Maglev (derived from magnetic levitation) is a new mode of transportation that lifts and propels vehicles or trains using very powerful magnets. The world's first purely maglev system, which provided origin/destination transit service to the public was opened in May 1984.  It was a low speed shuttle that ran from Birmingham International Airport terminal to the nearby railway station. Currently the most well known commercial high-speed maglev line is the Shanghai maglev line which connects Shanghai Pudong International Airport with the outskirts of central Shanghai. Maglev trains are not compatible though with conventional high-speed rail trucks and therefore a completely new infrastructure is required. The large initial investment cost for the construction of maglev infrastructure is a serious impediment to commercial use of maglev technology. 
A charged body cannot rest in stable equilibrium when placed in a pure electrostatic or magnetostatic field. Current maglev systems achieve a stable levitation using two types of maglev technology:
In EMS systems, the bottom of the vehicle is wrapped around the track like a C-shaped arm. Electromagnets are mounted in the part of the arm that is below the track. The electromagnets are attracted to the track and keep the vehicle hovering around the track. The strength of the magnetic field is continually altered by altering the current sent to electromagnets. The distance between the train and the track is approximately 15 millimeters.  However, instabilities occur with minor changes in distance between the magnets and the track. Thus, complex systems of feedback control are required to maintain stability.
In EDS systems, magnets on the train induce currents in the guideway. These currents create magnetic fields which interact with the original field of the magnets. Levitation is supported by the repulsive force between the two fields. The magnets on the train are either electromagnets or an array of permanent magnets. The advantage of EDS systems is that they are naturally stable and thus no feedback control is needed. However, EDS systems have a major disadvantage. The train must be equipped with wheels because at slow speeds the induced currents are not strong enough to support levitation.
Maglev is a fast mode of transportation. The current world speed record for maglev trains is 581 kilometers per hour, achieved in Japan in 2003.  The Shanghai maglev train holds with 431 kilometers per hour the speed record of any commercial train services.  Besides maglev, the fastest maximum operating speed of any segment of any high speed rail line is currently 350 kilometers per hour, a record first achieved by the Beijing--Tianjin Intercity Railway in August 2008.  Maglev systems are expected to fill the speed gap between high-speed rail and airplanes. The appropriate travel distance of a high speed Maglev system with maximum speed of 500 kilometers per hour is 500-1500 kilometers, in which the travel time is within 3-4 hours. In this distance, the travel time of maglev is comparable to that of airplanes.
|Table 1: Energy demand for ICE 3 and Transrapid in Watts hours per square meter of usable interior space and kilometer.  (* extrapolated value)|
Energy in maglev trains is used to accelerate, levitate and stabilize the movements of the train. Some energy is also consumed for air-conditioning, heating and lighting. However, air drag increases with the cube of the speed and therefore, at high speeds, most of the energy is needed to overcome the resistance of the air. Aircrafts take advantage of low air density at high altitudes to reduce the resistance of the air. For maglev transportation, the use of evacuated tubes has been proposed to increase the speed and efficiency of the train. . In addition, the energy consumption can be further reduced by use of regenerative braking, an energy recovery mechanism where the kinetic energy of the train can be regained when the train slows down.
Maglev is also a very cheap and efficient mode of transportation. Maglev operating costs will be only 3 cents per passenger mile and 7 cents per ton mile, compared to 15 cents per passenger mile for airplanes and 30 cents per ton mile for intercity trucks.  Guideways can last for at least 50 years with a minimal maintenance because there is no mechanical contact and wear.  At 480 kilometers per hour, maglev consumes 0.4 megajoules per passenger mile compared to 4 megajoules per passenger mile of oil fuel for a 8.5-kilometers-per-liter (20 miles-per-gallon) auto that carries 1.8 people at 96 kilometers per hour. . It is also interesting to compare the efficiency of maglev trains and conventional high-speed trains. Table 1 shows the energy consumption of the German high-speed maglev Transrapid and the German high-speed train ICE 3, both as functions of speed. Transrapid has better efficiency above 330 kilometers per hour but it is less efficient below 330 kilometers per hour.
Maglev has the potential to become a major mode of transportation. Maglev trains are the fastest mode of ground transportation and can be more efficient than cars and conventional trains at high speeds. The Shanghai maglev line proved that a commercial high-speed maglev transportation is reality. However, due to lack of new infrastructure and incompatibility with existing infrastructure large initial investment capital is required for a commercial use of maglev vehicles. Therefore, the future of maglev transportation is still uncertain.
© Stathis Ilonidis. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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