The Romerike Tunnel () is a railway tunnel in Norway between Oslo and Lillestrøm. It is the second longest railway tunnel in Norway after the Blix Tunnel opened in 2022, and forms the first section of the Gardermoen Line. It is double track and electrified, permitting speeds of . Construction started in 1994, with plans to open with the rest of the Gardermoen Line and Oslo Airport, Gardermoen on 8 October 1998. Due to serious leakage from Lutvann and several other lakes, it did not open until 22 August 1999. The leaks increased the cost of the tunnel from to NOK 1.8 billion. The main contractor was Scandinavian Rock Group. The tunnel was originally owned by NSB Gardermobanen, then the Norwegian National Rail Administration, and now owned by Bane NOR. 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. Background The tunnel was constructed as part of the high-speed Gardermoen Line which runs from Oslo to Eidsvoll via Oslo Airport, Gardermoen. The tunnel makes up most of the section between Oslo Central Station and Lillestrøm Station and was built to bypass the meandering Trunk Line which dates from 1854. 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. The Romerike Tunnel would also be straighter and allow higher through speeds, decreasing travel time from 29 to 12 minutes. The decision to build the Gardermoen Line and Romerike Tunnel was taken by the Norwegian Parliament on 8 October 1992, with the opening planned for six years later on 8 October 1998. An alternative airport site to Gardermoen was proposed at Hurum, south-west of Oslo. 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. The tunnel is used by all trains on the Gardermoen Line, including the Flytoget airport express, and the regional and express trains which continue via the Dovre Line. Local trains on the Hoved Line and Kongsvinger Line to the north also use the tunnel. Use of the Hoved Line is limited to freight trains and commuter trains which make stops along the route. Construction Construction started in