The longest underwater tunnel in the world is under construction and will connect Danmark and Germany

The project costs about eight billion dollars, and in addition to the railway connection, the tunnel will also have a four-lane highway. It will be the longest underwater tunnel, and also the longest rail-car tunnel in the world.

The construction site was visited by King Frederik the Tenth for the laying of the first 217-meter-long concrete segment, and there will be a total of 79 of them by the end of the project, reports RTS.

The total length of the “Immersed” tunnel will be 18 kilometers. It will be placed on the bottom of the Baltic Sea in a trench 40 to 50 meters wide and 12 to 15 meters deep.

The tunnel is a key component of the Scandinavian-Mediterranean Corridor, a transport network that stretches almost 5,000 kilometers from the Mediterranean Sea to Finland. The corridor crosses the ocean and passes through the Alps, but when it reaches Scandinavia, the Fehmarn Strait forces travelers to detour 450 kilometers.

The planned rail-car connection will shorten the journey from Hamburg to Copenhagen from five to less than three hours, and what takes 45 minutes by ferry will be completed in ten by car and seven by train.

Traffic in the underwater tunnel will run through separate tunnel tubes, one for each direction. The tunnel will include an emergency lane and will be constantly monitored by cameras from a control center in Copenhagen.