Underwater Tunnel: Which is the world’s longest?

England and France behind Japan

In 1888, Michel Verne, the son of the more famous writer, Jules Verne, published a story called “Un Express de l'avenir” - “A Future Express” - where he told of an imaginary transatlantic tunnel. Since then, the idea of building an underwater tunnel capable of connecting London to New York, quickly, kept on finding its way back someway. Despite the latter project still being just a fantasy, many of the existing underwater tunnels, once also just a mere fantasy, are today a reality, being used by cars and trains every day. And if today's longest underwater tunnel brings such amazement with it, in a few years' time the amazement will be even greater. In fact, underwater sea tunnels are being conceived, today, which will be even longer than today's longest. A particular project will actually be more than twice longer the current record breaking one.

The world's longest underwater tunnel

Which is the longest underwater tunnel? The answer to this question is not an easy one, as it depends on different points of view.The candidates, in any case, are two: the Seikan tunnel, in Japan, and the Channel Tunnel, the ultra-famous underwater tunnel connecting France to England. The Japanese measures 53.85 km in length, while the Channel one measures 50.45 km. so, first beats the English one with its three additional kilometres. Despite this, it's not as easy as this. The Channel Tunnel, in fact, has the longest underwater section, with 39 km against the 23 km of its Japanese rival.

Nevertheless, the title of the world's longest still goes to the Seikan tunnel. The Japanese tunnel was built in 1971, and works concluded in 1988. It was built to connect Honshū Island (Japan's largest with Tokyo, Hiroshima, Kawasaki, Kobe, Kyoto…) to Hokkaidō Island. The idea of this very long underwater tunnel was being thought about already since the first years of the '900s. It was made into reality only after the end of the Second World War, especialy after 4 ferries sank after being hit by a typhoon, with 1,430 people dead. Building the tunnel was not an easy task at all due to the complex geological context. The final costs amounted to $3.6 billion, also due to the floodings that occured during construction, a much greater amount, compared to the expected one. During works 34 workers lost their lives.

The Channel Tunnel (which in any case is the third longest tunnel in the world, after the St Gotthard one - and, obviously, the Seikan one) was built between 1987 and 1994. In this caso too costs grew bigger than expected reaching over £10 billion 8compared to the initially estimated amount of £3) The tunnel was concieved through intertwining ideas that grew over a long period of time. In fact, in 1802, just by way of example, an undewater tunnel for horse-drawn carriages was already thought of.
The Channel Tunnel is made of 3 parallel tunnels. The two external ones are reserved for trains, while the internal one, a service one, is dedicated to road transport. It is used to allow vehicles, used for maintenance purposes on the tunnel, to move freely along it, while also acting as an exit, in case of an emergency.

The world's longest underwater tunnel that you can drive through by car

If the Seikan and the Channel tunnels are the two world's longest, there still is another competitor, which instead has a record for the number of wheeled vehicles driving along it. The underwater tunnel connecting Denmark to Sweden is in fact the world's longest one used for rail and road transport, extending for over 8 km. Even more astonishing than the length is its cleverness. This underground tunnel is in fact part of the large Øresund bridge that connects Copenhagen to Malmö. This structure that was inaugurated in 2000 crosses the sea for 16 km. The actual bridge stays above sea level for 8 km to then leap under the waters - where there's an artificial island.

Underwater tunnels being built

Many other underwater tunnels are being built during these years. Some, just lile the Øresund one, stand out for the genius behind the project. This is exactly the case, to remain in Scandinavia, of the underwater tunnel being studied in Norway to ease traffic from the northern part of the country to the south, while crossing, one by one, the many fjords that cut into the coast. It is an ambitious and very costly project requiring a €25 billion investment. It foresees the construction of many sequential underwater tunnels built at an average depth of 30 metres under sea level. Among the people responsible for the project there’s the Chief Engineer of the Norwegian Public Road Administration, the Italian Arianna Minoretti.

Still, in Northern Europe, an underwater tunnel that will connect Helsinki to Tallin stands out due its great extension. This enormous tunnel should be built mainly through Chinese fundings, to be collected among the funds established to build the New Silk Road. It will, as it passes from Finland to Estonia, reach 100 km in length, therefore becoming the world's longest.

Or maybe not. The same Chinese people funding this tunnel in the Baltic Sea are also preparing to build a tunnel under the Bohai Sea, between Dalian, in the northern province of Liaoning, and Yantai, in the western province of Shandong. These two cities are currently connected through a 1,400 km-long road, taking 8 hours to go from one to the other. The underwater tunnel, once built, will allow people to travel between the two cities in just 40 minutes. When built - probably by the end of 2026 - it will measure 123 km in length, therefore it will be even longer than the sum of the lengths of the Seikan and Channel tunnels together.