How Maglev Trains Trade Steel Wheels for Magnetic Fields and Float Free

Japan opened its first bullet train in 1964, timed for the Tokyo Olympics. That Shinkansen reached 210 kilometers per hour and showed the world what dedicated high-speed rail could do. Today those trains routinely clear 300 kilometers per hour, matching the takeoff speed of many commercial jets. The question the TED-Ed lesson asks is whether rail can ever outpace flight itself.

Conventional high-speed trains outperform traditional passenger trains due to three deliberate design decisions. First, consider how they gain their power. Older trains run on diesel, which powers a generator that drives a motor at the wheels. High-speed trains, on the other hand, rely on energy provided by overhead wires or a third rail. Electric motors provide a lot more bang for your buck since they respond quickly, give smoother acceleration, and, most significantly, waste a lot less energy as heat. Second, consider the shape of the train itself. The long tapered noses and smooth sides of high-speed trains slice through the air rather than plowing into it, and third, the route. The rails are kept long and straight, with fewer severe turns, road crossings, and developed neighborhoods. Fewer stops means more time spent cruising at a constant speed. All of these options together can almost double the top speed of conventional trains and triple their average speed on extended distances.

Even so, such gains are constrained by something we can’t avoid: wheels grinding against steel. Friction and vibration set a fairly strict restriction. However, Maglev trains eliminate all interaction. There are two main designs that do the job. In electromagnetic suspension, a strong magnet on the train wraps around a guideway. Then it just pulls up against an iron rail, holding the car a centimeter or two above the track. The sensors are constantly changing the magnetic force to keep the gap stable. In electrodynamic suspension, a coil in the guideway generates a shifting magnetic field. That field interacts with a magnet aboard the train, creating a repulsive force that lifts the car a few centimeters higher. Both approaches keep the object centered and level, with no physical contact required.

Magnetism allows the train to move in the same way as it keeps it raised off the ground. The operators then simply reverse the polarity of each succeeding coil down the track. The front of the train is dragged to the next coil, while the back is pushed away from the one behind it. When you reverse the sequence, the train slows down again. All other things being equal, with enough straight track, the machine can already reach 430 kilometers per hour in service, with a potential ceiling of around 600. At those speeds, you could make the trip from New York to Los Angeles in under seven hours.

However, air remains the final opponent. At 300 kilometers per hour, more than 80% of a train’s energy is spent just shoving air out of the way. Some people are considering plugging the guideway into nearby vacuum tubes to decrease drag. The engineering and cost make it a pipe dream for the time being, as it is a difficult and expensive task to construct the long rights of way required to build a maglev line of any reasonable length. Things are a little more difficult in the city and out in the countryside, where the land is privately owned. Currently, just a few commercial maglev lines are operational, with the majority serving as short airport links or test routes in China, Japan, and South Korea.
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