(CNN) — After more than a decade of planning, work has begun on the world’s longest immersed tunnel. Descending up to 40 meters beneath the Baltic Sea, Fehmarnbelt Tunnel will link Denmark and Germany, slashing journey times when it opens in 2029.
The tunnel, which will be 18 kilometers (11.1 miles) long, is one of Europe’s largest infrastructure projects, with a construction budget of over €7 billion ($8.2 billion).
By way of comparison, the 50-kilometer (31-mile) Channel Tunnel linking England and France, completed in 1993, cost the equivalent of £12 billion ($15.5 billion) in today’s money. Although longer than the Fehmarnbelt Tunnel, the Channel Tunnel, was made using a boring machine, rather than by immersing pre-built tunnel sections.
It will be built across the Fehmarn Belt, a strait between the German island of Fehmarn and the Danish island of Lolland, and is designed as an alternative to the current ferry service from Rødby and Puttgarden, which carries millions of passengers every year. Where the crossing now takes 45 minutes by ferry, it will take just seven minutes by train and 10 minutes by car.