Maglev Train.

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• Maglev Train
• Photograph by Keren Su, Corbis
• The idea of high-speed magnetically levitated trains has floated around since the early 1900s. The concept involves using magnetic fields to levitate a train above the rails, or guideways. No contact between wheels and rails means less friction, and, in theory, lower maintenance costs compared to conventional bullet trains.
• The technology has seen real-world operation, notably in German and Japanese demonstration projects, and in 2004 Shanghai launched the first commercial maglev line after two years of trials. Connecting the Shanghai airport to downtown, the Shanghai Maglev Train (pictured here) travels up to a blazing-fast 431 kilometers per hour, or about 268 miles per hour.
• But the up-front costs are steep. In 2008, Germany ditched plans for a 40-kilometer (24.9 mile) maglev project in Munich after cost estimates ballooned to more than 3 billion euros, from a previous estimate of 1.85 billion euros. But maglev isn't over and out yet. This spring, Japanese officials gave the go-aheadfor construction of a 9-trillion-yen ($111.4 billion), 320-mile (515-kilometer) maglev line between Tokyo and Osaka, much of it underground. If all goes according to plan-and maglev projects rarely do-the two cities will be connected by a 40-minute train ride by 2045.
• (Related: "On China's Roads and Rails, a Move to Smarter Transport")

• Lightweight "Dymaxion" Car
• Photograph from Hedrich Blessing Collection, Chicago History Museum/Getty Images
• A house, a map, a bathroom, and a car: Those are the widely varied applicationsthat inventor Buckminster Fuller found for his Dymaxion (dynamic maximum tension) concept. Shown here is Fuller's first Dymaxion Car, which could carry up to 11 passengers, travel up to 120 miles per hour (about 145 kilometers per hour), and average 28 miles per gallon of gasoline (a little less than 12 kilometers per liter). For comparison, the most efficient minivans in the 2012 model year are rated by the U.S. Environmental Protection Agency at only 24 miles per gallon (just over 10 kilometers per liter).
• The three-wheeled Dymaxion Car, pictured here at the 1933 Chicago World's Fair, had a steel frame and an ash wood body covered with aluminum. Painted canvas formed the roof. A Dymaxion driver ended up being killed in a crash during a demonstration of the teardrop-shaped vehicle--the apparent result of arubber-necking driver pulling alongside and hitting the vehicle. The incident spooked potential investors, and the design never made it into large-scale production.
• Still, shedding pounds has become a vital part of vehicle design in an era of automakers competing to build better, greener cars. "Light weight in vehicle design is extremely important for fuel economy and to make electric vehicles more viable," said Chris Gerdes, director of the Center for Automotive Research at Stanford University. In an email, he explained, "There is a concept known as 'mass decompounding,' meaning that as you make the car lighter, you can make the motor smaller which in turn allows you to carry fewer batteries, which reduces weight further."
• (Related: "Light Is the Bright IDEA for Transport")