The future of transport: No loopy idea

Elon Musk, electric-car entrepreneur and proponent of private colonies on Mars, now plans to redesign the railway

HALF a century after they were pioneered in France and Japan, could high-speed trains be coming to America? Last year California’s legislators gave $7.7 billion to a project called California High Speed Rail (CHSR). If and when it is completed it will connect San Francisco to Los Angeles, with branch lines to Sacramento and San Diego. This first slice of what the budget suggests will eventually be a bill for $68 billion will be used to construct 210km (130 miles) of track between Fresno and Bakersfield. But just because the money has been allocated does not mean the line will actually get built. It is far from universally popular. Besides the estimated price (and even this is probably a shot in the dark, for big infrastructure projects are hardly known for coming in on budget), it may not even be that fast. The short distances between many of its stations mean trains will rarely be able to reach their planned top speed of 350kph.

Fortunately, California is home to many clever people. One of them is Elon Musk, the hyperactive boss of Tesla Motors, an electric-car company, and SpaceX, a rocketry business (he also sits on the board of Solar City, a solar-energy firm). There is nothing Mr Musk likes more than revolutionising high-tech industries. And he thinks he has come up with a better way to get California moving than a standard high-speed train. Mr Musk—who is as good at PR as he is at engineering—first mentioned his idea, called Hyperloop, last year, prompting excited speculation about what he might have had in mind.

Mr Musk’s atmospheric caper

On August 12th, in a short document published on the websites of Tesla and SpaceX, all was revealed. Essentially, Mr Musk proposes to revive an old science-fiction idea called the vac-train (short for “vacuum train”), albeit with a few important tweaks. The Hyperloop would carry passengers across California at more than 1,200kph—faster than a jet airliner—allowing them to zoom between San Francisco and Los Angeles in little over half an hour, compared with more than two-and-a-half hours for CHSR. It would be solar-powered, would take less land than a high-speed railway, and would be cheaper to boot. Mr Musk’s notional budget is around $6 billion, less than a tenth of what the high-speed train is supposed to cost.

Vac-trains, as first described in the 1910s by Robert Goddard (better known as a pioneer of rocketry), would send rolling stock (or hovering stock, perhaps) hurtling through hermetically sealed tubes from which the air has been evacuated. The trains would thus encounter no drag, and be able to reach immense speeds. Goddard reckoned his design—which also proposed magnetic levitation instead of wheels—was good for about 1,600 kph.

This and other designs for transporter tubes inspired much futuristic art, as the illustration above suggests. But none was ever built because maintaining a vacuum in a long tunnel is difficult. Pumps must work exponentially harder as the pressure falls, to evacuate the few air molecules that remain. And even a small leak would scupper a full-fledged vac-train, which relies on no air at all being able to build up in front of it, and thus slow it down. For that reason, the Hyperloop is not actually a true vac-train. Instead, Mr Musk plans to remove sufficient air from the tubes to give them a pressure roughly a sixth of that on the surface of his beloved Mars, or a thousandth of that on Earth at sea level. This would keep the air resistance low enough to deal with in other ways.

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