Inside the world’s largest immersed tunnel built without a single boring machine

An undersea shortcut is about to redraw northern Europe’s travel map. Built with immersed-tube engineering rather than a TBM, the Fehmarnbelt link will compress journeys and streamline freight across the Baltic.

A shortcut under the sea

I can still remember shivering on the deck of a ferry making the crossing between Germany and Denmark, rain lashing sideways and a mug of lukewarm tea doing very little to help. The 45-minute journey felt twice as long in that weather.¹ Soon, though, travellers won’t need to endure the Baltic breeze at all — a trip that once demanded patience and a good coat will take just minutes, thanks to an engineering feat put together not with a tunnel boring machine, but with sheer precision and planning.

A new link in Europe’s transport puzzle

The Fehmarnbelt Tunnel will stretch 18 kilometres beneath the strait, joining Puttgarden on Germany’s Fehmarn Island to Rødby on Denmark’s Lolland Island. Trains will race through in about seven minutes, cars in roughly ten.² The link is designed to ease cross-border travel and support greener, more direct routes across the region.

Did you know?
A single fixed link removes vehicle queuing and weather-related boarding delays that can extend nominal ferry times during rough conditions.

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Building giants beneath the waves

This is no ordinary tunnel. Instead of drilling, engineers are casting massive concrete segments onshore — each standard element is 217 metres long and weighs around 73,500 tonnes. They’re sealed with watertight bulkheads, floated into position and lowered about 40 metres under the sea. In total, 79 standard and 10 special elements will form the link, aligned under water with tolerances of mere centimetres.³

Did you know?
At full pace, the factory turns out roughly one standard element every two weeks in climate-controlled halls — industrialised tunnel-making.

More than just a time-saver

Once open, the tunnel is projected to cut the Copenhagen–Hamburg rail trip to about 2½ hours as associated upgrades are completed — a step change for travellers and logistics alike. That’s not just good news for holidaymakers: freight operators stand to benefit as shorter, more direct rail routes can reduce journey times and overall CO₂ compared with today’s ferry-plus-detour options.⁴

A case study in cooperation

Beyond the steel and stone, the Fehmarnbelt Tunnel is a symbol of what can happen when neighbours plan together. The project is developed by Femern A/S, a Danish state-owned company, using a user-financed model backed by state-guaranteed loans to be repaid from tolls, alongside EU support; Germany is responsible for its hinterland rail upgrades. The overall budget framework is set in Danish law at DKK 55.1 billion (2015 prices), with opening aimed for 2029.⁵ For anyone who’s ever stood on that windy ferry deck watching the horizon creep closer, the thought of swapping the chill for a swift, warm train ride will be very welcome indeed.

Footnotes

1. Scandlines — Crossing time for Puttgarden–Rødby: https://www.scandlines.com/practical/crossing-times/

2. Femern A/S — Information to Mariners (facts, length, travel times): https://femern.com/media/nkmgrizt/8900-fem-info-til-det-marine-folk-mobilversion_3_uk_web.pdf

3. Femern A/S — Building the tunnel (element size/weight; production; method): https://femern.com/the-construction/building-the-tunnel/

4. German Federal Ministry for Digital and Transport — Fehmarnbelt Fixed Link (TEN-T; ~2½h rail time): https://www.bmv.de/EN/Topics/EU-Policy/EU-Transport-Policy/Fehmarnbelt/fehmarnbelt-fixed-link.html

5. Sund & Bælt — Finance of the Fehmarnbelt link (budget framework; user-financed model): https://sundogbaelt.dk/en/about-us/finance-economics/construction-costs/finance-of-the-fehmarnbelt-link/