Fehmarnbelt - The world's longest undersea tunnel

Denmark and Germany will soon be connected by an 18km underwater tunnel. The project is expected to be completed in 2029.

After more than a decade of planning, construction on the Fehmarnbelt tunnel began in 2020, months after the completion of a temporary port on the Danish side that will house the factory that will build the 89 massive concrete sections that will make up the tunnel, CNN reported on September 20.

The Danish factory will assemble 89 tunnel sections. (Photo: Femern A/S)

'The first production line is expected to be ready by the end of this year or early next year,' said Henrik Vincentsen, CEO of Femern A/S, the Danish company in charge of the project. 'We will be ready to sink the first tunnel section by early 2024.'

The 18km tunnel is one of Europe's largest infrastructure projects, costing more than $7 billion. By comparison, the 50km Channel Tunnel between Britain and France, completed in 1993, cost $13.6 billion at today's exchange rates. Although longer than the Fehmarnbelt, the Channel Tunnel was built using tunnel boring machines rather than burying pre-fabricated tunnel sections.

The new tunnel will run through the Fehmarn Belt, a strait between the German island of Fehmarn and the Danish island of Lolland, and is designed to replace the current ferry service from Rødby and Puttgarden, which carries millions of passengers each year. Instead of the 45-minute ferry crossing, the journey will be reduced to seven minutes by train and 10 minutes by car. Officially called the Fehmarnbelt Fixed Link , it will also be the world's longest combined road and rail tunnel. It will consist of two dual-lane motorways, separated by a service corridor and two tram tracks.

'Currently, if you go from Copenhagen to Hamburg by train, it takes about 4.5 hours,' says Jens Ole Kaslund, technical director at Femern A/S. 'When the tunnel is completed, the same journey will only take 2.5 hours. A lot of people fly between the two cities, but in the future the train will be better.'

In addition to the benefits for passenger trains and cars, the tunnel will also have a positive impact on freight trains and trucks by creating a road route between Sweden and Central Europe that is 160km shorter than it is today.

The mega project is worth up to 10 billion euros, of which the European Union contributes 1.1 billion euros.

The tunnel will be built 40 metres below the Baltic Sea using 89 giant concrete sections. They will be pre-built on land and then lowered into the water by crane. Femern A/S, the Danish state-owned company behind the project, hopes to have the first section ready to ship by 2024.

Visualization of how concrete is constructed when transferred to water. (Photo: Femern A/S).

Once in place, the concrete sections will be fitted together and other elements such as rail tracks, ventilation systems and cameras will be installed. Some environmental groups have raised concerns about the impact the tunnel will have on wildlife in the Fehmarn belt – an EU-protected area.

_{However, Fermern A/S says the tunnel will increase capacity and reduce congestion on Denmark's rail and road networks. The company also claims the project will result in significant savings in time, energy, fuel and CO2} emissions .