The Fehmarnbelt Tunnel

Lolland Island and Puttgarden, Denmark and Germany

Year

2020 - 2029

Duration

Estimated 9 years

Cost

Estimated €7.4 billion

Location

Denmark and Germany

Project achievements

Connected communities

It will cut travel time between Denmark and Germany

Used engineering skill

Uses prefabricated elements that will be placed on top of the seafloor and joined together

Environment benefitted

The project is powered by renewables and designed for greener transport

Link Denmark and Germany with a Lego-like tunnel

A groundbreaking infrastructure project is underway beneath the Baltic Sea, connecting Denmark and Germany via the Fehmarnbelt Tunnel.

Designed to dramatically cut travel times and enhance connectivity between Scandinavia and mainland Europe, the tunnel is poised to become the world’s longest immersed road and rail link.

An immersed tunnel is a type of underwater passage constructed by sinking prefabricated tunnel sections into a trench beneath the water and covering it up to keep it in place.

Stretching 18 kilometers (11 miles), it will also be Denmark’s largest infrastructure project to date.

The tunnel is a key component of the European Union’s broader strategy to improve cross-border transport while encouraging more sustainable alternatives to air travel.

The total cost of the project is estimated at €7.4 billion, with the majority funded by Denmark and a significant €1.3 billion contribution from the European Commission.

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Immersed tunnelling

Explore how this record-breaking tunnel is being built under the Baltic Sea.

Did you know …

It will shorten travel time between Lolland and Fehmarn from 45 minutes by ferry to 10 minutes by car or seven minutes by train.
The electrified high-speed rail line will be capable of reaching 200 km/h (125 mph).
89 ‘elements’ weighing in at 73,500 tonnes apiece, will be linked together on the seafloor to create the tunnel.

How the immersed tunnel is being built

Unlike most underwater tunnels that cut through bedrock, the Fehmarnbelt Tunnel will sit on top of the seafloor – a remarkable engineering feat.

Its main construction site is located at Denmark’s Lolland Island and features a purpose-built harbour and factory dedicated to producing the tunnel segments, known as ‘elements’.

In total, 79 standard elements and 10 special elements will be manufactured.

The special elements are designed to also house technical systems, like utilities, simplifying the construction and future maintenance of the tunnel.

Each tunnel element measures 217 meters (712 feet) in length and 42 meters (138 feet) in width, constructed from reinforced steel and concrete.

Weighing in at 73,500 tonnes apiece, these colossal structures are a testament to modern engineering.

An illustration of a tunnel segment being lowered onto the seabed. Image credit: Sund & Bælt Holding A/S

Once a tunnel element is ready to be shipped, waterproof bulkheads (barriers) are installed at both ends, and the segment is carefully towed into position by tugboats.

In total, 89 elements will be connected sequentially – much like assembling giant Lego pieces – to form the complete tunnel.

Water is pumped out between the segments to create watertight seals.

Once assembled, crews install the tunnel’s vital systems: railway tracks, ventilation, cameras, comms, signage, and finishes.

Each system will undergo rigorous testing during the final phase of construction, ensuring everything is fully operational ahead of the tunnel’s anticipated opening in mid-2029.

The portal

A portal, or entrance, is built on either side of the tunnel – one in Rødbyhavn, Denmark, and the other in Puttgarden, Germany.

These portals serve as the critical transition points where road and rail traffic enter and exit the immersed tunnel.

Designed to integrate seamlessly with upgraded transport networks on both sides, the portals connect the tunnel to newly built roads and electrified railways.

Beyond their structural role, the portals also house key safety and operational systems, making them essential to the tunnel’s long-term functionality and resilience.

Advantages of an immersed tunnel

Unlike bored tunnels, immersed tunnels are built in sections and placed directly into a trench on the seabed.

This makes them ideal for the shallow waters and soft ground conditions the Fehmarnbelt Tunnel will be placed in.

This method allows for faster construction with less disruption to surrounding areas.

It also provides greater control over alignment and safety features, making it well-suited for mixed traffic like rail and road.

Additionally, immersed tunnels often have a lower carbon footprint compared to long-span bridges or deep-bored tunnels, aligning well with sustainability goals.

Sustainability

The Fehmarnbelt Tunnel is not only a major infrastructure project but also a showcase for sustainable construction.

From the outset, the project has focused on reducing its environmental impact – using lower-carbon concrete, minimising construction emissions, and committing to carbon-neutral operations powered by renewable energy.

Once complete, the tunnel will support greener transport by enabling faster, electrified rail travel, helping shift freight from road to rail.

With circular construction practices, energy-efficient systems, and reforestation efforts to offset the left-over emissions, the Fehmarnbelt Tunnel is setting a new benchmark for climate-conscious infrastructure in Europe.