A Hyperloop might be far more expensive than Elon Musk thinks

Elon Musk, the head of Tesla Motors and SpaceX, has unveiled his wild new idea for public transportation: The Hyperloop.

And here's the best part: Musk claims a Hyperloop would be ridiculously cheap, with tubes from San Francisco to Los Angeles costing just $6 billion or $7.5 billion (depending on whether the pods could transport cars). That's just one-tenth the cost of California's tumultuous high-speed rail project.

But is this low price tag really plausible? Even if the Hyperloop technology did work, there's good reason to think it'd be a lot pricier than Musk is letting on.

Consider some of the major factors for why California's $68 billion high-speed rail system has gone over budget. In many cases, local communities have demanded extra viaducts and tunnels added to the project that weren't strictly necessary. Other towns, meanwhile, have insisted they not be bypassed even in cases where it would be cheaper to do so. Would the Hyperloop be immune from these sorts of political pressures and tweaks?

What's more, California's high-speed rail project has had to grapple with the high costs of acquiring more than 1,100 parcels of land, often from farmers resistant to sell. The Hyperloop would try to minimize this problem by propping the whole system up on pylons, shrinking its footprint, but it can't escape the land problem entirely. As Alexis Madrigal points out, Musk's proposal seems to assume it's possible to buy up tens of thousands of acres in California for a mere $1 billion. That's awfully optimistic.

It's worth noting that overruns aren't unique to California's high-speed rail. Large infrastructure projects almost always cost far more than initial projections suggest. One Danish study (pdf) by Bent Flyvbjerg, Mette Holm and Soren Buhl looked at 250 major infrastructure projects dating back to the 1920s and found that roughly 90 percent of them went over budget — by an average of about 45 percent.

"Cost estimates used in decision-making for transport infrastructure development," the authors concluded, "are highly, systematically and significantly misleading." This seems to be true no matter what nifty new technology gets used.

Now, to be clear, this is hardly a decisive argument against the Hyperloop. The idea is undeniably intriguing. Musk says he's too busy with his day job to pursue it, but hey, if someone can make it work, good for them! What's more, even if the price tag did end up 200 percent higher than what Musk is promising, that might be still a bargain.

This is more just a general note of caution. Early cost estimates for big new transportation projects are almost always wrong — and, at least if history is anything to go by, that's not something that better technology will necessarily solve.

Further reading: For those curious, here's Musk's breakdown of the Hyperloop's costs, courtesy of Business Insider's Rob Wile: