Norway Building World’s Longest and Deepest Undersea Road Tunnel

Norway is constructing the world’s longest and deepest subsea road tunnel, a 27-kilometre project named Rogfast along the country’s western coast. Once completed, the tunnel will allow motorists to travel between cities without relying on ferries, reducing travel time between the major cities of Bergen and Stavanger by around 40 minutes.

The tunnel will reach a maximum depth of 392 metres (1,286 feet) below sea level. Construction began in January 2018 but was suspended towards the end of 2019 amid concerns over rising costs. Work resumed in late 2021 following a restructuring of the project.

The tunnel is now scheduled for completion in 2033, with an estimated cost of around 25 billion Norwegian kroner, equivalent to approximately $2.4 billion.

Ann Brit Moen, project manager at construction company Skanska, said the tunnel would significantly transform transport links along Norway’s western coast. It is expected to establish faster and more reliable connections between the Stavanger and Haugesund regions.

Rogfast will consist of two separate tunnel tubes, each featuring two lanes of traffic. Two roundabouts will be built at a depth of 260 metres below sea level, connecting the tunnel to Kvitsøy, Norway’s smallest municipality.

Advanced technology is being deployed to ensure precision during construction. Excavation is progressing simultaneously from both ends of the tunnel, with engineers aiming to keep the deviation between the two sections at the meeting point within just five centimetres.

Laser scanners are being used to collect two million data points per second. The information is then used to create a digital model of the tunnel, which is continuously compared with the original design.

One of the major engineering challenges is preventing seawater from seeping through layers of rock into the tunnel. Special ventilation systems will also be installed to ensure adequate airflow along the lengthy underground route. Cameras and radar systems will be used to detect accidents and monitor traffic conditions.

Rogfast is part of Norway’s wider 1,100-kilometre E39 Coastal Highway modernisation programme. Currently, travelling the entire route takes around 21 hours and requires motorists to cross seven ferry connections.

Through the construction of new roads, bridges and tunnels, Norway aims to reduce the journey time by approximately half. The overall E39 modernisation programme could continue until 2050.

Compared with Japan’s Seikan Tunnel and the Channel Tunnel beneath the English Channel, Rogfast will be constructed at a considerably greater depth below sea level. However, unlike those two rail tunnels, Rogfast is being designed exclusively for road traffic and is expected to become the world’s longest and deepest subsea road tunnel.