MAGLEV, or magnetic levitation, is a system of transportation that suspends, guides and (usually) propels vehicles, predominantly trains, using magnetic forces. This method has the potential to be faster, quieter and smoother than wheeled mass transit systems. The technology has the potential to exceed 4000 mph (6437 km/h) if deployed in an evacuated tunnel.
Power and energy usage
Power for maglev trains is used to accelerate the train, and may be produced when the train slowed ("regenerative braking"), it is also usually used to make the train fly, and to stabilise the flight of the train, for air conditioning, heating, lighting and other miscellaneous systems. Power is also needed to force the train through the air ("air drag").
At low speeds the levitation power can be significant, but at high speeds, the total time spent levitating to travel each mile is greatly reduced, giving reduced energy use per mile, but the air drag energy increases as a square law on speed, and hence at high speed dominates. 
The following figures show how maglev trains work. 
The highest recorded speed of a maglev train is 581 km/h (361 mph), achieved in Japan in 2003, 6 km/h faster than the conventional TGV speed record. 
The term "maglev" refers not only to the vehicles, but to the railway system as well, specifically designed for magnetic levitation and propulsion. All operational implementations of maglev technology have had minimal overlap with wheeled train technology and have not been compatible with conventional rail tracks. Because they cannot share existing infrastructure, these maglev systems must be designed as complete transportation systems. The Applied Levitation SPM Maglev system is inter-operable with steel rail tracks and would permit maglev vehicles and conventional trains to operate at the same time on the same right of way.
There are three primary types of maglev technology:
a. electromagnetic suspension (EMS) uses the attractive magnetic force of a magnet beneath a rail to lift the train up.
b. electrodynamic suspension (EDS) uses a repulsive force between two magnetic fields to push the train away from the rail.
c. stabilized permanent magnet suspension (SPM) uses opposing arrays of permanent magnets to levitate the train above the rail.
Another experimental technology, which was designed, proven mathematically, peer reviewed, and patented, but is yet to be built, is the magnetodynamic suspension (MDS), which uses the attractive magnetic force of a permanent magnet array near a steel track to lift the train and hold it in place.
Maglev vs. conventional trains
Major comparative differences between the two technologies lie in backward-compatibility, rolling resistance, weight, noise, design constraints, and control systems.
Backwards Compatibility. Maglev trains currently in operation are not compatible with conventional track, and therefore require all new infrastructure for their entire route. By contrast conventional high speed trains such as the TGV are able to run at reduced speeds on existing rail infrastructure, thus reducing expenditure where new infrastructure would be particularly expensive (such as the final approaches to city terminals), or on extensions where traffic does not justify new infrastructure.
Efficiency. Due to the lack of physical contact between the track and the vehicle, maglev trains experience no rolling resistance, leaving only air resistance and electromagnetic drag, potentially improving power efficiency.
Weight. The weight of the large electromagnets in many EMS and EDS designs is a major design issue. A very strong magnetic field is required to levitate a massive train. For this reason one research path is using superconductors to improve the efficiency of the electromagnets, and the energy cost of maintaining the field.
Noise. Because the major source of noise of a maglev train comes from displaced air, maglev trains produce less noise than a conventional train at equivalent speeds. However, the psychoacoustic profile of the maglev may reduce this benefit: A study concluded that maglev noise should be rated like road traffic while conventional trains have a 5-10 dB "bonus" as they are found less annoying at the same loudness level.
Design Comparisons. Braking and overhead wire wear have caused problems for the Fastech 360 railed Shinkansen. Maglev would eliminate these issues. Magnet reliability at higher temperatures is a countervailing comparative disadvantage (see suspension types), but new alloys and manufacturing techniques have resulted in magnets that maintain their levitational force at higher temperatures.
As with many technologies, advances in linear motor design have addressed the limitations noted in early maglev systems. As linear motors must fit within or straddle their track over the full length of the train, track design for some EDS and EMS maglev systems is challenging for anything other than point-to-point services. Curves must be gentle, while switches are very long and need care to avoid breaks in current. An SPM maglev system, in which the vehicle permanently levitated over the tracks, can instantaneously switch tracks using electronic controls, with no moving parts in the track. A prototype SPM maglev train has also navigated curves with radius equal to the length of the train itself, which indciates that a full-scale train should be able to navigate curves with the same or narrower radius as a conventional train.
Control Systems. EMS Maglev needs very fast-responding control systems to maintain a stable height above the track; this needs careful design in the event of a failure in order to avoid crashing into the track during a power fluctuation. Other maglev systems do not necessarily have this problem. For example, SPM maglev systems have a stable levitation gap of several centimeters. 
Existing Maglev Systems
- Transrapid, (German maglev company)
- JR-Maglev MLX01 (Yamanashi, Japan)
- Linimo (Tobu Kyuryo Line, Japan)
- Shanghai Maglev Train (China)
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