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

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!