The Fehmarnbelt Tunnel is one of those infrastructure projects that sounds almost futuristic when you first hear about it. When it opens later this decade, drivers and train passengers will be able to travel directly under the Baltic Sea between Denmark and Germany through one of the longest immersed tube tunnels ever constructed.
To Americans accustomed to major projects like the Chesapeake Bay Bridge-Tunnel or the Boston Excavation, the scale of this European megaproject puts it in a similar category: expensive, complex and potentially transformative for regional travel.
The fixed line across the Fehmarn belt will be an immersed tunnel connecting the Danish island of Lolland to the German island of Fehmarn. When completed, the line will replace the current 45-minute ferry and become a direct motorway and rail link to the undersea Baltic Sea.
The tunnel is expected to open to traffic in 2029 and will become one of the longest immersed tube tunnels in the world.
Project scope, length and financing
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The Fehmarnbelt tunnel project will span approximately 18 kilometers (approximately 11 miles) across the Baltic Sea between Denmark and Germany. When completed, it will have a four-lane motorway and a double-track electrified railway, allowing cars and trains to travel between the two countries without relying on ferries.
According to project developer Femern A/S, the tunnel will be the longest immersed road and rail tunnel ever constructed. Rather than being drilled deep into the rock, the tunnel will be assembled from a large number of precast concrete sections that are placed in trenches on the ocean floor and connected underwater.
The total cost of the project is estimated to be approximately €7.4 billion (approximately US$8 billion). Most of the funding is provided by Denmark, which will recoup its investment through tolls once the tunnel opens. The EU’s European Connectivity Fund has also contributed more than €1 billion, as the route is considered an important part of the European transport network linking Scandinavia to Central Europe.
Once the tunnel opens, travel time is expected to be significantly reduced. Currently, the ferry trip between Rødbyhavn, Denmark, and Puttgarden, Germany, takes approximately 45 minutes. Project planners say the tunnel will reduce journey times to about 10 minutes, while train journeys between Copenhagen and Hamburg could be reduced by about two hours.
Maritime safety and operational security
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As the Fehmarn Belt is a busy shipping corridor in the Baltic Sea, one of the main engineering priorities is to ensure that the tunnel does not interfere with maritime traffic.
The tunnel will sit in a trench on the ocean floor and then be covered with a layer of sand, gravel and rock. This means ships passing overhead won’t encounter any structural obstacles, unlike bridges which require large support towers in the water.
Safety systems within the tunnel are designed to meet or exceed modern road tunnel standards. According to Femern’s project documents, the road tunnel will include continuous emergency lanes, surveillance systems, ventilation controls and emergency exits connecting the road tunnel to separate service corridors.
The safety features are similar to those used in other large Eurotunnels, such as the Oresund Tunnel, which is part of the famous Oresund Bridge-Tunnel connection between Denmark and Sweden.
Landmark engineering achievement
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The scale of the project is extraordinary from an engineering perspective. According to analysis by the Institution of Civil Engineers, the Fehmarn Belt Tunnel will be constructed using 89 large prefabricated tunnel elements.
Each component is approximately 217 meters (712 feet) long and weighs 73,500 tons. Once construction was complete, watertight bulkheads sealed the ends of the segments, allowing them to float. Tugboats then pull the element into place, carefully lowering it into prepared trenches on the seafloor.
Once aligned, this section will be connected to the previous section, sealed and buried under a protective layer of seafloor material. Engineers often describe the process as assembling giant Lego bricks underwater, even though each Lego brick weighs more than many Navy ships.
Once completed, the Fehmarn Belt Tunnel will become a key link in the Scandinavian-Mediterranean transport corridor, connecting Northern Europe with major cities and freight routes across the continent. Supporters say it will improve trade, shorten travel times and reduce congestion on ferry routes.
For drivers and train passengers traveling across Northern Europe, it will also offer something that still feels a bit surreal: the chance to cross an international border while traveling through the Baltic Sea Tunnel.
This article was originally published on Autorepublika.com and is republished with permission from Guessing Headlights. Use AI-assisted translation, followed by human editing and review.
This article originally appeared on Speculation Headlights: Engineers are using giant 73,000 tons of LEGO bricks to build an 11-mile undersea tunnel
