This week, Elon Musk’s tunnel-digging venture released a massive, 505-page report on its proposal to link Washington, DC and Baltimore via a high-speed transit system. It was a small but necessary step toward realizing Musk’s dream of an East Coast hyperloop, which he teased in a tweet almost two years ago.

So far, most of what we know about the Boring Company’s plans come from events staged by the company or Musk’s whimsical tweets tracking its progress. In contrast, this document, titled “Washington, DC, to Baltimore Loop Project Proposed by the Boring Company,” lays out in painstaking detail what Musk and his company would actually need to do to complete the high-speed, underground transit system. It’s a sober look at the challenges ahead.

The Boring Company proposes to dig twin, 35.3-mile tunnels approximately 30 to 90 feet below ground, bookended by two Loop stations, one in DC about a mile from Union Station, and the other in Baltimore near Camden Yards. The tunnels would be 14 feet in diameter, and lined with concrete shelves that would serve as tracks for the company’s “autonomous electric vehicles.” These battery-powered AEVs would carry passengers at speeds up to 150 mph, completing the trip in approximately 15 minutes. Today, driving a car between both cities can take an hour or more, depending on traffic.

It’s a very similar system to what Musk showed off to reporters and city officials in Los Angeles last December. That ride was incredibly bumpy, which Musk attributed to a faulty paving machine. “In the future, you can be sure it will be absolutely smooth,” he promised.

The LA tunnel was criticized for lacking ventilation or emergency exits. The Boring Company says its DC-to-Baltimore Loop would include 70 ventilation shafts, housed in nondescript gray cubes built on the surface along the route. These shafts would help passengers breath, as well as serve as emergency exits in the event of a subterranean disaster.

The company would need right-of-way permits to dig under land owned by DC, Maryland, the city of Baltimore, and the National Park Service. The Boring Company anticipates excavating around 2 million cubic yards of soil over the project construction timeline of 12 to 20 months — with a big caveat.

“Schedule variability is based on tunneling speed achieved, which is dependent upon [The Boring Company’s] technical progress prior to start of construction,” the report states. In other words, completing this massive project on schedule is entirely dependent on whether the Boring Company can follow through on its promise to speed up the tunnel boring process, which it has yet to do. The Boring Company theorizes it would need nine to 16 tunnel boring machines to get the job done.

To be sure, the Loop would not be a hyperloop, but could accommodate future hyperloops as the technology develops. “Hyperloop pods designed to fit within Loop tunnels could potentially transport passengers at speeds of up to 700 mph,” the document states, citing the speed Musk first theorized would be possible in his 2013 “Alpha” paper.

When would this happen? It’s anyone’s guess, according to the company. “The potential future use of hyperloop technology is currently unknown,” the document states. In the near term, the system would only carry a maximum 2,000 passengers each day — fewer than two full New York City subway trains.

The environmental assessment represents a scaled-back version of Musk’s original vision of a New York-Philadelphia-Baltimore-Washington hyperloop, for which he claimed to have received “verbal government approval” from the Trump administration. Later it was revealed that Musk had pitched the idea to White House advisor (and presidential son-in-law) Jared Kushner, who offered a tacit endorsement.

It sounded vague at the time, but then last year DC’s Department of Transportation issued a preliminary permit to the Boring Company to start digging at an abandoned lot in the northeast section of the city. This report is the necessary next step toward actual ground being broken on the project.

The news comes as Musk’s other tunneling projects are either making progress or running into political headwinds. Musk’s plan to build express-route tunnels around the Las Vegas Convention Center received its first approval earlier this year. But his more high-profile plan to connect O’Hare Airport to downtown Chicago is running into serious resistance. The recent election to replace outgoing Mayor Rahm Emanuel has thrown the plan into uncertainty, with incoming Mayor Lori Lightfoot calling for the tunnel project to be scrapped entirely.