Trains that use magnets to levitate above the tracks might sound like something from Back to the Future, but the concept of magnetic levitation has been around for many years. Maglev trains, which use this technology, were first developed in the 1960s and many different methods have since been developed to free trains from their earthbound wheels, axles and bearings.
Maglev trains sidestep two of the limitations conventional trains have. First, the mechanical contact that conventional trains have between their wheels and the rails slows them down. Because a wheel typically weighs around a tonne, the wheel pummels away at the rail at high speed, needing regular maintenance to keep the track up to scratch.
Second, trains drive and brake themselves via this mechanical contact and therefore must carry propulsion equipment on board. This is fine at speeds of up to 400km/h (the speed of proposed Britain’s HS2 line), but aerodynamics makes going much faster very difficult. The amount of power needed increases exponentially in proportion to the vehicle speed. For example, operating at 400km/h instead of 300km/h needs nearly two and half times as much propulsion power, so at very high speeds the propulsion needed becomes impractical.