Maglev (derived from magnetic levitation) is a method of propulsion that uses magnetic levitation to propel vehicles with magnets rather than with wheels, axles and bearings. With maglev, a vehicle is levitated a short distance away from a guide way using magnets to create both lift and thrust. High-speed maglev trains promise dramatic improvements for human travel if widespread adoption occurs.
Maglev trains move more smoothly and somewhat more quietly than wheeled mass transit systems. Their non-reliance on traction and friction means that acceleration and deceleration can surpass that of wheeled transports, and they are unaffected by weather.
The power needed for levitation is typically not a large percentage of the overall energy consumption; most of the power is used to overcome air resistance (drag), as with any other high-speed form of transport. Although conventional wheeled transportation can travel very quickly, a maglev system allows routine use of higher top speeds than does conventional rail, and it is this type which holds the speed record for rail transportation. Vacuum tube train systems might hypothetically allow maglev trains to attain speeds in a different order of magnitude, but no such tracks have ever been built.
Compared to conventional wheeled trains, differences in construction affect the economics of maglev trains. In wheeled trains at very high speeds, the wear and tear from friction along with the hammer effect from wheels on rails accelerates equipment deterioration and prevents mechanically based train systems from routinely achieving higher speeds. Conversely, maglev tracks have historically been found to be much more expensive to construct, but require less maintenance and have lower ongoing costs.
Despite decades-long research and development, there are presently only two commercial maglev transport systems in operation, with two others under construction. In April 2004, Shanghai began commercial operations of the high-speed Transrapid system. In March 2005, Japan began operation of the relatively low-speed HSST "Linimo" line in time for the 2005 World Expo. In its first three months, the Linimo line carried over 10 million passengers. South Korea and the People's Republic of China are both building low-speed maglev lines of their own design, one in Beijing and the other at Seoul's Incheon Airport. Many maglev projects are controversial, and the technological potential, adoption prospects and economics of maglev systems have often been hotly debated. The Shanghai system has been accused of being a white elephant by critics and opponents.