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World's first submerged floating tube bridge lined up for Norway

The Norwegian parliament (Stortinget) has moved forward in its studies whether to build submerged floating tube bridges along the E39 Coastal Highway Route between the cities of Kristiansand and Trondheim in West Norway.

Currently the E39 runs along the rugged west coast of Norway, where harsh weather conditions can make travel unpredictable. Road closures are frequent and ferry services are often cancelld because of snow, heavy winds or high waves. The route runs through six counties, and the cities of Stavanger, Bergen, Ålesund and Molde. Total travel time is around 21 hours, and road users have to use seven different ferry connections.

A spokesperson said: “To replace today’s seven ferries, we are planning to build alternative constructions, either bridges or tunnels. We are considering a new type of structure, a submerged floating tube bridge (SFTB), for some of the deepest and longest fjords exposed to harsh weather conditions, where also suspension bridges or floating bridges will be difficult to build.”

Preliminary estimates show that the required improvements will cost approximately NOK340bn (£30.3bn) and would cut the route by 50km reducing travel time by half.

The SFTB would be considered when a fjord is deeper than several hundred metres deep or wider than 2km to 3km, and where existing engineering solutions cannot be applied.

“The seabed would be too deep for a traditional rock tunnel because it will imply the use of a huge amount of land on the shores,” the spokesperson said.

According to the research, floating bridges and other type of bridges on tension leg platforms (TLP) would be susceptible to harsh weather conditions such as strong waves and currents, even if they are suitable for deep crossings, .

The tube would be placed underwater, below shipping lanes but not so deep that high water pressure needs to be dealt with—usually 20m to 50m. Tethers anchored to the seabed or pontoons floating at the surface would provide the vertical stability.

The Norwegian government is currently performing tests to see what the driver experience will be and factoring fires and explosions into the design, as well as ship collisions or submarine collisions, as the fjords are a training field for the Norwegian navy.

Norwegian Public Roads Administration chief engineer Arianna Minoretti said: “The submerged floating tube bridge is certainly an engineering marvel, but the idea isn’t new. The first known proposal was in 1886 by UK naval architect Sir James Edward Reed.

“In Norway the idea was studied since 1923 and, after the studies performed by the Norwegian Public Road Administration for the E39, we know that several other countries are considering building the same type of structure.

“We are in dialogue with several of them, so it is more of a collaboration than a competition, but I have to admit that it will definitely be exciting to see who will be the first country to build this structure. We are still evaluating some fjords the SFTB might be relevant for, and some of them are among the longest and deepest.”

The Norwegian Public Roads Administration is the contractor for the entire 1,100km scheme. 

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