Experts say it is an engineering marvel unlike anything seen before.
On the shores of the Baltic Sea, in southern Denmark, work is in full swing on one of the most ambitious infrastructure projects in Europe. The Fehmarnbelt submarine megatunnel will reshape the continent’s road and rail network, connecting Denmark and Germany beneath the sea.
The Fehmarnbelt tunnel is a technical marvel that will link Central Europe with Scandinavia, and once completed in 2029, it will be one of the most important transport corridors in Europe.
It is one of the largest infrastructure projects in Europe, with construction costs exceeding seven billion euros. For comparison, the construction of the 50-kilometer-long Channel Tunnel under the English Channel cost 13.7 billion euros. The Channel Tunnel was built using a tunnel boring machine rather than by submerging pre-built segments into the sea.
Fehmarnbelt will thus be the longest road-rail tunnel and the longest ‘immersed’ tunnel in the world. Unlike conventional construction methods, it is assembled from pre-built concrete segments, which are placed into trenches dug on the seabed, connected, and then covered with sediment.
The project consists of 79 colossal concrete segments, each 217 meters long, 42 meters wide, and weighing a massive 73.000 tons – equal to the weight of ten Eiffel Towers.
The 7.4-billion-euro project includes the construction of an 18-kilometer-long tunnel with two traffic lanes in each direction and two railway tracks. It will be positioned up to 40 meters below the surface of the Baltic Sea, connecting the Danish town of Rodby with the German town of Puttgarden, and creating additional road and rail links between Central Europe and the Scandinavian countries.
Last month, in February 2025, the first prefabricated concrete segments left the factory in Rodbyhavn, Denmark, marking the beginning of a crucial phase of the project.
Alongside the large concrete segments, ten shorter segments, each 39 meters long, will be installed to house technical installations.
The placement process is extremely precise and complex – the segments will be lowered using special ships and pontoons, named Ivy 1 and Ivy 2, which will ensure their safe positioning in a trench 100 meters wide and 12 meters deep. This will also be done using steel cables over 200 kilometers long, while underwater cameras and sophisticated positioning systems will ensure precision.
The tunnel will feature special rubber seals and secondary protective layers designed to ensure watertightness and durability for 120 years.
Travel time will be drastically reduced
The construction of Fehmarnbelt will significantly shorten travel times between Denmark and Germany. Currently, the ferry crossing between Rodbyhavn and Puttgarden takes 45 minutes, whereas through the tunnel, cars will pass in just ten minutes, and trains in seven minutes. Train travel between Hamburg and Copenhagen, which now takes nearly five hours, will be cut in half.
The tunnel will also benefit freight trucks and trains, reducing the land route between Sweden and Central Europe by 160 kilometers. In Denmark, it is referred to as the “strategic corridor between Scandinavia and Central Europe.”
According to Mads Schreiner from the tourism organization VisitDenmark, the tunnel will be a key factor in the development of tourism in Denmark and across Scandinavia.
“The new tunnel will significantly increase Denmark’s accessibility for visitors from Central Europe, encourage weekend travel, and promote sustainable forms of tourism, such as train travel and cycling,” he stated, Biznis Info writes.
