Tanum Tunnel

The cost to build the tunnel, excluding the superstructure, was 370 million Norwegian krone (NOK).

The tunnel runs mostly through Cambrian-Silurian sedimentary slate, nodular limestone and shale, with local occurrences of Permian igneous rock.

[4] At Åstad, the line runs 600 meters (2,000 ft) in the open before entering the Skaugum Tunnel.

[3] The line is electrified at 15 kV  16.7 Hz AC and allows a maximum speed of 160 kilometres per hour (100 mph).

The line was built to allow increased railway traffic though the main corridor west of Oslo.

Previously, the only railway west of Oslo was the Drammen Line, which has limited capacity and is used by a mix of local, regional, intercity and freight trains.

The tunneling cost NOK 370 million, including the open section between Solstad and Åstad, but excluding superstructure.

The main part of the tunnel was built using the drilling and blasting method, using two points of entry.

In March 2004, a test was done in the tunnel to insure that the requirements would be met, as low-frequency sound is difficult to predict.

The National Rail Administration has stated that savings made to the specifications in the water and frost methods have caused higher maintenance costs because the small leaks which are present do a lot of harm.