Elon Musk, the billionaire behind SpaceX private rockets and Tesla electric cars, has revealed his plan for the Hyperloop, a sort of love child of an air hockey table and the train from Logan's Run, that he says can shoot passengers and their cars from San Francisco to Los Angeles in 30 minutes using solar power. It's a California dream of the purest sort, and one that will literally never, never happen.

But it would be very cool if it did! In a lengthy document posted, Musk walks through his ideas for the system. We aren't engineers, so we'll trust Businessweek's description.

Inside the tubes, the pods would be mounted on thin skis made out of Inconel, a trusted alloy of SpaceX that can withstand high pressure and heat. Air gets pumped through little holes in the skis to make an air cushion, Musk says. The front of the pod would have a pair of air jet inlets—sort of like the Concorde. An electric turbo compressor would compress the air from the nose and route it to the skis and to the cabin. Magnets on the skis, plus an electromagnetic pulse, would give the pod its initial thrust; reboosting motors along the route would keep the pod moving. And: no sonic boom. With warm air inside the tubes and high tailwinds, the pods could travel at high speeds without crossing the sound barrier.

Those tubes will be mounted side-by-side on raised pillars, as at right. Those stanchions would be built to withstand seismic shock — not entirely, but to a large extent. And there you go. Travel between northern and southern California at 800 miles an hour, both literally and figuratively in the future. 

But the problems of building the Hyperloop are largely rooted in the present and past. The key problems for any transportation planners have not been finding something that can travel that distance at that speed, it's been about building the track that thing travels.

Building infrastructure in California is really, really expensive. For years, California has been trying to build high-speed rail between San Francisco and Los Angeles. As of this moment, that project is expected to cost over $70 billion and not be complete by 2029. (Musk doesn't think the high-speed rail project should be completed, for what it's worth.)

So why does Musk think Hyperloop would be cheaper? Well, in a conference call this afternoon, he pointed out that $10 billion of that cost would be land acquisition. (California land is not cheap.) By building alongside Highway 5, which runs down the Central Valley route his team plans, he anticipates that this land acquisition cost would be lower. And the costs of construction would be lower, he argues — one-tenth as much as the high-speed rail line.

It is very difficult to see how this could be the case. While raising the tube structure above ground would allow the sort of generalization of production that an on-land route would make trickier, we're still talking about a lot more material. In the conference call, Musk pointed out that the grading of the high-speed line would mean that the track would need to be built up in places, often substantially. But that's still not building a series of raised pylons at different height specifications supporting two metal tubes for the 700-mile route. The tubes would run between $2.5 and $3 billion each. Then there are the train cars, $61 million, the solar array, $210 million, the propulsion system, $691 million, and stations, $125 to $250 million. And, as the Washington Post points out, the complete bill ignores some other near-certain costs. 

The road from L.A. to San Francisco is not a straight shot. Musk's plan posits running the train "alongside the mostly very straight California Interstate 5 highway." That "mostly" is important, of course (see map at left). It would still entail the political and economic complications of land acquisition. (See The Atlantic's Alexis Madrigal on this.) If he were able to get approval for the Highway 5 route, that's still tricky. He told Businessweek that by raising the tubes he might overcome objection from some farmers in the heavily-agricultural region who have opposed the high-speed rail project.

But there are other considerations. Getting from San Francisco to the Central Valley requires a lengthy route across the hills separating the Bay Area from the middle of the state. That also includes traveling down the east side of the bay through a heavily populated area before a path east becomes clear. At the southern end of the route, it means traversing the Grapevine, the notorious stretch of mountains that marks the entry point to the Los Angeles area when coming from the north. This is not an insignificant haul — and it is not the sort of straight shot that Musk trumpets as being a solution for covering the length of the state.

Californians hate highway construction. It's not clear what that "alongside" in Musk's plan means. How far the easement stretches along the highway varies. It's not clear that the state's department of transportation would be willing to give up that space for a replacement transit system. So what if Musk built the hyperloop on risers down the middle of the highway? The result would be enormous disruptions of the highway itself — something that would meet with fierce resistance from both commuters and the various shippers that use that route. The Central Valley is the breadbasket of California. The agriculture companies that rely on Highway 5 wouldn't stand for interruptions for long.

Tube-based trains have been proposed before. In July of last year, an engineer proposed a similar system to run from New York to London using two tubes. (You'll notice that construction has not yet begun.) What Musk has going for him is a track record of success and a level of technical specificity that other similar plans can't match. Much like the Segway, which premiered to similar fanfare in 2001, and is now the province of cops and tourists.

But Musk has never been one to let practicalities interfere with his vision. On Monday's conference call with reporters, he suggested that he might just put his money where his mouth is. "I'm somewhat tempted to at least make a demonstration prototype," Musk said. "I think I'll probably end up doing that, it just won't be immediate."

In the meantime, here's the fastest way to get from San Francisco to Los Angeles — and it should be for decades to come.

All images via Tesla Motors.