Engineers have lowered the first of 89 giant concrete sections onto the seabed of the Fehmarn Belt, marking a major milestone in the construction of the undersea tunnel that will link Denmark and Germany.
The 217 metre element, which weighs about 73,500 tonnes, left the work harbour at the tunnel factory near Rødbyhavn on the Danish island of Lolland on 4 May 2026. It was guided into position in front of the Danish tunnel portal and immersed three days later, after an operation that took around 14 hours.
Femern A/S, the state owned Danish company managing the project, said the remaining 88 elements will be immersed one by one over the coming years and joined to form a continuous structure 18km long beneath the Baltic Sea.
When finished, the tunnel will carry both road and rail traffic between Rødbyhavn and Puttgarden on the German island of Fehmarn, replacing the existing ferry service and sharply cutting travel times across northern Europe.
How the tunnel is being built
The project uses an immersed tube method rather than traditional boring. Each section is cast on land at the factory near Rødbyhavn, sealed at both ends and filled with air, then floated to the site and lowered into a trench dredged into the seabed up to 40 metres below the surface.
For the first immersion, contractors added 4,500 tonnes of ballast concrete to make the element heavy enough to sink. Five tugboats and the purpose built immersion vessel IVY towed the section to its position, where a high precision alignment system lowered it onto a prepared gravel foundation. The element was then connected to the portal using hydraulic arms, with laser measurements confirming the final position to millimetre level accuracy.
Each unit contains five tubes: two for the motorway, two for the railway and one service tube for technical installations. Because the road tubes are heavier than the rail tubes, temporary water chambers in the outer railway tube keep the element horizontal during immersion.
Cost, timeline and delays
The tunnel is being delivered by Femern Link Contractors, a consortium working with companies including the DEME Group, under the management of Femern A/S, a subsidiary of Sund & Bælt. The construction budget is more than 7 billion euros.
The European Commission has designated the scheme a priority project and awarded it roughly 1.3 billion euros in construction funding. The link will be paid for by user charges once it opens.
Construction began in 2020 after more than a decade of planning. The tunnel was originally due to open in 2029, but Danish officials have indicated it is unlikely to enter service before 2031.
What it means for travel and trade
The tunnel will cut the crossing between the two coasts to about seven minutes by train and ten minutes by car, compared with the 45 minute ferry. It is also expected to reduce the train journey between Copenhagen and Hamburg to around two and a half hours.
Planners say the link will strengthen the high speed rail corridor between Stockholm and Hamburg, shift freight from road to rail and support economic activity by making cross border travel and logistics faster.
At 18km, the structure will be the longest immersed tunnel in the world once complete, more than three times the length of the current record holder, the 5.8km Transbay Tube in San Francisco. The placement of the first of its 89 sections marks the start of a long sequence of immersion operations that will continue in parallel with work on the portals, ramps and land side infrastructure.
