Elon Musk wants to build a Hyperloop. Step 1: Explain what the heck a Hyperloop is.

Here's what a Hyperloop looks like. But what exactly is a Hyperloop? Image source: Tesla Motors.

Musk ticked that first box back in 2013, when the PayPal co-founder, SpaceX CEO, SolarCity chairman, and Tesla Motors (NASDAQ:TSLA) co-founder, CEO, and chairman released a detailed plan for construction of a $6 billion, 400-mile, 800-mile-per-hour electromagnetic subway connecting Los Angeles to San Francisco.

Step 2 was to find someone to build it -- because Musk is already wearing more than enough hats as it is and hasn't the time to head up a Hyperloop construction project on his own.

Glomming on
By 2015, two companies had emerged to take up the challenge. First, Hyperloop Transportation Technologies (HTT) volunteered to attract $100 million in venture capital out of a total $173 million cost needed to build a prototype, five-mile-long Hyperloop in California's Quay Valley. (Target date for completion: 2019.) Then, the similarly named Hyperloop Technologies set itself up with a competing plan to build a separate two-mile-long prototype in the Nevada desert.

As enthusiasm builds, though, it appears Musk has rediscovered interest in the project himself. Or maybe he just found some spare time now that he's succeeded in figuring out how to land his SpaceX rockets safely. In any case, last week, Musk's SpaceX venture announced plans to partner with an entirely different company.

And surprise! This time, it's one you can invest in.

Elon Musk's decidedly lo-res depiction of pods traveling through a Hyperloop. Image source: Tesla Motors.

The company Musk has tapped to take the lead on Hyperloop is Los Angeles-based engineering and construction specialist AECOM (NYSE:ACM). Bringing the project back to the mothership, AECOM will build its first Hyperloop test track near SpaceX HQ in Hawthorne, California.

AECOM boasts a long record of building such infrastructure projects as bridges and railways, lending real-world credibility to the whiz-bang Hyperloop project. AECOM will begin work on the mile-long track in spring of this year.

Meanwhile, SpaceX recently hosted a "Hyperloop Pod Competition," in which teams of university students submitted original designs for the pods that might one day serve as the subway cars within a Hyperloop subway system. A team from MIT won the competition, and will now proceed to build a prototype pod to test on AECOM's track.

How much will all this cost?
SpaceX hasn't revealed how much it will pay AECOM to build the Hyperloop test track. Nor do we even know, really, where the money will come from. Last week's announcement, for example, named SpaceX as AECOM's partner on Hyperloop. But the original Hyperloop proposal came from Musk in his capacity as CEO of Tesla -- whose name was stamped on the proposal.

HYPERLOOP PODs, as envisioned by TESLA MOTORS.

That said, Musk's initial proposal to build an L.A.-to-Frisco Hyperloop posited an $11.5 million-per-mile price tag. So the initial contract might not be too large, whoever pays for it.

On the other hand, HTT estimates it will spend as little as $5 million -- but perhaps as much as $20 million -- per mile to complete its five-mile Hyperloop prototype. Even that price may prove optimistic. And as The Wall Street Journal recently pointed out, a simple maglev train (no 360-degree tube surrounding it, no vacuum seal) built in Shanghai in 2004 cost $63 million per mile to build. A longer maglev under construction in Japan currently is budgeted at $250 million per mile.

The real point, though, is that whether $11.5 million, $20 million, or $250 million turns out to be the correct per-mile figure -- either way, once you multiply it by 400 miles, Hyperloop is going to be a very big deal for the company that builds it

And right now, the company that's first in line to build it is AECOM.

Now that SpaceX (or Tesla, or whoever) has a contractor ready to build Hyperloop, will investors begin to climb aboard? Image source: TESLA MOTORS.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.