Norway Is Building the World’s Longest Undersea Road Tunnel: 27 Kilometers Long and 400 Meters Below Sea Level

An undersea tunnel promises faster travel and steadier lives along Norway’s stormy west coast.

For generations, Norway’s west coast has lived by ferry timetables and weather forecasts. A strong wind could stretch a routine commute into an all-day affair. A winter storm could reroute ferries entirely, leaving trucks, workers, and tourists waiting at the water’s edge.

Now the country is trying something different. Deep beneath the sea, engineers are carving a huge tunnel through solid rock, aiming to make weather irrelevant.

The project is called Rogfast, short for Rogaland fastforbindelse, or “fixed link.” When completed, it will become the world’s longest and deepest undersea road tunnel. Stretching roughly 27 kilometers (about 17 miles) and plunging nearly 400 meters (1,312 feet) below sea level, Rogfast is designed to replace a key ferry crossing on the E39 coastal highway.

That highway runs for about 1,100 kilometers from Trondheim in the north to Kristiansand in the south. Today, the journey takes around 21 hours and requires seven ferry crossings. Rogfast alone will remove one of the longest and most vulnerable gaps, cutting about 40 minutes from travel between Stavanger and Bergen, Norway’s fourth- and second-largest cities. The project is supposed to be completed in 2033.

“The tunnel will significantly improve connectivity along the Norwegian west coast, by creating a faster and more reliable link between the Stavanger and Haugesund regions,” said Anne Brit Moen, a project manager at Skanska, the multinational construction company that’s building the northern part of the tunnel, in comments reported by CNN.

The End of a Ferry Bottleneck

Rogfast links the districts of Randaberg and Bokn, separated by more than 26 kilometers of open water. Today, ferries do the work. It’s not so bad, but during the winter season, you’ll see many vehicles queuing.

“The port at Mortavika is quite exposed and, in the winter, ferries sometimes have to divert to another port,” Oddvar Kaarmo, the project manager at the Norwegian Public Roads Administration, told The Telegraph. “Once the tunnel is finished, we will not have to rely on good weather to keep the roads open.”

The tunnel will consist of two parallel tubes, each carrying two lanes of traffic. At its deepest point, the road will lie about 390 meters below sea level, embedded in bedrock rather than resting on the seabed.

Norway favors this approach. Unlike projects such as the Fehmarn Belt link between Germany and Denmark, which uses prefabricated sections laid into trenches, Rogfast is drilled and blasted directly through rock. “You are travelling through solid rock,” Kaarmo told Euronews. “Our regulations demand 50 meters” of rock between the tunnel and the sea.

Midway through the tunnel, traffic will encounter one of its most unusual features. Beneath the island of Kvitsøy, Norway’s smallest municipality, two roundabouts are being carved 260 meters underground. They connect the island to the main tunnel and allow traffic to keep moving even if part of the system closes.

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“As far as I know, I haven’t seen two roundabouts in a cross-section area in a tunnel before,” Kaarmo added.

Precision at 400 Meters Deep

So far below the sea, precision matters more than speed. Crews are working from both ends at once, aiming to meet in the middle with an error margin of just five centimeters. To manage that, engineers rely on lasers and digital mapping. Scanners measure freshly excavated rock, capturing millions of data points per second to create a “digital twin” of the tunnel. Engineers can correct deviations early, before they become costly.

“It’s a little bit away from the romantic view of the surveyor looking through an eyepiece,” said Burkhard Boeckem, chief technology officer at Hexagon, the measurement firm involved, told CNN.

Depth brings other problems. Water pressure increases the risk of leaks, and saltwater has already forced engineers to refine how they seal the rock. “We have already had quite extensive saltwater leaks in the tunnel system,” Moen added, as crews push toward the deepest sections.

The design includes built-in safety systems. Cross-passages link the two tubes. Cameras, radar, and real-time alerts will monitor traffic. Ventilation fans and vertical shafts will manage air quality along the tunnel’s length. The project costs about 25 billion Norwegian kroner, roughly €2 billion. The government will pay around 40%, with the rest covered by tolls.

Beyond engineering, the tunnel reflects a broader ambition. By building Rogfast, Norway is pushing forward its long-term effort to make the E39 ferry-free, a task expected to last until about 2050. The Rogfast tunnel itself is slated for completion in 2033. Supporters argue it will lower transport costs, strengthen the seafood industry, and make daily commuting more predictable.