Mass Transit is by no means a new idea - railroads have been around since 1829, and we've been riding trains ever since. Although new technology allows us to ride faster and more comfortably, the basic idea is the same: a locomotive of some sort pulls or pushes a string of cars along a metal railway. But now, after over one hundred years of faithful service, the old railroad systems are being retired. A new system is making its mark on the world, and its name is MagLev.
MagLev, or magnetic levitation, trains are the newest and brightest form of Mass Transit. The technology has already been implemented in Germany and Japan, and although it was researched and proposed, it never really took hold in the United States. The German version of the MagLev train, called Transrapid, opened in 1989, the same year as the Japanese MLU002 began running. The little-used American version is called Inductrack. Each of these trains uses a different type of MagLev technology.
Before going into that, however, one should understand the fundamental concepts behind MagLev trains. A MagLev train is called that for a very good reason - the train cars use gigantic magnets to hover above their tracks, decreasing the negative impact friction has on a train's speed and allowing the cars to achieve much greater speeds than normal railroad cars.
There are two different types of magnetic levitation used in MagLev trains - electrodynamic suspension (EDS) and electromagnetic suspension (EMS). Judging by name alone, EDS and EMS don't sound very much different, but in reality they are as opposite as night and day.
EDS uses the repulsive force between superconducting magnets mounted in the vehicle and other conducting magnets in its "U"-shaped guideway to keep the vehicle levitating. EDS technology is more expensive than other methods, since it requires that permanent magnets be installed in the track and the vehicle; still, it is safer, since guide wheels can be installed in case something goes wrong, and vertical, roll, pitch, lateral, and yaw motions are all more stable and easily controlled in an EDS train. The Japanese MLU002 is an example of EDS technology in action. The Japanese chose it for its safety, reduced energy losses, and lighter vehicles, and were able to use cheaper materials to reduce costs.
EMS, on the other hand, utilizes the attractive force of magnets by wrapping the bottom of the vehicle around the track and mounting magnets in the part of the vehicle that's below the track. This way, the electromagnets underneath are attracted to the track, made of a ferromagnetic substance (i.e., a regular magnet made of something similar to iron), and just enough energy is put into the electromagnets to keep the vehicle hovering around the track.
A MagLev train using the EMS system pulls itself along the track with a linear synchronous motor (LSM), which, in simple terms, uses the electromagnetic currents in the vehicle to attract it to the track ahead of it, so that the vehicle is drawn further along the track. The speed is adjusted by changing the frequency of the electromagnetic fields pulling the vehicle.
The drawback to using EMS technology is that vertical, roll, and pitch motions must be controlled by other electromagnets outside the vehicle. Also, EMS trains are slightly less safe, since they have no guide wheels to catch the vehicle in the event of a malfunction or power failure. However, they are cheaper, since the track need only be a sizeable chunk of ferromagnetic material. One example of a MagLev train using EMS technology is the German Transrapid, choosing EMS for its rapid development and certification time. The trains are designed to operate at speeds of 250 to 310 mph, and although the design is more complicated and expensive, it consumes 30% less energy than other MagLev trains and can carry up to 1,060 passengers in a ten-section set.
There is one final type of magnetic levitation technology that is used solely in the American version of MagLev, known as Inductrack. Inductrack employs what is known as a Halbach Array, or a set of large, powerful bar magnets arranged very carefully, so that an enhanced magnetic field is generated below the array, but none above it. Also, the array of magnets acts like a coiled spring - as the distance between the array and the track decreases, the levitating force increases exponentially, so that no matter how heavy the cars are, they will still hover above the track. Halbach Arrays are mounted on the bottom of Inductrack vehicles, and electromagnetic coils placed in the track help generate even more magnetic force. Inductrack trains are inherently stable and, since they use permanent magnets, they require very little power. As stated earlier, the American Inductrack is the only type of MagLev train that uses Halbach Arrays, and although it seems like a very good idea, Inductrack is not very prevalent in America.
To compare mass transit to air travel, railroad cars are like propeller planes, and MagLev trains are like Boeing jets. MagLev trains are faster, vastly more efficient, definitely more environment-friendly, and safer than traditional trains, airplanes, and automobiles. The newest hit in mass transit is here, and its name is MagLev.
Figure 1 Wheelset degrees of freedom.
