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How Maglev Trains Work


maglev test run
A magnetically levitated (maglev) train developed by Central Japan Railways Co. operates a test run on May 11, 2010 in Tsuru, Japan. Junko Kimura/Getty Images

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The evolution of mass transportation has fundamentally shifted human civilization. In the 1860s, a transcontinental railroad turned the months-long slog across America into a week-long journey. Just a few decades later, passenger automobiles made it possible to bounce across the countryside much faster than on horseback. And of course, during the World War I era, the first commercial flights began transforming our travels all over again, making coast-to-coast journeys a matter of hours. But rail trips in the U.S. aren't much faster today than they were a century ago. For engineers looking for the next big breakthrough, perhaps "magical" floating trains are just the ticket.

In the 21st century there are a few countries using powerful electromagnets to develop high-speed trains, called maglev trains. These trains float over guideways using the basic principles of magnets to replace the old steel wheel and track trains. There's no rail friction to speak of, meaning these trains can hit speeds of hundreds of miles per hour.

Yet high speed is just one major benefit of maglev trains. Because the trains rarely (if ever) touch the track, there's far less noise and vibration than typical, earth-shaking trains. Less vibration and friction results in fewer mechanical breakdowns, meaning that maglev trains are less likely to encounter weather-related delays.

The first patents for magnetic levitation (maglev) technologies were filed by French-born American engineer Emile Bachelet all the way back in the early 1910s. Even before that, in 1904, American professor and inventor Robert Goddard had written a paper outlining the idea of maglev levitation [source: Witschge]. It wasn't long before engineers began planning train systems based on this futuristic vision. Soon, they believed, passengers would board magnetically propelled cars and zip from place to place at high speed, and without many of the maintenance and safety concerns of traditional railroads.

The big difference between a maglev train and a conventional train is that maglev trains do not have an engine — at least not the kind of engine used to pull typical train cars along steel tracks. The engine for maglev trains is rather inconspicuous. Instead of using fossil fuels, the magnetic field created by the electrified coils in the guideway walls and the track combine to propel the train.

If you've ever played with magnets, you know that opposite poles attract and like poles repel each other. This is the basic principle behind electromagnetic propulsion. Electromagnets are similar to other magnets in that they attract metal objects, but the magnetic pull is temporary. You can easily create a small electromagnet yourself by connecting the ends of a copper wire to the positive and negative ends of an AA, C or D-cell battery. This creates a small magnetic field. If you disconnect either end of the wire from the battery, the magnetic field is taken away.

The magnetic field created in this wire-and-battery experiment is the simple idea behind a maglev train rail system. There are three components to this system:

  1. A large electrical power source
  2. Metal coils lining a guideway or track
  3. Large guidance magnets attached to the underside of the train

We'll look at the track next.

The Maglev Track

The Maglev track allows the train to float above the track through the use of repelling magnets. Learn about the Maglev track and see a diagram of a Magelev track.
The Maglev track allows the train to float above the track through the use of repelling magnets. Learn about the Maglev track and see a diagram of a Magelev track.
HowStuffWorks

The magnetized coil running along the track, called a guideway, repels the large magnets on the train's undercarriage, allowing the train to levitate between 0.39 and 3.93 inches (1 to 10 centimeters) above the guideway [source: Boslaugh]. Once the train is levitated, power is supplied to the coils within the guideway walls to create a unique system of magnetic fields that pull and push the train along the guideway. The electric current supplied to the coils in the guideway walls is constantly alternating to change the polarity of the magnetized coils. This change in polarity causes the magnetic field in front of the train to pull the vehicle forward, while the magnetic field behind the train adds more forward thrust.

Maglev trains float on a cushion of air, eliminating friction. This lack of friction and the trains' aerodynamic designs allow these trains to reach unprecedented ground transportation speeds of more than 310 mph (500 kph), or twice as fast as Amtrak's fastest commuter train [source: Boslaugh]. In comparison, a Boeing-777 commercial airplane used for long-range flights can reach a top speed of about 562 mph (905 kph). Developers say that maglev trains will eventually link cities that are up to 1,000 miles (1,609 kilometers) apart. At 310 mph, you could travel from Paris to Rome in just over two hours.

