Editor’s Note (06/14/18): Scientific American is re-posting the following article, originally published May 14, 2016, in light of Elon Musk’s announcement that the City of Chicago has chosen his firm, The Boring Company, to design, build, finance, operate and maintain the proposed Chicago Express Loop. The high-speed underground public transportation system would link downtown Chicago and O’Hare Airport and ferry passengers on autonomous “electric skates” traveling at up to 240 kilometers per hour. The technology needed for the system is in many ways similar to the Hyperloop tunnel–based commuter system that Musk’s SpaceX company has been promoting since 2013.

Nearly three years ago tech visionary Elon Musk outlined his vision for a new type of public transit that would be second only to teleportation in terms of speed, efficiency and “overall coolness.” The Hyperloop, as he envisioned it, would whisk commuter-filled pods hundreds of kilometers in a matter of minutes via tubes running either above- or belowground. The biggest flaw in his vision: he had no intention of actually building it.

But engineers around the world have rushed in to fill that void. Some are part of well-funded start-ups, but most are students trying to win a competition sponsored by Musk’s company SpaceX to build a functioning Hyperloop pod. The team from the Massachusetts Institute of Technology emerged earlier this year as the front-runner when it won the competition’s design phase. On Friday MIT unveiled the prototype pod it will test this summer at a 1.6-kilometer racetrack near SpaceX’s headquarters in Hawthorne, Calif.

MIT is the first among the 30 finalists to formally unveil a pod in public. Its work is the culmination of several tough engineering decisions: not just how to propel the capsule, but how to keep it on the track—and eventually make it stop. MIT chose a levitation system that uses magnets and a conducting plate, although teams were free to experiment with pods that float on an air cushion (similar to Musk’s original vision) or roll along a track on wheels. The University of Colorado Denver’s HyperLynx team has opted for a hybrid of the last two—a pod that uses wheels for traveling at less than 160 kilometers per hour and an air cushion for higher speeds.

MIT, which offered Scientific American a behind-the-scenes look at the making of its pod, opted for magnetic levitation for a number of reasons. “One of the most interesting parts of the Hyperloop is the attempt to go significantly faster than any other type of land travel,” says Greg Monahan, who is pursing a master’s in mechanical engineering and leads the team’s levitation efforts. Once a vehicle nears the speed of sound—1,236 kilometers per hour—“any type of contact with the ground or a track gets really complicated from an engineering standpoint,” he adds.

The SpaceX test track, which has yet to be built, will be a steel tube about 1.80 meters in diameter with a flat concrete floor. An aluminum surface atop the concrete will allow for magnetic levitation, and an aluminum I-beam along the center of the floor will help keep the pods from hurtling out of control “One of the challenges in creating brakes for something that is levitating is that we have to be able to stop without touching anything,” says Raghav Aggarwal, a PhD candidate in MIT’s Department of Mechanical Engineering entrusted with developing the pod’s braking system. “We are basically moving a magnet really fast next to a piece of aluminum.”

All the pods in the competition will be scaled-down versions of Musk’s Hyperloop concept: a series of passenger-carrying capsules that can operate at the speed of sound. MIT’s maglev prototype, which costs about $150,000 to build, is 2.5 meters long, weighs 250 kilograms and is expected to reach speeds up to 369 kilometers per hour  with an acceleration of 2.4 Gs. SpaceX’s decision not to require competition pods to accommodate passengers had a significant impact on the MIT design. In fact, their pod cannot simply be made bigger to fit passengers, says team captain Philippe Kirschen, a master's student in aeronautics and astronautics. “At the moment we haven’t thought about the complex questions of how you arrange passengers,” he says.

MIT became the team to beat in late January when its design placed first among more than 115 teams from 20 countries during the first phase of the SpaceX Hyperloop Pod Competition, held at Texas A&M University in College Station. Teams from Delft University of Technology in the Netherlands; the University of Wisconsin–Madison; Virginia Polytechnic Institute and State University (Virginia Tech); and the University of California, Irvine, rounded out the top five.

A number of venture capital–funded start-ups provide additional competition in the race to create a supersonic transit system through near-vacuum tubes, although they are not part of the SpaceX contest. Hyperloop One, Inc., (until recently known as Hyperloop Technologies) demonstrated its Hyperloop propulsion system in the desert about 50 kilometers outside of Las Vegas just a few days before MIT’s unveiling. The company’s 680-kilogram metal sled zipped along a 300-meter track reaching about 100 kilometers per hour in just 1.1 seconds. Hyperloop Transportation Technologies, another start-up, in March claimed to have reached an agreement with Slovakia to explore the possibility of building a high-speed tubular shuttle connecting Austria and Hungary.

California’s notorious lack of progress on plans for a high-speed railroad prompted Musk’s interest in the Hyperloop a few years ago. The entrepreneur, who has various endeavors based in the Golden State, called for a mass transit system that could help passengers commute quickly across great distances—like covering some 635 kilometers between Los Angeles and San Francisco in half an hour. Even with the competition and all the start-up money being poured into Hyperloop efforts, the required technology is likely many years away from being a feasible option for commuters. But Musk is confronting a major problem facing today’s rapidly urbanizing populations. The average travel time to work in the U.S. is just under an hour for those living in and around major metropolitan areas, according to the U.S. Census Bureau. And the total amount of time American rush-hour commuters spent stuck in traffic was about 6.9 billion hours in 2014, up from 6.4 billion in 2010, according to a report from the Texas Transportation Institute, which is part of Texas A&M.

Mass transit has become more important than ever as cities seek to cut down on congestion and pollution, says Albert Pozotrigo, executive vice president and director of construction management for M&J Engineering P.C. Whether Hyperloops could help spread populations out and simultaneously provide shorter commutes, however, depends less on engineering feats than on intangibles such as acquiring land on which to install the tubes, conforming to environmental standards and coming up with manageable cost structures for cities and passengers. “The problems that you face as an engineer are the easiest to overcome,” says Pozotrigo, whose term as president of the American Society of Civil Engineers Metropolitan Section Board of Directors ends in May.