Billionaire entrepreneur Elon Musk unveiled new details today (Aug. 12) about his proposed "Hyperloop" project, a futuristic, super-fast transportation system that could ferry passengers between Los Angeles and San Francisco in about 30 minutes.
The , which Musk has described as a "cross between a Concorde, a rail gun and an air hockey table," could travel at a blistering pace of 760 mph or so (1,220 km/h).
Moving people at such high speeds could ease congestion problems along intercity highways and could provide more efficient, affordable and "greener" alternatives to bus, train or air travel, Musk said. 
But while ultra high-speed transportation has myriad benefits, developing these systems also comes with significant technical and political challenges, said James Powell, an American physicist and co-inventor of the , high-speed trains that are propelled by powerful magnets.
For one, traveling at such high speeds will require the Hyperloop to move along a track that avoids turns and hills.
"It's doable, but you have to build a track or tunnel that's very straight," Powell told LiveScience. "At that speed, the track has to be straight and flat, to avoid bumpiness. When you're going 600 miles per hour, you can't really go around curves, and you'd have to be very flat, because without causing excessive G-forces, you probably wouldn't be able to adjust to changing elevations rapidly."
The Hyperloop project is designed to accelerate 6.5-feet-wide (2 meters) pods through a low-pressure tube. The Hyperloop pods would ride on a cushion of air, rather than on traditional rails, which would enable them to .
Superconducting Maglev (short for magnetic levitation) vehicles, which Powell developed together with Gordon Danby, use magnets to create lift and thrust, and can travel fast because they do not have to contend with friction from wheels and axles on a rail. Maglev trains are designed to travel at around 300 mph (483 km/h), but in December 2003, aclocked a top speed of 361 mph (581 km/h). Musk's concept of the Hyperloop would transport passengers at double the speed of Maglev trains.
Musk said the Hyperloop is a more efficient and cost-effective alternative to the California High-Speed Rail project, a nearly $70 billion system planned to link most of the major cities in California, including Sacramento, San Francisco, Los Angeles and San Diego.
"When the California 'high speed' rail was approved, I was quite disappointed, as I know many others were too," Musk wrote in a blog post today about the Hyperloop project. "How could it be that the home of Silicon Valley and [the Jet Propulsion Laboratory] doing incredible things like indexing all the world's knowledge and putting would build a bullet train that is both one of the most expensive per mile and one of the slowest in the world?"
Musk said any major investments in transportation should have equally major returns, and should be pursued only if they do, in fact, present a better alterative to flying or driving.