Elon Musk Finally Reveals Underground Tunnel to Send Cars Through L.A. At 150 Miles Per Hour

On Tuesday, entrepreneur Elon Musk revealed a mile-long tunnel beneath a Los Angeles suburb that he thinks could herald a new age of traffic congestion-free cities.

Although he admits the "loop" project is in its infancy, Musk hopes his prototype tube is the first step toward networks of tubes that funnel cars through the bellies of cities across the country.

Related: Elon Musk says his high-speed Loop tunnel under L.A. is "almost done" and the public will get free rides

One day, electric vehicles will plow through the "main arteries" of such networks at 150 miles per hour, slowing only for exits that pepper the streets—10 or 20 times the number of stations you'd have for a regular subway system, Musk said at the promotional event. Cars could be equipped with retractable wheels that unfurl at their sides—aligning the vehicle with the pipe—for just $200.

On Tuesday, his tunnel—built by the Boring Co. in the city of Hawthorne for a reported $10 million—saw a car full of reporters travel at just under 50 miles per hour through the mile-long concrete tube, the BBC reported.

"The ride itself was pretty bumpy," said Matt Gutman, ABC News's chief national correspondent. The BBC's Peter Bowes agreed, writing that Musk promised passage through the network would one day be "as smooth as glass."

Although the loop system was initially expected to carry passenger pods of up to 16 people, Tuesday's demonstration saw a modified Tesla X car channel make its way through a compact white tunnel illuminated by a strip that glows blue or green.

"At first he said we're going have these tunnels and transport people in pods. Now he's saying we're going to transport them in cars, so I'm not sure even he knows how it works," The Atlantic's Alana Semuels told the BBC.

"We're obviously in the early stages here," Musk told reporters at Tuesday's promotional event. "This is a prototype. We're figuring things out. What's really important is that there is a path, finally, finally, finally…to alleviating traffic congestion in cities. If what we're saying is true, and we think it is, there is finally a solution."

Not just the seed for an inner-city solution, the tunnel is a step toward future hyperloop projects, Musk said, according to The New York Times. These mega tunnels would zip passengers or freight across much longer distances at extreme speeds with the help of a vacuum that limits friction.

Virgin Hyperloop One, for example, is actively pursuing such a system. In February, the company announced plans to build a hyperloop from Mumbai to Pune, two Indian cities separated by a 90-mile drive.

Although they may one day offer efficient travel at super-high speeds, such projects have also been criticized as fanciful, impractical and expensive.

Musk himself has plans to open versions of the Boring Co.'s loop in cities like Chicago. But some experts are skeptical of the venture. "There's an air of unreality to the project," Joseph Schwieterman, a public policy professor at DePaul University, told The New York Times back in September. "There are so many challenges that have to be overcome."