The Fehmarnbelt Tunnel project, which will link Denmark and Germany, has reached a significant stage with the successful immersion of its first tunnel element.
This event marks the start of underwater construction for what will become the world’s longest immersed tunnel at 18km, surpassing the current record held by San Francisco’s 5.8km Transbay Tube.
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Immersion operations began late on 4 May, when the first concrete segment was transported from Rødbyhavn, Denmark, to its seabed position by five tugboats and the specialist vessel IVY.
By midday of 6 May, crews initiated the delicate immersion process, taking approximately 14 hours to accurately position the tunnel segment within the underwater trench near the Danish portal.
Following placement, hydraulic arms fixed the segment to the tunnel portal, and laser measurements confirmed its precise position.
Subsequent steps included placing gravel along the sides of the segment using a dedicated vessel to secure it. This marks the first use of series-produced tunnel elements of this scale in such a project.
Each standard segment measures 217m in length, comprises five tubes for road and rail traffic, and weighs over 73,500t.
Over the coming years, the project will immerse 89 additional elements, which will ultimately complete the link.
The tunnel is being built through a partnership of consultants, Arup, Rambøll and Tunnel Engineering Consultants (TEC), working for the client, Femern, since 2008.
The project falls under the European Commission’s TEN-T programme and has received €1.3bn ($1.5bn) in funding.
Engineers from several European nations have contributed technical expertise to the tunnel’s design and construction, with a focus on improving regional rail and road connections.
European Commissioner for Sustainable Transport and Tourism Apostolos Tzitzikostas said: “The immersion of the first tunnel element is a historic achievement.
“The tunnel will connect regions more closely and create new momentum between Malmö, Copenhagen, Hamburg and onwards into Europe. The European Commission will continue to support this project all the way.”
Once completed, the Fehmarnbelt Tunnel will offer a two-lane motorway and double-track railway, reducing travel times between Copenhagen and Hamburg from five hours to 2.5 hours by train and enabling a car crossing in ten minutes.
The tunnel will support freight movement by rail, aligning with efforts to create a more sustainable transport network across Europe.
The project also includes three key civil engineering contracts: the TPR contract covering tunnel portals and ramps; the TDR contract responsible for dredging and land reclamation; and the TUX contract, which governs the construction and placement of the tunnel elements.
At full scale, the tunnel’s deepest section sits 45m beneath sea level, with the track situated around 40m below water.
The worksite at Rødbyhavn spans 200ha and includes a large factory for producing tunnel segments, as well as an operational port for transporting them to the seabed.
Scheduled to open in 2029, the Fehmarnbelt Fixed Link is set to become a key part of Europe’s transport infrastructure, boosting trade and improving mobility between Scandinavia and mainland Europe.
