Urban Transport

# Ultra-efficient 4,000 mph vacuum-tube trains – why aren't they being built?

Ultra-efficient 4,000 mph vacuum-tube trains – why aren't they being built?
Terraspan's giant, 4,000 mph (6,437 km/h) vacuum tube train, which also doubles as a superconducting power line.
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Terraspan's giant, 4,000 mph (6,437 km/h) vacuum tube train, which also doubles as a superconducting power line.

In the 1800s, when pneumatic tubes shot telegrams and small items all around buildings and sometimes small cities, the future of mass transit seemed clear: we'd be firing people around through these sealed tubes at high speeds. And it turns out we've got the technology to do that today – mag-lev rail lines remove all rolling friction from the energy equation for a train, and accelerating them through a vacuum tunnel can eliminate wind resistance to the point where it's theoretically possible to reach blistering speeds over 4,000 mph (6,437 km/h) using a fraction of the energy an airliner uses – and recapturing a lot of that energy upon deceleration. Ultra-fast, high efficiency ground transport is technologically within reach – so why isn't anybody building it?

## The next frontier of speed

Vacuum tube-based transport has a lot of things going for it. Speed, for one. Anyone who has spent time on a fast motorcycle knows that even without any wind, the air itself is a brutally powerful force working against your engine as you get up above 125 mph (200 km/h). In fact, air resistance is the number one problem to combat as speeds increase. Airliners have to fly 40,000 feet up in the air to take advantage of the reduced drag you get when the air thins out a bit. And even with this advantage, they still can't cruise much faster than 570 mph (917 km/h) without being horribly inefficient.

Take air resistance and rolling resistance away by operating in a vacuum and magnetically levitating your vehicle, and you're eliminating the biggest two hurdles to achieving extremely high speeds. And once you reach your top speed, you simply stop accelerating, apply no further energy, and coast. You lose very little speed until you reach your destination, at which point you can slow your vehicle down electromagnetically and recapture almost all the energy you put in to speed it up.

Theoretically, with the right length of vacuum tube set up, you could zoom all the way around the world in a matter of hours, nearly ten times faster than today's airliners. Operating in a vacuum, these vehicles would make almost no sound, even as they smashed through the sound barrier, because there'd be no air for them to create sonic vibrations in. With no actual points of contact or friction with the track or tube, there would be virtually no energy lost to heat dissipation.

## The vacuum-tube revolutionaries

There are no shortage of people and groups pushing for widespread adoption of vacuum tube technology as a superfast travel option – after all, with the demise of the Concorde supersonic airliner, mass global transit speeds have remained stagnant since the 1960s. Sending an e-mail from London to Beijing might be instantaneous, but the rest of the world still feels like a long way away if you have to physically travel around it.

We recently wrote about the ET3 consortium, a licensing organization that owns a number of patents in the evacuated tube transport space, Acabion's vacuum tube streamliners, and the gigantic Startram space elevator project, which would make use of the low energy requirements of the vacuum tube maglev idea to cheaply propel various objects into orbit.

Another contender with an interesting take on the technology is Terraspan, a group that wants to combine superfast transport with the creation of a new intracontinental power grid that can make much more efficient use of the cycles of power creation and usage across a large country like the United States.

Here's the plan – for step one, Terraspan would like to build a backbone network of underground vacuum tube train tunnels linking eastern Canada to western Mexico through the United States. Embedded in the train tunnel network would be a series of thick, superconducting energy cables that would form the heart of the first true continental power grid.

The benefits of a long-distance power grid are simple – you can take the energy produced by solar and wind producers in the arid central areas of America, and make it available to much more densely populated and power-hungry areas on the eastern and western coasts. You could also make more efficient use of power creation and usage cycles – energy that's created in California at off-peak times can be sent across the grid to be used in peak hour in New York.

So here's a plan that wraps up super-fast, ultra-efficient, convenient transport with smart energy usage and a tangible boost for renewable power creation schemes. Let's go, right?

## The case for the negative

Of course, if it was that simple, we'd already be blasting around the Earth at orbital speeds like they were predicting in the 1800s. Turns out there's a few serious roadblocks in the way.

Safety is no small concern when you're talking about speeds in excess of 4,000 mph (6,437 km/h). After all, we've all seen the wreckage that can be caused in a 60 mph (96 km/h) car crash. The kinds of tube tracks we're talking about here would have to stretch thousands of miles in order to reach their optimum level of benefit – that's thousands of miles of safety risks. What happens when an earthquake strikes and cracks the pressure seal or destroys the tube completely? A vehicle traveling 4,000 mph is going to eat up some serious distance in an emergency stop situation.

What's more, there's really very little precedent to show exactly what happens when a populated carriage goes from ultra high speed in a vacuum to being struck with regular air pressure. Terraspan's website details a plan to shape the trains with a sort of air wing to bring them down gently in the case of pressurization, but one can easily imagine that being battered to death at the top of the tunnel would be just as bad as crashing to your doom at the bottom of it. How can you hope to control a 4,000 mph airfoil within a tiny tube when the air pressure onset is sudden and unexpected?

