The tunnel was built by Mika for the Norwegian National Rail Administration using the drilling and blasting method with one crosscut.

The cost to build the tunnel, excluding the infrastructure, was 450 million Norwegian krone (NOK).

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

[3][4][5] The line is electrified at 15 kV  16.7 Hz AC and allows for maximum speeds of 160 kilometers per hour (99 mph).

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

[11] The tunnel was built using the drilling and blasting method using two points of entry, the entrance on the Asker side and from a crosscut at Skaugum.

Construction involved blasting 450,000 cubic meters (16,000,000 cu ft) of earthwork and drilling 275 kilometers (171 mi) of holes for pre-injection.

The Norwegian Labour Inspection Authority criticized Mika for improper safety routines and required them to improve them, but concluded that no criminal offenses had been committed.

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 by the specifications in the water and frost protection methods have caused high maintenance costs because the small leaks which are present have done a lot of harm.