16.4-kilometer (10.2 mi) section from Sørbyhaugen to Kolsås was designated the Kolsås Line, and the 3.8-kilometer (2.4 mi) section from Jar to Skøyen was designated as the Lilleaker Line.

A balloon loop was built at Jar, allowing the new Class B trams that served the Lilleaker Line to turn there.

The T6 series of fifteen units were built with a driver's cab at both ends, so single-car trains could be operated in the evenings.

The upgrade involved the line receiving automatic train control with cab signaling, third-rail power supply and longer platforms.

After the Røa Line reopened, the third rail had been laid to Montebello, and the trains had to switch power supply and signaling system there.

[9] Budgetary disagreements between local politicians in Oslo, Bærum and Akershus led to the closure of the Bekkestua to Kolsås leg on 1 July 2003.

The first proposal came in 2002, when it was stated that the metro should terminate at Lysakerelven and that the rest of the line be operated as part of the tramway.

The first three upgraded stations, Montebello, Ullernåsen and Åsjordet, were put back into the service of Line 6 from 18 August.

The upgrades were similar to those to the Røa Line in 1995, including installation of third rail, straight platforms long enough for six-car trains, a new signaling system as well as all-new permanent way and stations.

[10] In addition to a general increase in construction costs, a major calculation error had been carried out based on estimates for a light rail, rather than a rapid transit.

[13] An audit in 2010 concluded that the planning had been based on lack of reviews and risk management, with best-case estimates being used instead of properly risk-adjusted ones.

[10] Bærum Municipal Council rejected a proposition in 2010 to build additional housing in the vicinity of the metro stations.

Travel time from Kolsås to Rykkinn is estimated at 4 minutes along a 2.6-kilometer (1.6 mi) line, largely in tunnel.

The tramway is pursuing a shelfware tram mode which has low investment costs and optimized for street running.

If the trams are to be used concurrently with the metro, they need to have a reinforced cab to better withstand a head-on collision and automatic train protection.

This will make procuring shelfware impossible, while providing worse sight-lines for the motorman and increased damage in case of collisions elsewhere.