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A vactrain is an exotic, as-yet-unbuilt proposal for future high-speed railroad transportation. This would entail building maglev lines through evacuated (air-less) tunnels. Though the technology is currently being investigated for development of regional networks, advocates have suggested establishing vactrains for transcontinental routes to form a global subway network. The lack of air resistance could permit vactrains to move at extremely high speeds, up to 6000-8000 km/h (4000-5000 mph or 5-6 times the speed of sound at sea level and standard conditions), according to the Discovery Channel's Extreme Engineering program "Transatlantic Tunnel".

Theoretically, vactrain tunnels could be built deep enough to pass under oceans, thus permitting very rapid intercontinental travel. Vactrains could also use gravity to assist their acceleration. If such trains went as fast as predicted, the trip between London and New York would take less than an hour, effectively supplanting aircraft as the world's fastest mode of public transportation.

Without major advances in tunnelling and other technology, however, vactrains would be prohibitively expensive. Alternatives such as elevated concrete tubes with partial vacuums have been proposed to reduce costs.


[edit] History

As far back as the late 19th century, proposals were made for a non-evacuated transatlantic tunnel linking the United States and Great Britain. This idea was highlighted in Bernhard Kellermann's 1913 novel Der Tunnel, adapted into a 1933 German film, later remade as the 1935 British film Transatlantic Tunnel.

The modern concept of a vactrain, with evacuated tubes and maglev technology, was pioneered in the 1910s by American engineer Robert Goddard, who designed detailed prototypes while a university student. His train would have travelled from Boston to New York in 12 minutes, averaging 1,000 mph (1,600 km/h). The train designs were found only after Goddard's death in 1945.

Vactrains made headlines during the 1970s when a leading advocate, Robert F. Salter of RAND, published a series of elaborate engineering articles in 1972 and again in 1978.

An interview with Robert Salter appeared in the LA TIMES (June 11, 1972). He discussed, in detail, the relative ease with which the U.S. government could build a tube shuttle system using technologies available at that time. Maglev being poorly developed at the time, he proposed steel wheels. The chamber's door to the tube would be opened, and enough air admitted behind to accelerate the train into the tube. Gravity would further accelerate the departing train down to cruise level. Rising from cruise level, the arriving train would decelerate by compressing the rarified air ahead of it, which would be vented. Pumps at the stations would make up for losses due to friction or air escaping around the edges of the train, the train itself requiring no motor. This combination of modified (shallow) gravity train and atmospheric railway propulsion would consume little energy but limit the system to subsonic speeds, hence initial routes of tens or hundreds of miles or kilometers rather than transcontinental distances were proposed.

Trains were to require no couplers, each car being directly welded or otherwise firmly connected to the next, the route calling for no more bending than the flexibility of steel could easily handle. At the end of the line the train would be moved sideways into the end chamber of the return tube. The railway would have both an inner evacuated tube and an outer tunnel. At cruise depth, the space between would have enough water to float the vacuum tube, softening the ride.

A BosWash route was laid out, with nine stations, one each in DC, Maryland, Delaware, Pennsylvania, New York, Rhode Island, Massachusetts and two in Connecticut. Commuter rail systems were mapped for the San Francisco and New York areas, the commuter version having longer, heavier trains, to be propelled less by air and more by gravity than the intercity version. The New York system was to have three lines, terminating in Babylon, Paterson, Huntington, Elizabeth, White Plains, and St George.

Salter also pointed out how such a system would help reduce the environmental damage being done to the atmosphere by aviation and surface transportation. Robert Salter called underground Very High Speed Transportation (tube shuttles) our nation's "logical next step". The plans were never taken to the next stage.

At the time these reports were published, national prestige was an issue as Japan had been operating its showcase bullet train for several years and maglev train research was hot technology. The American Planetran would establish trans-continental subway service in the United States and provide a commute from Los Angeles to New York City in one hour. The tunnel would be buried to a depth of several hundred feet in solid rock formations. Construction would make use of lasers to ensure aligment and use tungsten probes to melt through igneous rock formations. The tunnel would maintain a partial vacuum to minimize drag. A trip would average 3,000 mph (4,800 km/h) and subject passengers to forces up to 1.4 times that of gravity, requiring the use of gimballed compartments. Enormous construction costs (estimated as high as US$1 trillion) were the primary reason why Salter's proposal was never built.

Recent vactrain proposals by Frank Davidson, a founding member of the Channel Tunnel project, and Japanese engineer Yoshihiro Kyonati have tackled the transoceanic problems by floating a tube above the ocean floor, anchored with cables. The transit tube would remain at least 1,000 feet (300 m) below the ocean surface to avoid water turbulence.

[edit] Popular culture

Vactrains have occasionally appeared in science fiction novels, including the works of Arthur C. Clarke (Rescue Party, 1946), Peter F Hamilton (The Night's Dawn Trilogy), Joe Haldeman (in his novel Buying Time), Larry Niven (A World Out of Time), Robert Heinlein (Friday), Jerry Yulsman (Elleander Morning), and Jasper Fforde (the Thursday Next novels). Flash Gordon (1947) and the movie Logan's Run (1976) featured similar high-speed transport trains. The Space: 1999 TV series, featured a Lunar Vactrain. 23rd century San Francisco has one stretching across the Golden Gate Bridge in Star Trek: The Motion Picture (1979). Earlier Gene Roddenberry television productions, Genesis II and Planet Earth, featured such transport systems. A similar transportation system epitomizes the technological utopianism of the 1950s in the song "I.G.Y. (International Geophysical Year)" on Donald Fagen's 1982 album The Nightfly:

You've got to admit it—
At this point in time, that it's clear...
The future looks bright
On that train all graphite and glitter
Undersea by rail
Ninety minutes from New York to Paris
Well, by '76, we'll be A-OK!

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