The Grorud Line was built as part of the original metro network and opened on 16 November 1966.
The Ring Line was built in two stages between 2000 and 2006.
Oslo Sporveier announced in 2005 that it planned to double the number of services on the Grorud Line, to eight per hour.
However, the bottleneck of the system is the Common Tunnel through the city center and services on all branches of the metro are limited by the capacity of that line.
With the Ring Line under way, planners started to look at how it could be used to increase traffic flow and capacity of the metro.
This would allow traffic to be diverted around the Ring Line instead of through the Common Tunnel, increasing capacity on the system as a whole.

Five alternatives were proposed in 2007, which considered various ways to connect the Grorud Line and the Ring Line.
Variations included building part of the line with single track and whether or not to construct a station at Løren.
The latter would increase the price, but would give the area a significantly better transit service.
As of 2007 the area was only served by a bus every twenty minutes.
Funding of the Løren Line was secured as part of Oslo Package 3.
During planning the line was variously known as the Løren Curve (Lørensvingen) and the Hastle Curve (Haslesvingen).

An alternative or supplemental proposals has been to use the Alna Line as a cross-town services of the Oslo Commuter Rail.
Both the Norwegian National Rail Administration and Ruter have investigated the possibility to run services from the Trunk Line across the Alna Line and up the Gjøvik Line, but have found a too low traffic potential to carry out the proposal.

The Løren Line is being built at the same time as the Løren, Hasle and Økern area is undergoing a major redevelopment.
While the area previously has had some residential areas and has mostly been dominated by industry, it has now been designated a primary site for urban development in Oslo.
The area has a potential for 25,000 residences and 2.5 million square meters (25 million sq ft) of commercial area.
Oslo Municipal Council approved in May 2013 the construction of 730 apartments in the immediate vicinity of the station.

Planning of the Løren Line is part of a wider concept of building additional rail-based services across Groruddalen.
There are three lines, two metro lines and the mainline Trunk Line, which run down the valley, but there is no good system for crossing the valley.
This is in part caused by both railways and motorways creating barriers.
The municipal authorities are therefore looking at future connections between the metro's Grorud Line and the Furuset Line, with a possible transfer station with the Trunk Line.

The zoning plan allow the line was passed on 14 December 2011.

The contract for the ground work of the line was awarded by Sporveien to Skanska on 13 May 2013 and had a value of 357 million Norwegian krone and construction commenced in June.
The project also included upgrade of the stations Rommen, Romsås and Vestli on the Grorud Line.
The lower parts of the Grorud Line was closed from September through December to allow construction work on the connection.
The Ring Line from Sinsen to Carl Berners plass is similarly proposed closed from June 2014 to March 2015.
Construction is scheduled for completion in October 2015 and to be opened in early 2016.
Construction was carried out with two crossections, from Anders Winsvoldsvei and Båhusveien at Bilia.
In addition, Løres Station was built with the cut-and-cover method, doubling as a crossection.

The line opened on 3 April 2016.
The Grorud Line was built as part of the original metro network and opened on 16 November 1966. The Ring Line was built in two stages between 2000 and 2006. Oslo Sporveier announced in 2005 that it planned to double the number of services on the Grorud Line, to eight per hour. However, the bottleneck of the system is the Common Tunnel through the city center and services on all branches of the metro are limited by the capacity of that line. With the Ring Line under way, planners started to look at how it could be used to increase traffic flow and capacity of the metro. This would allow traffic to be diverted around the Ring Line instead of through the Common Tunnel, increasing capacity on the system as a whole.
Five alternatives were proposed in 2007, which considered various ways to connect the Grorud Line and the Ring Line. Variations included building part of the line with single track and whether or not to construct a station at Løren. The latter would increase the price, but would give the area a significantly better transit service. As of 2007 the area was only served by a bus every twenty minutes. Funding of the Løren Line was secured as part of Oslo Package 3. During planning the line was variously known as the Løren Curve (Lørensvingen) and the Hastle Curve (Haslesvingen).
An alternative or supplemental proposals has been to use the Alna Line as a cross-town services of the Oslo Commuter Rail. Both the Norwegian National Rail Administration and Ruter have investigated the possibility to run services from the Trunk Line across the Alna Line and up the Gjøvik Line, but have found a too low traffic potential to carry out the proposal.
The Løren Line is being built at the same time as the Løren, Hasle and Økern area is undergoing a major redevelopment. While the area previously has had some residential areas and has mostly been dominated by industry, it has now been designated a primary site for urban development in Oslo. The area has a potential for 25,000 residences and 2.5 million square meters (25 million sq ft) of commercial area. Oslo Municipal Council approved in May 2013 the construction of 730 apartments in the immediate vicinity of the station.
Planning of the Løren Line is part of a wider concept of building additional rail-based services across Groruddalen. There are three lines, two metro lines and the mainline Trunk Line, which run down the valley, but there is no good system for crossing the valley. This is in part caused by both railways and motorways creating barriers. The municipal authorities are therefore looking at future connections between the metro's Grorud Line and the Furuset Line, with a possible transfer station with the Trunk Line.
The zoning plan allow the line was passed on 14 December 2011.
The contract for the ground work of the line was awarded by Sporveien to Skanska on 13 May 2013 and had a value of 357 million Norwegian krone and construction commenced in June. The project also included upgrade of the stations Rommen, Romsås and Vestli on the Grorud Line. The lower parts of the Grorud Line was closed from September through December to allow construction work on the connection. The Ring Line from Sinsen to Carl Berners plass is similarly proposed closed from June 2014 to March 2015. Construction is scheduled for completion in October 2015 and to be opened in early 2016. Construction was carried out with two crossections, from Anders Winsvoldsvei and Båhusveien at Bilia. In addition, Løres Station was built with the cut-and-cover method, doubling as a crossection. 
The line opened on 3 April 2016.
Løren Line