The thing about maintaining a total vacuum is that one hole in your structure compromises the vacuum almost immediately. And it's not hard to dream up a dozen situations, whether natural disasters, man-made errors in judgement or acts of war or terrorism that could easily crack or break a structure like this.

Then again, let's say these safety issues can be adequately addressed. Perhaps the more pressing obstacle – at least for the time being – is a purely economical one. Mag-lev train lines themselves are exorbitantly expensive: Japan's Linimo HSST, a low-speed suburban mag-lev line, cost around US\$100 million per kilometer (0.62 miles) to build. And while China hopes to get away with only US\$18 million per kilometer when it extends its high speed Shanghai demonstration line, neither of these trains require air-tight tunnels.

Add to this the hidden cost of maintaining the vacuum (presumably by constantly pumping air particles out of thousands upon thousands of miles of vacuum tube) and you're left with a very costly proposition. And that's not to mention land acquisition – which could prove tough, as these machines move so fast that their turning radius is gigantic and route choices will be limited.

So where is vacuum-tube transport likely to go in the next few decades? It's hard to say – although it seems extremely unlikely that a cash-strapped United States or European Union member would be willing to pony up and lead the way.

Note: edited for correct physics - thanks guys, you can always rely on Gizmag commenters to keep our facts straight!

VoiceofReason
Where do I start......
It's useless unless it goes coast to coast. Distance between LA and NY is around 2400 miles. Sealing all that....good luck.
If you were going to do it. Why not two narrow diameter tubes, instead of one huge honking one. Look at the SST and the Concorde. Narrow hull. That way, even if you could lower the atmosphere by an appreciable degree it wouldn't need to be a vacuum. Which brings me to my next point. Carrying atmosphere for the passengers.
And no one has built a maglev of any appreciable distance. I'd make it a highspeed corridor on a narrow lifting body and call it good. At least that isn't a pipe dream. No pun intended.
TogetherinParis
High speeds in tubes are best attained by very long trains of tiny frontal surface area vehicles not much larger than a single person. High speeds would mean that serving meals and bathroom breaks on a train would be unnecessary, thus no isles would be necessary. Stations would have very long boarding platforms into parking lots with cabs ready and waiting, pre-positioned. A break at a station for a meal would mean a stop of you and your aero-car. IV nourishment, catheters, and anesthesia could move masses of people more efficiently over interplanetary distances. Tickets would be purchased online so stations would no longer be needed. Having everyone lie down head to foot boarding the train would maximize speed and minimize supporting infrastructure. Small diameter pipes are easier to design than large ones. Similarly light weight bridges could be used instead of massive expensive structures. Yes we could do it, but why?
Randolph Directo
Even if it was the perfect ride, @ 4000mph, what would that break neck momentum do to the human body? Does this thing also generate its own gravitational field? If so, it belongs in a discoid aircraft in space, not a tunnel under the ground.
Τριαντάφυλλος Καραγιάννης
I would put my money on a normal-air-pressure solution, running along or above highways, electric powered, fully-automated, modular and regulated to allow for easy and flexible shuttle cargo and passenger traffic with thinner infrastructures and lighter vehicles.
Monster projects are nice to admire on paper but not very practical. The ROI on this thing will be horrible unless we're talking about a mid-Europe/mid-US to Beijing sort of investment, where there's tons (pun intended :) of cargo traffic.
PS. I work for a rail company ;)
Not to mention....what happens if the train loses cabin pressure? You gonna put everyone in a pressure suit to prevent the passengers from boiling in zero atmosphere?
CaptTickTock
Good balanced overview. They will never get the construction costs back: twin 50m bore tunnels over 1000's of kilometres? And keeping a vacuum in that volume? good luck to that.
So much wasted volume, why not go for more conventional train dimensions? it's not as if you're constrained in train-length. ET3 is too far the other way for my liking, too claustrophobic. And superconducting power distribution? maybe, but you won't get the energy back either from this project.
JPAR
Would be nice to have more info on how they would generate the vacuum, and what quality would be required/maintained. Could a design be developed whereby high level vacuum on has to be maintained around & ahead of the train, easing off once the train has passed? Another thought, and possibly daft - but if you can't maintain a vacuum, how about increasing the air speed in the tube? If the tube was circular, could air speed be pushed up to 500mph+ to offset any drag at the same speed? Trains could enter & exit the main 'loop' via separate connectors so that the air speed wasn't an issue when stopping at the destination.
Doc Rock
Look,to all the naysayers.. they don't HAVE to go 4000 MPH.. the point of the article, is the same as all the 'popular mechanics' magazines of the 1950's that asked "if we have the capability of 100 miles per gallon engines, why aren't we building them?" or are you too young to remember those issues.. Oh the pain of age...;-(
mommus
it would be far cheaper and easier to build spaceplanes that fly above the atmosphere.
Bob Stuart
Removing wind resistance takes away a huge constant loss, but the energy needed for acceleration to high speeds is not affected, and not trivial. Kinetic energy increases as the square of speed, so an earthquake or other surprise could turn the train into a big explosion. @JPAR - the total skin friction in a tube is far greater than that on a train, unless the trains are extremely close together.