California billionaire Elon Musk took the wraps off his vision of a futuristic Hyperloop transport system, proposing to build a solar-powered network of crash-proof capsules that would whisk people from San Francisco to Los Angeles in half an hour.

In a blog post, Musk, the chief executive of electric car maker Tesla Motors Inc, described in detail a system that, if successful, would do nothing short of revolutionising intercity transportation. But first the plan would have to overcome questions about its safety and financing.

The Hyperloop, which Musk previously described as a cross between a Concorde, rail gun and air-hockey table, would cost an estimated $6 billion to build and construction would take seven to 10 years. Eventually, according to the plan, it would jettison more than seven million people a year along one of the US West Coast’s busiest traffic corridors.

As many as 28 passengers could ride in each pod and the system could even transport vehicles, according to the 57-page design plan.

Musk, who in the past has hinted at the hopes of building such a system, proposed the Hyperloop as an alternative to a $68 billion high-speed rail project that’s a major priority of California Governor Jerry Brown. It would be safer, faster, less expensive and more convenient, Musk said in the blog post.

But not everyone is convinced the project is a good idea. Jim Powell, a co-inventor of the bullet train and director of Maglev 2000, which develops high-speed transport systems using magnetic levitation, said the system would be vulnerable to a terrorist attack or accident.

“The biggest overall problem is the idea of the low pressure tube from a terrorist standpoint,” he said after taking an initial look at Musk’s specifications. “All a terrorist driving along the highway has to do is pull over, toss a net of explosives at it, and then everyone in the tube dies,” he said.

Musk said that since the tube will be low but not zero pressure, standard air pumps could easily overcome an air leak. The transport pods could handle variable air densities.

Musk may also have neglected to factor in a few costs. Powell said that since an extensive monitoring system would be needed to keep track of the tube’s pressure, the cost of the project could double Musk’s estimate, coming closer to $12 billion.

Musk, who made his name as a PayPal founding member before going on to start SpaceX and Tesla, envisions capsules departing every 30 seconds at peak times and traversing the roughly 643 kilometres between Los Angeles and San Francisco along an elevated tube erected along the I-5 interstate highway.

The capsules ride an air cushion blasted from “skis” beneath, propelled via a magnetic linear accelerator.

The expected half-hour travel time for Hyperloop passengers compares with current travel times of an hour and 15 minutes by jet, about five-and-a-half hours by car, as well as about two hours and 40 minutes via California’s planned high-speed rail.

Other major questions remain, notably whether the California state government will ever approve the massive project, and whether any private companies are willing to step in and build it. The design remains theoretical and has yet to be tested in the field.

Musk has said he is too busy running electric car company Tesla and rocket manufacturer SpaceX to build the Hyperloop himself. He said the design plans were open-source, meaning others can build on them.

As many as 28 passengers could ride in each pod and the system could even transport vehicles

He told reporters that he could kick off the project: “I’ve come around a little bit on my thinking here. Maybe I could do the beginning bit... and then hand it over to somebody else.”

He said he would be willing to put some of his personal fortune towards the project but stressed that building the Hyperloop was a low priority for him as he continues to focus primarily on SpaceX and Tesla.

He also asked the public for help to improve the design. Corporations have resorted in the past to public assistance on their products.

In 2009, Netflix Inc awarded a cash prize to a team that succeeded in improving by 10 per cent the accuracy of its system for movie recommendations.