The story of Tokyo’s floating car park, a gigantic structure nestled in the middle of the bay

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When it comes to joining the two shores of a bay, there are those who opt for bridges, those who prefer tunnels and those who, as occurs with the promoters of Aqua Linein Tokyo, come to the simple conclusion that there is no need to deprive yourself of anything and the best thing is to mix.

Faced with the challenge of linking the cities of Kawasaki and Kisarazu, two urban centers located on both sides of Tokyo Bay, the Japanese authorities decided to resort to a viaduct, an underground canal… And, as a bonus, build two artificial islands on the waters of the Pacific, one of them 650 meters and provided with a huge parking and commercial area.

There is nothing.

The project was named Tokyo Bay Aqua-Line and although it was inaugurated a quarter of a century ago, it continues to amaze due to its dimensions, design and the technical solution with which it saves a bay over 14 kilometers wide in which the waters reach 70 meters deep.

An artificial oasis in the Pacific

The challenge that the technicians posed towards the middle of the 20th century was to connect the prefectures of Kanagawa Y chiba, on the Boso Peninsula. In a straight line, crossing the bay, both territories are not even 15 kilometers apart; but by land, moving from one point to another requires driving for 90 minutes through densely populated areas or perform a ferry ride of about an hour.

To make things easier for the residents of the region, the Japanese authorities got down to business at the time and during two long decades They dedicated themselves to studying the best way to build a direct connection between Kawasaki and Kisarazu through the bay that would extend National Route 409.

Sky Bridge 721, this is the new and spectacular longest suspension bridge in the world

The challenge was not easy. First because of the extension of the link, which should have been around 14 kilometers in the middle of the Pacific, and second because of the intense flow of boats that the bay registers.

After many years of analysis and sounding out the ground, it was concluded that it was best split link15.1 km, in four parts: a 4.4 km viaduct (Aqua Line Bridge), a 650 m artificial island (Umihotaru), a 9.5 km tunnel (Tokyo Wan Aqualine Tunnel) and a second, much smaller artificial island known as Torre of wind.


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Construction work lasted about nine years. In 1989 the works to raise the bridge began and on December 18, 1997, after many headaches and an investment of billions of dollarsthe infrastructure was finally opened to the passage of vehicles.

Despite the time that has passed since the inauguration the result continues to surprise. The viaduct, 4.38 km long, is 22.9 m wide. stands on 42 pillars sunk in the waters of the bay. The tunnel has two channels with several lanes and at its deepest point it plunges 45 m. Its outer diameter is 14.1 m and the inner diameter is 11.9. To facilitate its ventilation, the artificial island Torre de Viento was built, in which two enormous vents rise.

The most curious piece of the Tokyo Bay Aqua-Line, however, may be the artificial island Umihotaru, baptized like this in a nod to a kind of crustacean of only 3 mm that lives in the waters on which the mega infrastructure stands. In Tokyo it is also known as Kisarazu and it is probably one of the few parking areas located on an artificial island: it is located in the middle of the Japanese bay, on the waters of the Pacific Ocean and a stone’s throw from the capital.

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The islet is surrounded by the sea and is five levels high. The first three serve as a car park and the last two house visitor-oriented businesses. “It is the only shopping center in the sea where you can enjoy 360 degree panoramic views of Tokyo Bay, as well as many shops, restaurants and services”, highlights Umihotaru’s website.

In addition to restaurants, shops and even the viewpoint with views of Fuji, the islet has a museum that tells the story and the technical challenges that were faced in shaping Aqua-Line.

The panorama that can be enjoyed on the island, its services and the experience of being in the middle of the bay, on an artificial island splashed by the waves of the Pacific and the icy winds of the Japanese winter make it more than just a point of passage. between the cities of Kawasaki and Kisarazu; they elevate it, and in its own right, to the category of tourist attraction. Of course, to get there you will have to scratch your pocket. Crossing the Aqua-Line requires paying a toll that, at least in 2005, it was around 14 euros.

Pictures | Chihaya Sta (Wikipedia), Umihotaru, Park (Flickr), Ume-y (Flickr), Manish Prabhune (Flickr) Y Hideyuki KAMON (Flickr)

When it comes to joining the two shores of a bay, there are those who opt for bridges, those who…

When it comes to joining the two shores of a bay, there are those who opt for bridges, those who…

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