Elon Musk's Boring Company is nearing completion of its first tunnel near SpaceX headquarters. In a Thursday evening Instagram post, the mogul showed off a fly-through video:

"Pending final regulatory approvals, we will be offering free rides to the public in a few months," Musk wrote. "As mentioned in prior posts, once fully operational (demo system rides will be free), the system will always give priority to pods for pedestrians & cyclists for less than the cost of a bus ticket."

It's not clear how far Musk plans to take his tunneling project. He certainly has an ambitious vision. In a March tweet, he wrote that "Boring Co urban loop system would have 1000’s of small stations the size of a single parking space that take you very close to your destination & blend seamlessly into the fabric of a city, rather than a small number of big stations like a subway."

Musk's team has also done some preliminary work on the electric sled that would carry people around in the system—he showed off a prototype of the technology last year.

In addition to tunneling in Los Angeles, Musk has gotten permission to dig a 10-mile tunnel along the route of the Baltimore-Washington Parkway in Maryland and to dig up a parking lot in Washington DC—supposedly in preparation for a massive New York-to-DC Hyperloop that could take people between the two cities in under 30 minutes. The company is also working on a proposal for a tunnel that would carry passengers from downtown Chicago to the O'Hare airport.

At the same time, other details of Musk's vision are maddeningly vague. Initially, Musk envisioned the system as a faster way to move cars around the city. More recently, he has indicated that the system would give priority to pedestrians and cyclists, making it sound more like a conventional subway.

But it's not obvious that tunneling technology, per se, is the big obstacle to building more extensive subway networks. It was relatively easy to get permission to tunnel under the Baltimore-Maryland Parkway because that land was owned by the state of Maryland and didn't have a lot underground. But an urban subway system needs the right to tunnel under thousands of pieces of privately owned land. It needs to avoid damaging underground pipes and wires, and stations need access to the surface.

The planning, negotiations, environmental reviews, and litigation required to get all the necessary permissions account for a large share of the costs of any ambitious transportation project. Musk undeniably has some experience negotiating with government agencies—after all, he convinced NASA to take a chance on SpaceX rockets. But so far there hasn't been much sign that he's actually laying the groundwork that would be necessary to build a functional transportation network in California, Maryland, Illinois, or anywhere else.

Correction: I misread an LA Times story and got two tunnels confused. As a result, I described this as a 2.7-mile tunnel in West Los Angeles, when in fact that's a different tunnel that has been proposed but hasn't been constructed yet. This tunnel, in contrast, is located around SpaceX headquarters in Hawthorne. Musk hasn't revealed its exact length, but the company submitted a proposal for a 2-mile tunnel at the site last year. We regret the error.