I recently saw the film Transatlantic Tunnel (from 1935) (apparently also called The Tunnel) on Netflix. It was terrible in the sense that almost every movie from before 1936 was terrible since people didn’t really know how to make decent films (except It Happened One Night), but it is also interesting as a period piece.
All sorts of cool technologies are displayed, including Transatlantic Aviation (in single person aircraft), wireless video communication, as well as various plot devices (Allanite Steel, some new drilling technologies etc.). Apparently, after the war (some more prescience here), there is some alliance of the English Speaking Peoples, and Parliament and Congress are connected via Video technology.
The plot (and I am not giving anything away here) is that an engineer-entrepreneur who recently completed the Channel Tunnel (in the 1950s, only off by 40 years or so, this is science fiction), wants to build a tunnel from England to America. He must obtain financing.
His career takes all his time and destroys his marriage. There is an “unforeseen volcano” in the middle of the Atlantic Ocean, requiring a detour, which costs money. The evil financiers want a greater stake in the tunnel in exchange for money (i.e. all of it). It is not terribly unreasonable in the financial side of things, engineers naive about the ways of finance, yet each side needing the other to build infrastructure.
But for the “Unforeseen Volcano”, it isn’t too unreasonable either as a bit of near future science fiction. Yet, surely if they had those other technologies, they should have been able to detect a Volcano. You know, perhaps they took a submarine to survey the route before digging?
The bigger question is: Why has not something seemingly so obvious (a Transatlantic Tunnel) yet to be built, or even seriously contemplated by serious people? I know, it would have very high fixed costs unless we can somehow reduce tunnelling costs, but this is where R&D might be quite valuable, since there are lots of potential tunnels which are unbuilt due to high initial construction costs. If we could get robots to due the difficult (laborious) bits, drilling might be much, much cheaper.
David Levinson, Transportist 
I think the Mid-Atlantic Ridge is one good reason that nobody’s even contemplated doing this. Running a tunnel up to 20,000 feet below the surface across a plate boundary moving apart at an inch per year? How would one tunnel through a feature that consists of constantly seeping magma?
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The tremendous pressure at the sea floor is the biggest problem. People can generally only get down there in deep-submergence vehicles with tiny spherical crew compartments. The Woods Hole Oceanographic Institute’s Alvin (apparently originally built by General Mills(!) in Minneapolis) was upgraded in the 1970s with a titanium hull with walls two inches thick–and its crew compartment was only 6 feet in diameter. It’s got a newer 7-foot hull now.
I imagine it would make a lot more sense to have a floating tunnel anchored to the seafloor, keeping it at or less than 30 meters below the surface so that passengers wouldn’t have to worry too much about pressurization/depressurization, yet the surface weather and waves would have little effect. There would probably be some need to decompress after running several hours even at 30 meters depth, but it could be mitigated fairly well with an airliner-like pressure system, or simply by running (or stopping) at at a moderate depth for a few minutes during the ascent.
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Wikipedia’s article suggests costs between $175Billion and $12Trillion, but also suggests theoretical feasibility. One proposal suggests a floating tunnel carrying a mag-lev train.
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What would be the point? What benefit over ships and planes could possibly justify the cost? For most goods and commodities, water transportation is adequitely fast and less expensive than traditional rail (and vastly less expensive than high-speed rail) let alone rail through a 3000 mile undersea tunnel. Even for high value goods and people, airplanes would outperform every surface (or, in this case, subsurface) transportation technology over such a distance, and for a small fraction of the capital cost.
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(1) Some of the proposal for tunnels (vacuum + Maglev) are in fact faster than planes
(2) From an environmental perspective, planes burning jet fuel are problematic. Planes running on batteries are likely to be non-starters, leaving fuel of some sort (maybe biofuel) as the solution of the future.
(3) If the cost were cheaper enough (an essential caveat), it would promote more international movement, which is good for the economy.
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Surely you jest. Aside from the astronomical cost, imagine having getting stuck halfway.
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