There is a megalophon tunnel to be built to forever change the map of Europe

On the banks of the Baltic Sea, in southern Denmark, it is taking shape a wide marvel of engineering – asking the giant piece of concrete – which, when completed, will dramatically redesign the road maps and rails in Europe.

Fehmanbelt’s tunnel may not have won the popular imagination in the same way as the Channel of the Channel, between Britain and France, for over 30 years, but this structure is equally impressive if not even more.

Calling Denmark and Germany, Fehmanbelt will have two lanes under the water in both directions, two more electrified raillines – one way of multiple tubes that will dive under the waves of one of the world’s busiest navigation routes.

At 18 kilometers, it is neither nearly as long as the 50 -kilometer stain channel tunnel, but in many other aspects is greater. The project will indeed be the longest road and rail tunnel in the world and the longest immersed tunnel in the world.

Being an “immersed” tunnel, instead of being excavated through a solid ground mass such as the spot canal tunnel, Fehmanbelt is built using prefabricated concrete sections that are thrown into a ditch at the bottom of the sea, connected together and then buried.

Last month, in February 2025, the first prefabricated sections of the tunnel, designated by elements, left the factory in Rødbyhavn, on the Danish side of the tunnel, completing the first part of an innovative Earth trip to the sea, which is scheduled for 2029.

The project of 7.4 billion euros is a gigantic venture in every way.

Each section of the tunnel is colossal. These concrete structures measure 217 meters long, 42 meters wide and nine meters deep, weighing a crushing 73,000 tons – the equivalent of 10 eiffel towers.

In total, 79 of these “normal” elements and 10 shorter “special” elements, 39 meters long (which will host the tunnel electrical installations), will be placed from end to end, from Rødbyhavn, on Lolland Island, to Puttgarden, on the German island of Fehmarn, creating the full tunnel up to 40 meters below the Baltic Sea.

To the proposal

Everything in the project is vast. The factory built for this purpose is the largest installation of tunnels in the world and, together with the work port, covers an area of ​​220 hectares – the size of over 300 soccer fields.

Three cavernous construction pavilions that contain six production lines (five for standard elements and one for special elements) are currently working 24 hours a day, producing an element of 217 meters every nine weeks.

Fused around dense reinforcement steel cages, each concrete element consists of nine 24 meter long segments. Once healed, the element is pushed to the upper basin, a large preparation area in front of the factory, where it is subjected to quality and equipment controls.

“We tried to install as much equipment as possible to be needed in the finished tunnel,” explains Denise Juchem, spokesman for Femern A/S, the Danish state company responsible for the project, to CNN.

“This saves time later and reduces logistics challenges for work in the immersed tunnel. In addition, monitoring equipment has been installed so that we can check the interior of the element at any time during transport and immersion.”

Ballast tanks are installed to ensure stability and steel foreclosure is fixed at each end of each section to make them watertight. This type of sealing allows the elements to float despite their huge tonnage.

The first fluctuation was successfully completed in early February, when the upper basin was isolated from the factory and slowly flooded with nearly 1 billion liters of seawater. Once floated, the element was towed to the lower basin, in preparation for your final trip to the tunnel ditch.

The date for the immersion of the first element has not yet been finalized, but the preparatory work is in full progress, says Juchem.

“This is a very complex process and also very dependent on weather conditions. We are currently testing the highly complex ships that have been specially built for our project.”

Complexity

“Ivy 1” and “Ivy 2” come in, the two immersion pontors whose function will be to ensure that each element is safely downloaded to its place.

The pontons will be fixed to each end of the element before a small fleet of tugs pulling them to their position over a 12 meter deep and 100 meter wide ditch, covered in the sludge last year.

The immersion will be supervised from a control room aboard the pontoon. Wire cable winches will be used, a total of more than 200 kilometers to lower the element, while the ballast tanks will be filled with water, helping a safe and stable descent to the bottom of the sea.

Underwater cameras and custom positioning equipment will guide the element to your place with an accuracy of up to 12 millimeters. Giant rubber joints and secondary seals conceived to last 120 years guarantee the tunnel stun.

When the first immersion is done later this year, Juchem estimates that it will take about 40 hours to be completed, including transportation from the work port. Pontão’s crew, consisting of 22 people, is receiving intensive training.

“There will be no test for effective immersion,” says Juchem. “It has to work at first. We will not compromise quality and safety. That’s why we are devoting the time necessary to make sure we are perfectly prepared.”

Vision

The construction of the two portals of the tunnel in Rødbyhavn and Puttgarden is advancing. Both places are two steps from the ports they will replace, reducing 45 -minute ferry travel times to 10 minutes by car and seven minutes by train.

A traveler who wants to go from Hamburg’s train to Copenhagen currently has to take a trip of almost five hours, but this time will be half reduced when the tunnel opens.

“The Fehmanbelt tunnel will be a watershed for tourism in Denmark and the Scandinavian region in general,” says CNN Mads Schreiner, director of Visitdenmark’s international market.

“By significantly reducing travel time between Germany and Denmark, our country will become more accessible than ever to Central European visitors. We hope to watch an increase in autonomous tourism, weekend escapes in the city and sustainable travel options such as train and bicycle tourism.”

“This new connection presents incredible opportunities for destinations in East Denmark, as more travelers will explore beyond copenhagen,” he adds.

According to Schreiner, the tunnel also represents a challenge for Denmark regarding the renewal and expansion of facilities for the expected influx of new travelers.

“It is crucial to ensure that visitors choose to stay and know Denmark, instead of just being passed. By investing in infrastructure and creating attractive experiences for visitors, we can maximize the tourist potential of this historical project.”

Sustainable future

Inevitably, with such a large infrastructure project, concerns about its environmental impact on sea habitats and coastal habitats were raised.

In November 2020, a Federal Court in Germany rejected an appeal against project planning approval due to a series of allegations, including environmental concerns. And in 2022, an emergency request was also rejected to suspend dredging near Puttgarden.

FEMERN A/S claims to be committed to protecting the environment and, in cases where the impacts of construction are inevitable, is creating new natural areas in other locations.

For example, the 15 million cubic meters of seabed materials excavated in dredging were deposited in new land areas recovered in Lolland and Fehmarn.

“These places are part of the natural environment that FEMERN A/S is creating to replace the areas affected by the project and will eventually become wide humid areas with beach meadows, swamps and dry pastures,” wrote Femern CEO Henrik Vincentsen in the company’s 2023 sustainability report.

“FEMERN A/S intends to leave not only more, but also better nature than before the start of the project.”