"Vacuum Tube Train: A 4,000-mph magnetically levitated train could allow you to have lunch in Manhattan and still get to London in time for the theater, despite the 5-hour time difference. It’s not impossible: Norway has studied neutrally buoyant tunnels (concluding that they’re feasible, though expensive), and Shanghai is running maglev trains to its airport. But supersonic speeds require another critical step: eliminating the air—and therefore air friction—from the train’s path. A vacuum would also save the tunnel from the destructive effects of a sonic boom, which, unchecked, could potentially rip the tunnel apart." "As envisioned by Frankel and Frank Davidson, a former MIT researcher and early member of the first formal English Channel Tunnel study group, sections of neutrally buoyant tunnel submerged 150 to 300 feet beneath the surface of the Atlantic, then anchored to the seafloor–thereby avoiding the high pressures of the deep ocean. Then air would be pumped out, creating a vacuum, and alternating magnetic pulses would propel a magnetically levitated train capable of speeds up to 4,000 mph across the pond in an hour. As Frankel and Davidson say, it's doable. "We lay pipes and cables across the ocean every day," says Frankel. "The Norwegians recently investigated submerged, floating tunnels for crossing their deep fjords, and were only held back by the costs."-Carl Hoffman
SOURCE: http://www.popsci.com/scitech/article/2004-04/trans-atlantic-maglev