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Some maglev trains are capable of even greater speeds. In October 2016, a Japan Railway maglev bullet train blazed all the way to 374 mph (601 kph) during a short run. Those kinds of speeds give engineers hope that the technology will prove useful for routes that are hundreds of miles long.

Germany and Japan both have developed maglev train technology, and tested prototypes of their trains. Although based on similar concepts, the German and Japanese trains have distinct differences. In Germany, engineers developed an electromagnetic suspension (EMS) system, called Transrapid. In this system, the bottom of the train wraps around a steel guideway. Electromagnets attached to the train's undercarriage are directed up toward the guideway, which levitates the train about 1/3 of an inch (1 centimeter) above the guideway and keeps the train levitated even when it's not moving. Other guidance magnets embedded in the train's body keep it stable during travel. Germany demonstrated that the Transrapid maglev train can reach 300 mph with people onboard. However, after an accident in 2006 (see sidebar) and huge cost overruns on a proposed Munich Central Station-to-airport route, plans to build a maglev train in Germany were scrapped in 2008 [source: DW]. Since then, Asia has become the hub for maglev activity.

Electrodynamic Suspension (EDS)

Above is an image of the guideway for the Yamanashi maglev test line in Japan.
Above is an image of the guideway for the Yamanashi maglev test line in Japan.
Photos courtesy Railway Technical Research Institute

Japanese engineers have developed a competing version of maglev trains that use an electrodynamic suspension (EDS) system, which is based on the repelling force of magnets. The key difference between Japanese and German maglev train technology is that the Japanese trains use super-cooled, superconducting electromagnets. This kind of electromagnet can conduct electricity even after the power supply has been shut off. In the EMS system, which uses standard electromagnets, the coils only conduct electricity when a power supply is present. By chilling the coils at frigid temperatures, Japan's system saves energy. However, the cryogenic system used to cool the coils can be expensive and add significantly to construction and maintenance costs.

Another difference between the systems is that the Japanese trains levitate nearly 4 inches (10 centimeters) above the guideway. One potential drawback in using the EDS system is that maglev trains must roll on rubber tires until they reach a liftoff speed of about 93 mph (150 kph). Japanese engineers say the wheels are an advantage if a power failure caused a shutdown of the system. Also, passengers with pacemakers would have to be shielded from the magnetic fields generated by the superconducting electromagnets.

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The Inductrack is a newer type of EDS that uses permanent room-temperature magnets to produce the magnetic fields instead of powered electromagnets or cooled superconducting magnets. Inductrack uses a power source to accelerate the train only until it begins to levitate. If the power fails, the train can slow down gradually and stop on its auxillary wheels.

The track is actually an array of electrically shorted circuits containing insulated wire. In one design, these circuits are aligned like rungs in a ladder. As the train moves, a magnetic field repels the magnets, causing the train to levitate.

There are currently three Inductrack designs: Inductrack I, Inductrack II, and Inductrack III. Inductrack I is designed for high speeds, while Inductrack II is suited for slow speeds. Inductrack III is specifically designed for very heavy cargo loads moved at slow speeds. Inductrack trains could levitate higher with greater stability. As long as it's moving a few miles per hour, an Inductrack train will levitate nearly an inch (2.54 centimeters) above the track. A greater gap above the track means that the train would not require complex sensing systems to maintain stability.

Permanent magnets had not been used before because scientists thought that they would not create enough levitating force. The Inductrack design bypasses this problem by arranging the magnets in a Halbach array. The magnets are configured so that the intensity of the magnetic field concentrates above the array instead of below it. They are made from a newer material comprising a neodymium-iron-boron alloy, which generates a higher magnetic field. The Inductrack II design incorporates two Halbach arrays to generate a stronger magnetic field at lower speeds.

