Immersed tunnels


Stephen Whitham

Stephen Whitham

Global Division Unit Manager, Tunnels
T: +45 51615202

Immersed tunnels (also called immersed tubes) are most often used to cross a river or sea. The process of immersed tunnel engineering begins with the construction of concrete segments, which are then floated to the tunnel site. At the site, they are sunk into place in a narrow trench below the sea- or riverbed, and linked together. 

The 4,050 m immersed tunnel, carrying a dual-track railway and four-lane motorway from Copenhagen to an artificial island – a part of The Øresund Link between Denmark and Sweden – was the longest immersed tunnel in the world, when inaugurated in 2000.

The world's longest immersed tunnel

In 2009 a Joint Venture with Ramboll as lead partner won the design competition for a 18 km long immersed tunnel across the Fehmarn Belt between Germany and Denmark. This will be a new record-breaking tunnel, more than three times as long as any existing immersed tunnel. It will also be the longest tunnel yet to be designed in accordance with EU Directive 2004/54/EC on road tunnel safety, and will set new standards for modern tunnel design. The immersed tunnel solution under Fehmarnbelt is a study in innovative thinking, as it challenges existing tunnel building standards. It improves functionality through its pioneering longitudinal ventilation system and state-of-the-art safety and security features.

The total length of the Fehmarnbelt tunnel will be approx. 18 km from tunnel mouth to tunnel mouth. At a speed of 110 km per hour, this will offer motorists a journey time of approximately 10 minutes through the tunnel. For train passengers, the journey will take seven minutes from coast to coast.


External information about immersed tunnels

Femern Belt

Visit Femern Sund Bælt's website to read more background about the project and see their many videos and visualisations.


Øresundsbron AS is the company for the combined immersed tunnel and bridge crossing between Denmark and Sweden.

Tunnel Engineering brochure

Tunnel Engineering brochure (PDF, 1 MB)


Engineers discussing the Fehmarnbelt tunnel

Fehmarn: The world's longest road/rail tunnel

In the future Scandinavia and the rest of Europe will be connected by the world's longest road and rail tunnel.

Øresund bridge

The Øresund Link

The Øresund Link connects the Danish capital Copenhagen with the city of Malmö in southern Sweden by a four lane motorway and a two track electrified railway for high speed (200 km/h) passenger services as well as freight trains.


The population in Western part of Sweden is growing and capacity problems on the railways in and around Gothenburg are increasing.

Maintenance of the Limfjord Immersed Road Tunnel

Ramboll was chosen to undertake overall repairs on the Limfjorden immersed highway tunnel, which has a total length of 550 meters.

Vlatava River Crossing

The tunnel consists of two tubes app. 6.5m x 6.5m each with a total length of app. 170m. A new technology for immersion, sliding and pulling under water has been invented for this project.

Päijänne Water Tunnel

Refurbishment of Päijänne Water Tunnel

Supervision of the refurbishment of the worlds’ longest rock tunnel that carries water to the capital of Finland. Finland’s Päijänne Water Tunnel (constructed in 1972) is the world’s longest continuous rock tunnel and provides Helsinki and surrounding cities with pure water from Lake Päijänne in central Finland.

Show more projects for this service


First Floor, Emerald Building
Oud Metha Road
PO Box 116921, Dubai, UAE
Tel: +971 4 334 3616
Fax +971 4 334 3617


Other sites

Other sites