TECH
Floating tunnels could carry cars beneath deep fjords and lakes
Submerged pontoons promise a new way to cross waters too wide or deep for bridges
In fjords that are too deep for traditional bridges and too wide for regular tunnels, engineers are exploring submerged floating tunnels, or SFTs. These would hang beneath the surface, held up by pontoons or cables. Cars would drive through watertight tubes—a novel solution to Norway’s geographic challenges.
Technical advances in this concept include:
Suspended structure: SFTs would sit 20–30 meters below, avoiding waves while remaining accessible for anchoring or floating pontoons. Feasibility was studied by Norway’s Public Roads Administration under its E39 corridor upgrades.
Engineering feasibility: Earlier feasibility studies, including the Høgsfjord case, proved SFT concepts for spans of ~1,400 meters are structurally viable.
Cost and environmental benefits: Analysis shows SFTs could cost just a third of a suspension bridge and leave a lighter environmental footprint—if environmental and lifecycle risks are carefully assessed.
In 2013, a $24.5 billion plan for SFT segments and floating bridge sections along E39 was officially floated. That proposal included a 4 km-long SFT crossing fjords otherwise impossible to bridge conventionally.
Subsequent reports confirm that SFTs remain part of Norway’s long-term vision for a ferry-free E39, helping slash travel time between Kristiansand and Trondheim.
That’s not all: Parallel to Norway’s work, research teams in Italy and China are modeling SFTs to connect deep lakes and coastal spans, using advanced numerical modeling and structural simulation.
Floating tunnels are not yet a reality—but analysts say they could be achievable by 2050 as materials, marine engineering, and modeling capabilities advance. If successful, SFTs could reshape how we connect regions across deep-water gaps.