The line also serves the mostly residential boroughs of Bøler and Østensjø.
The plans would lead to the system opening in 1966, after the conversion of the Østensjø and the Lambertseter Line of the Oslo Tramway to metro standard, and supplemented with the new Furuset and Grorud Line.
In 1937, the first Class B trams were delivered to Oslo Sporveier, and these put into service on the Bærum–Østensjø Line after the serial delivery started in 1939.