Norway’s geography presents unique challenges for drivers. With over 1,100 fjords—deep glacial inlets that separate land masses—traveling from one place to another often involves numerous detours, multiple bridges, and even ferry crossings. In June 1992, the Norwegian Parliament approved the construction of what would become the world’s longest road tunnel. This 24.5 km tunnel links Aurland and Laerdal along the new main highway between Oslo and Bergen, providing a solution for a region previously hindered by unreliable road transport due to its mountainous terrain, narrow roads, and frequent fjord crossings.

Laerdal Tunnel

The structure is officially called a submerged floating tube-bridge but is also known as a Archimedes Bridge.

3D view of the Laerdal Tunnel

3D view of the submerged floating tunnel

The construction of the Laerdal Tunnel was carried out in four main phases: drilling, blasting, loading and transport, and excavation with landscaping.
Drilling was performed using computer-controlled drilling jumbos alongside traditional drilling and blasting methods. To ensure that the tunnel sections could meet more than 10 km inside solid rock and 1,000 meters beneath the mountain, high precision was essential.
Satellite navigation was used to establish fixed survey points, serving as reference coordinates for measurements inside the tunnel. Within the tunnel, direction was indicated using laser beams, which were detected by the drilling jumbo’s onboard computer to automatically position the drilling equipment according to a predefined pattern. Each drilling jumbo was equipped with three automatic hydraulic drills.

Blasting involved drilling approximately 100 holes, each 45–51 mm in diameter and 5.2 meters deep, for every blasting cycle. A detonator, placed inside a small stick of Anolit dynamite, was positioned at the base of each hole.

For loading and transport, wheel-mounted loaders were deployed, and excavated material was removed using dump trucks. A permanent road was constructed inside the tunnel in parallel with excavation works, allowing transport vehicles to operate on a well-paved surface during construction. This approach improved efficiency and reduced pollution.

The tunnel features a longitudinal ventilation system with a single air exhaust shaft located 18 km from the Aurland entrance. About 10 km from the same entrance, a side tunnel houses an air-cleaning plant, designed to filter critical pollutants from the ventilation airflow. This system ensures acceptable air quality throughout the tunnel during heavy traffic and reduces both the volume of air and the power required for ventilation in the long tunnel.

References
Dhar, B. (n.d.). Technological innovations: Road tunnel in Norway. Ex-World Bank & UN.
Norstroem, E. (2006, March 10). Basic installations to provide safe operation for low traffic tunnels. Norwegian Public Roads Administration.