27 kilometers long and 400 meters deep: European country is building the world’s longest underwater road

Norway is building the world’s longest and deepest undersea road link.

The Rogfast tunnel will both improve travel time between the major cities and be part of a new ferry-free highway along the west coast of Norway.

Construction of the Rogfast tunnel, also known as the Boknafjord tunnel, is in full swing in Western Norway.

The tunnel will connect Randaberg north of Stavanger with Bokn municipality.

The total tunnel construction will consist of two separate runs, with two lanes in each direction.

The total length will be 27 kilometers, surpassing the current record holder, the Lærdal tunnel, which is also located in Norway and measures around 24.5 kilometers.

Work started in January 2018, but was temporarily halted in 2019 due to expected budget overruns.

This led to the cancellation of contracts and a restructuring of the project.

Construction resumed at the end of 2021 and is now expected to be completed in 2033.

The total cost is estimated at NOK 25 billion, approximately DKK 15.65 billion.

Double roundabout and high precision

One of the most remarkable details of Rogfast is that the tunnel will also provide access to Kvitsøy.

This is done via a double roundabout built 260 meters below sea level.

This is a construction that has not previously been seen on this scale in underwater projects.

At its deepest point, the tunnel will be around 392 meters below sea level.

This presents technical challenges, including the extreme water pressure of up to 40 bar.

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According to project manager Anne Brit Moen at contractor Skanska, saltwater intrusion has already been experienced during construction, even before the tunnel reached a depth of 300 meters.

The tunnel is being built simultaneously from both ends, and the ambition is for the two parts to meet with an accuracy of just five centimeters.

This requires sophisticated measuring equipment, including laser scanners that record up to two million data points per second to create a digital twin of the tunnel tube.

Part of an extensive infrastructure project

The Rogfast project is a key part of the modernization of the E39, which stretches over 1,100 kilometers from Trondheim to Kristiansand.

Today, this journey takes around 21 hours and involves seven ferry crossings.

The overall project will make the entire stretch ferry-free and reduce travel time to around 11 hours.

In addition to improving accessibility between cities, the project will also strengthen connections between smaller island communities and the Norwegian mainland.

The tunnel will be equipped with a longitudinal ventilation system supplemented with ventilation shafts to Kvitsøy.

In addition, camera and radar surveillance will be introduced, as well as real-time alerts in the event of traffic jams or accidents.

These technological solutions will ensure safety and efficient air circulation along the entire length of the tunnel.

Although ferry operations will be reduced, the authorities expect Rogfast to make a positive contribution to the local economy by facilitating access to jobs, educational institutions and public services.

Logistics costs for the fishing industry, for example, are also expected to fall significantly.

Norwegian authorities expect the Rogfast tunnel to be completed in 2033.

The overall upgrading of the E39 is expected to be completed around 2050.