The project would be the first of its kind in the world.

A cutaway view of an SMT. (Norwegian Public Roads Administration)

The fjords that make Norway’s coast so breathtaking also make the landscape exceedingly time-consuming to navigate. A drive on the main coastal artery, E39, from Stavanger to Sogneford is less than 250 miles, but takes more than seven hours, traversing as it does countless high-cliffed glacial inlets carved miles into the coasts. These are stunning-but-arduous treks for tourists, and time and productivity lost for locals.

Conventional bridges and tunnels sound like obvious solutions, and Norway has its fair share of those. But those come with their own problems: the floor of every fjord has its own delicate geology, bridges can disrupt maritime activities, and steel trusses risk sullying the pristine natural beauty.

A hybrid approach to the coast’s impassability might be the ticket, and it looks as if one could actually get built. Norway’s public roads administration has proposed building the world’s first “submerged floating tunnels” along E39. These would be, essentially, tubes sitting up to 100 feet beneath the water’s surface, tethered to floating pontoons and seabed anchors. Officials estimate that a permanent system of these crossings could cut trip times along the coast in half, at a cost of $25 billion, according to WIRED’s Aarian Marshall. Sognefjord may be the ideal test-site for the first one, reports Marshall: “The structure would be made up of two curved, 4,000-foot long concrete tubes—one for each direction—hanging 65 to 100 feet below the surface.”

One challenging section of E39. (Google Maps)

Though these would be the world’s first SFTs, building them wouldn’t be as crazy as it sounds. The engineering principles and technologies would apparently draw on those found in floating bridges, offshore drilling platforms, and tunnel blasting. Plenty of important unknowns have yet to be worked out—the particulars of the sea floor, the effects of wind and waves, and the possibility of boat and submarine crashes, for instance. But officials and researchers seem to think these can be hurdled. “To a submarine an SFT is one of very many under water obstacles,” one Norwegian engineer stated pragmatically in a 2010 research paper.

The floating tunnels aren’t a done deal yet, and other bridge and tunnel alternatives are on the table (this video offers a sense of other options). But if Norway chooses the submerged route, it could be a step forward for even longer-distance, undersea tunnels—think transatlantic tubes—as CityMetric points out. Sounds like an idea worth floating.

Another view of an SMT. (Norwegian Public Roads Administration)

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