Imagine being able to travel from San Francisco to Los Angeles in about 30 minutes -- in half the time that it now takes to fly the nearly 650-kilometer distance.

That is the idea announced Monday by entrepreneur Elon Musk.

The "Hyperloop" would use a large tube. Inside, capsules would float on air, traveling at more than 1,100 kilometers per hour. The air would be sucked by a powerful fan at the front and expelled at the rear.

The system is not unlike the pneumatic tubes that transport capsules stuffed with paperwork in older buildings.

Musk is the visionary behind the online payment service PayPal, electric Tesla cars and SpaceX, the private space program that successfully sent a payload to the International Space Station.

Musk said he was prompted to develop the Hyperloop design by what he says are inefficiencies in the planned high speed rail system in California. Musk said the Hyperloop could cost less than one-tenth of the $70 billion estimated for the rail plan. It would also be six times faster.

Musk says he has no plans to develop the project himself. Instead, he plans to publish the design as open source so that it can be modified or used by anyone.