Faster than a speeding bullet. More powerful than a locomotive. Won’t leap tall buildings (or get airborne at all, really), but could get you from Los Angeles to San Francisco in half an hour.

That’s the promise of a mystery piece of proposed technology called the “Hyperloop,” which one of the world’s foremost transportation innovators is about to describe to the public. Could it work? One association, the American Public Transportation Association (APTA), has been speaking up about the idea in recent weeks. More details:

@elonmusk: Can you give me some basic clues? What diameter of tube so I can start designing stations & throughways? http://t.co/r53NRZ4amt

— Just A. Tinker (@John_Gardi) July 15, 2013

@John_Gardi your guess is the closest I've seen anyone guess so far. Pod diameter probably around 2m

— Elon Musk (@elonmusk) July 15, 2013

What the what?! Last year, Tesla Motors and SpaceX founder Elon Musk hinted at an audacious idea for public transportation called the “Hyperloop,” which he says wouldn’t work like a train, plane, or automobile—though he did give some of its parameters. For one, it would be low friction. For another, it would only require solar power, and finally, it would travel between San Francisco and Los Angeles in less time than it takes to fly. He’s expected to present the idea to the public in a blog post on Monday. However,  one enthusiast, self-described tinkerer John Gardi,  gained widespread attention with his tweet last month (shown above) that  Musk said was the “closest” to what he’ll be proposing.

We’re always open to new ideas, but you don’t want to hold up on the progress we’re already making on projects that are so clearly needed.

The experts weigh in: In an interview with NBC News,  APTA Vice President of Policy Art Guzzetti, welcomed new ideas such as Musk’s concept, but emphasized that whatever he suggests shouldn’t come at the cost of initiatives such as high-speed rail that are already underway. “Transportation is a huge issue for the economy,” Guzzetti told NBC News. “We’re behind on our investments, and it would certainly be a mistake to cause any delay just because new ideas are coming. There is progress. It’s not always visible, but now we’re building up a little bit of momentum. We’re always open to new ideas, but you don’t want to hold up on the progress we’re already making on projects that are so clearly needed.”

So why doesn’t this exist already? The idea many people think Musk is getting at, pneumatic tube travel, has been around for decades, but it’s yet to be built. Why is that? Another APTA official, attorney Jim LaRusch, spoke to the challenges that a project like this would create for entrepreneurs like Musk. In an interview with Popular Mechanics, LaRusch said a key reason we haven’t seen more private-sector companies try something like this is the many property rights issues they would run into—issues which would be less onerous for local governments. “It’s not really been tested,” he told the publication. “Not a lot of people have tried it without a government piece.” Musk has offered to open-source his idea, meaning it conceivably could be created by the public sector, however.

There’s a lot of interest in the Hyperloop, but one thing’s for certain—Musk doesn’t have a lot of time to devote to the endeavor. Between the legal wrangling his Tesla Motors constantly faces and the general challenges of space flight, he doesn’t exactly have a lot of free time these days.

“Obviously, I have to focus on core Tesla business and SpaceX business, and that’s more than enough,” he said in a recent Tesla conference call. “But I did commit to publishing a design and provide quite a detailed design, I think on Monday, and then invite critical feedback and see if the people can find ways to improve it.”

What do you think Musk is going to announce on Monday? Let us know your take in the comments.

Musk's Hyperloop concept is rumored to rely on pneumatic tubes, like this experimental train system invented by Alfred Ely Beach in 1867. (Wikimedia Commons/Public Domain)