Notably, the passive magnetic levitation concept is a core feature of proposed hyperloop transportation systems, which is essentially an Inductrack-style train that blasts through a sealed tube that encases the entire track. It's possible that hyperloops may become the approach of choice, in part because they dodge the issue of air resistance in the way the regular maglevs cannot, and thus, should be able to achieve supersonic speeds. Some say that a hyperloop might cost even less than a traditional high-speed rail line.

But whereas maglev trains are already a proven technology with years of operational history, no one has yet built a commercial hyperloop anywhere in the world [source: Davies].

Maglev Technology In Use

A Transrapid train at the Emsland, Germany test facility.
A Transrapid train at the Emsland, Germany test facility.

While maglev transportation was first proposed more than a century ago, the first commercial maglev train didn't become a reality until 1984, when a low-speed maglev shuttle became operational between the United Kingdom's Birmingham International railway station and an airport terminal of Birmingham International Airport. Since then, various maglev projects have started, stalled, or been outright abandoned. However, there are currently six commercial maglev lines, and they're all located in South Korea, Japan and China.

The fact that maglev systems are fast, smooth and efficient doesn't change one crippling fact – these systems are incredibly expensive to build. U.S. cities from Los Angeles to Pittsburgh to San Diego had maglev line plans in the works, but the expense of building a maglev transportation system (roughly $50 million to $200 million per mile) has been prohibitive and eventually killed off most of the proposed projects. Some critics lambast maglev projects as costs perhaps five times as much as traditional rail lines. But proponents point out that the cost of operating these trains is, in some cases, up to 70 percent less than with old-school train technology [sources: Hall, Hidekazu and Nobuo].

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It doesn't help that some high-profile projects have flopped. The administration at Old Dominion University in Virginia had hoped to have a super shuttle zipping students back and forth across campus starting back in the fall semester of 2002, but the train did a few test runs and never really approached the 40 mph (64 kph) speeds it promised. The train stations were finally deconstructed in 2010 but parts of the elevated track system still stands, a testament to a $16 million failure [source: Kidd].

But other projects persist. One ambitious group wants to build a 40-mile (64-kilometer) stretch from Washington D.C. to Baltimore, and the idea has plenty of proponents, but the project is expected to cost up to $15 billion. The concept's exorbitant price tag might be laughable just about anywhere else in the world, but this region's soul-crushing gridlock and limited space means city planners and engineers need an innovative solution, and a super-fast maglev system might be the best option. A key selling point – an expansion to this project could connect to Washington to New York city and cut travel times to just 60 minutes, a speedy commute that could transform commerce and travel in the Northeast [sources: Lazo, Northeast Maglev].

In Asia, though, the maglev boom is essentially already underway. Japan is working feverishly on a Tokyo-to-Osaka route that may open by 2037. When it's complete, the train will slash the nearly three hour trip to just 67 minutes [source: Reuters].

China is seriously considering dozens of potential maglev routes, all of them in congested areas that require high-capacity mass transportation. These won't be high-speed trains. Instead, they'll move lots of people over shorter distances at lower speeds. Nevertheless, China manufactures all of its own maglev technologies and is about to unveil a third-generation commercial maglev line with a top speed of around 125 mph (201 kph) and – unlike previous versions – is completely driverless, relying instead on computer sensors for acceleration and braking (The country already has some maglev trains in operation but they need a driver.) [source: Wong].

It's impossible to know exactly how maglevs will figure into the future of human transportation. Advances in self-driving cars and air travel may complicate the deployment of maglev lines. If the hyperloop industry manages to generate momentum, it could disrupt all sorts of transportation systems. And some engineers suspect that even flying cars, though incredibly pricey, might trump rail systems in the future because they don't need massive infrastructure projects to get off the ground.

Perhaps in just a decade or two, nations around the world will have come to a verdict on maglev trains. Maybe they'll become a linchpin of high-speed travel, or simply pet projects that serve just fragments of certain populations in crowded urban area. Or perhaps they'll simply fade into history, a nearly magical form of levitation technology that just never really took off.

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More Great Links

Sources

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