A vactrain (or vacuum tube train) is a proposed, as-yet-unbuilt
design for future high-speed railroad transportation. It is a
maglev line run through evacuated (air-less) or partly evacuated
tubes or tunnels. The lack of air resistance could permit
vactrains to use little power and to move at extremely high
speeds, up to 4000–5000 mph (6400–8000 km/h, 2 km/s), or 5–6
times the speed of sound (Mach 1) at sea level and standard
conditions. Though the technology is currently being
investigated for development of regional networks, advocates
have suggested establishing vactrains for transcontinental
routes to form a global network. Vactrain tunnels could permit
very rapid intercontinental travel. Vactrains could 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, supplanting aircraft as the world's fastest mode
of public transportation. Travel through evacuated tubes allows
supersonic speed without the penalty of so