The tunnel allows long-distance, regional and Flytoget Airport Express Trains to bypass the old Hoved Line, reducing journey times between Oslo and Lillestrøm from 29 to 12 minutes.

Despite the older line being double track, capacity had reached its limit due to a combination of some trains making many stops and others none until Lillestrøm.

Had Hurum been chosen, the Gardermoen Line would not have been necessary for the airport express train, but the planning documents recommended that construction still proceed to ease traffic congestion north of Oslo.

[1] Construction started in August 1994, after a tender had been won by Scandinavian Rock Group (SRG), a collaboration between Målselv Anlegg, Nor Entreprenør and Peab.

[6] After the damage was discovered on 3 February 1997, legal actions were initiated by the Norwegian Water Resources and Energy Directorate requiring remedial measures to halt the leakage.

On investigation, Rhoca-Gil was revealed to contain a toxic substance called acrylamide, which caused health problems for the tunnel workers.

In addition, an extensive permanent pumping system was installed to restore and maintain lake levels in Østmarka.

[6] Curing the leaks and cleaning up the contamination delayed the tunnel's completion by a year, and it was finally opened on 22 August 1999.

An evaluation by the Ministry of Transport and Communications showed that NOK 500 million was spent fixing the leaks, but the report claimed that this was to a large extent a waste of money, resulting from inefficient engineering procedures.

After this diversion the express trains switched to the completed section of the new Gardermoen Line between Lillestrøm and Oslo Airport.