Norway is currently constructing Rogfast, a record-breaking undersea road tunnel that, once completed, will stretch 27 kilometers and reach a depth of 392 meters below sea level. Set to become the world’s longest and deepest undersea tunnel for road traffic, Rogfast is a cornerstone of Norway’s vision to eliminate ferry crossings along the E39 coastal highway.
The construction began in 2018 but faced early obstacles, including a temporary suspension due to projected cost overruns. Work resumed in 2021 after restructuring, and completion is now expected in 2033. With an estimated cost of 25 billion Norwegian kroner, or around $2.4 billion, Rogfast stands as one of the most technically demanding infrastructure projects in Europe.
Precision and Pressure Under the Seabed
To build a passageway of this scale under the sea, engineers are digging from both ends, aiming to meet in the middle with a margin of error under 5 centimeters. This level of precision demands state-of-the-art technology. As reported by CNN, laser scanners are used to collect 2 million data points per second, generating a digital twin of the underground route that can be continuously compared against design specs.
Burkhard Boeckem, Chief Technology Officer at Hexagon, the company responsible for these measurements, emphasized the stakes:
“If you deviate from this, you create so much more material that needs to be taken out, and then so much more to be filled in again, it’s a lot of whole trucks.”
This massive infrastructure effort is intended to shorten travel times, improve safety, and support regional economic development across some of the country’s most isolated areas.
A New Undersea Giant
The Seikan Tunnel, built for rail traffic, reaches 240 meters below sea level, while the rail-only Channel Tunnel bottoms out at 115 meters. Rogfast is designed to go deeper than both, with a planned maximum depth of 392 meters, making it the deepest undersea road tunnel ever attempted.
As reported by CNN, the tunnel will feature two separate tubes, each with two traffic lanes, and even includes a double roundabout located 260 meters below sea level. This design element links to a connection tunnel to Kvitsøy, Norway’s smallest municipality.
Undersea Tunnel Engineering
One of the major technical issues has been sealing the rock to prevent seawater intrusion. As Anne Brit Moen, project manager at Skanska, told CNN:
“We are now 300 meters (984 feet) below sea level, and we have already had quite extensive saltwater leaks in the tunnel system.”
Maintaining air quality in the 27-kilometer tunnel is a key challenge. A longitudinal ventilation system, supported by shafts to Kvitsøy, will be used alongside real-time alerts, radar, and surveillance for safety. According to Moen, beyond the physical tunnel, the project is expected to bring longer-term benefits to local communities.
“The project also creates substantial employment during construction and lays the groundwork for more sustainable and integrated regional development,” she said.
By replacing ferries, it will strengthen access to jobs, public services, and education and lower logistics costs for industries such as seafood.
Norway is Digging the World’s Deepest Road Tunnel, 400 Meters Under the Sea
