The world’s longest immersed tunnel, set to slash journey times between Denmark and Germany, is under construction beneath the Baltic Sea. This infrastructure will be the longest combined road and rail tunnel anywhere in the world, with two double-laned motorways and two electrified rail tracks. 

The Fehmarn Belt Fixed Link, also known as the Fehmarn Belt tunnel, is an under-construction immersed tunnel, which will connect the Danish island of Lolland with the German island of Fehmarn, crossing the 11-mile Fehmarn Belt.

It is set to be completed in 2029 after construction began in 2020, following a decade of planning. The first element was inaugurated in June by King Frederik X of Denmark. 

The tunnel is designed as an alternative to the current ferry service that runs from Rodby and Puttgarden and carries millions of passengers a year. Once the link is completed, the journey will last just seven minutes by train and 10 by car, while the ferry trip currently takes 45 minutes.  

“Today, if you were to take a train trip from Copenhagen to Hamburg, it would take you around four and a half hours,” said Jens Ole Kaslund, technical director at Femern A/S in 2022. “When the tunnel [is] completed, the same journey will take two and a half hours.

“Today a lot of people fly between the two cities, but in the future it will be better to just take the train,” he added. 

The tunnel will also benefit freight traffic, creating a land route between Sweden and Central Europe that is over 99 miles shorter than the current journey. 

Michael Svane of the Confederation of Danish Industry, one of Denmark’s largest business organisations, told CNN in 2022: “The Fehmarnbelt tunnel will create a strategic corridor between Scandinavia and Central Europe. The upgraded railway transfer means more freight moving from road to rail, supporting a climate-friendly means of transport.  

“We consider cross-border connections a tool for creating growth and jobs not only locally, but also nationally”. 

The Fehmarn Belt fixed link is one of Europe’s largest infrastructure projects, costing $7.1 billion, or £5.6 billion. On the Danish side, east of Rodbyhavn, the factory that will build 89 huge concrete sections that will make up the tunnel was completed last year. 

The Fehmarn Belt is being built by immersing pre-built tunnel sections, unlike the Channel Tunnel which was made using a boring machine. Each section will be 217 metres long, 42 metres wide and nine metres tall, each weighing 73,000 metric tonnes, according to CNN. 

There have been environmental concerns surrounding the project, but Michael Lovendal Kruse of the Danish Society for Nature Conservation argued that the link will bring benefits. He said: “As part of the Fehmarnbelt Tunnel, new natural areas and stone reefs on the Danish and German sides will be created. Nature needs space and there will be more space for nature as a result.

“But the biggest advantage will be the benefit for the climate. Faster passage of the Belt will make trains a strong challenger for air traffic, and cargo on electric trains is by far the best solution for the environment.”