Vacuum tube rail

A vacuum tube rail is a proposed design for very-high-speed rail transportation. It is a maglev (magnetic levitation) line using partly evacuated tubes or tunnels. Reduced air resistance could permit a train to travel at very high (hypersonic) speeds with relatively little power—up to 6,400–8,000 km/h (4,000–5,000 mph). (link)

A vacuum tube rail is hard to transport heavy freight or passengers, because a lot of technical problems have not been solved yet.