What started as a joke has turned into a real-life prototype. Elon Musk japed that he'd dig tunnels under Los Angeles to avoid traffic, and on Tuesday his Boring Company opened its first prototype tunnel in LA. The entrepreneur behind Tesla and SpaceX also provided more details on how the system works.

Musk started The Boring Company as a solution to traffic and congested cities. Machines dig tunnels to fit a vehicle, and an elevator shaft drops them down. From there, the car deploys tracking wheels that rub against the walls to guide it along the tunnel. For now, it's unclear how a vehicle will be outfitted with the tracking wheels or how it will deploy them. Musk tweeted that the retractable wheel gear "turns a car into a rail-guided train & back again." The rails are actually the sides of the tunnel and the cars remain cars.

When completely realized, the vehicles could move at speeds in excess of 150 mph. CNN Business, which was present at the opening event, said trial tests had the car moving at speeds of 35 mph in the 1.14-mile long tunnel, but the concept worked. The tunnel system is called the Loop.

The prototype featured a Tesla Model X fitted with the proper retractable running gear to work in the tunnel, but dedicated Boring Loop vehicles will circulate continuously to pick up pedestrians and cyclists, according to tweets from Musk. Additionally, Musk said the system can be applied to any self-driving electric car, not just Teslas. Privately owned vehicles outfitted with the deployable tracking wheels would also be allowed to use the Boring Loops.

The first test tunnel runs from a parking lot in Hawthorne, California, to the SpaceX headquarters. After two years or development, the tunnel reportedly cost $10 million to develop and construct as a proof-of-concept for other projects Musk plans across the United States. The Boring Company was tapped to build a Boring Loop in Chicago from downtown to O'Hare airport, a second California tunnel, and a Loop in Washington state. So far, work hasn't progressed on the Chicago or Washington Loops, and the company ditched the idea for a second California tunnel for now after a lawsuit from neighborhood groups.

The Boring Company concept

The Boring Company concept

However, eventually, Musk wants a full system of underground tunnels in LA.

We're a long way from any sort of massive underground system as red tape and regulatory hurdles stand in the way, but for now, we know the system works, at least at 35 mph. Maybe Musk is onto something after all.