Construction on the Boring Company’s newly announced underground transit link between downtown Chicago and O’Hare International Airport could start in just three to four months, Elon Musk said today. During a joint press conference with Chicago mayor Rahm Emanuel, the Boring Company CEO said that the only thing that would slow the project are the pending “regulatory and environmental approvals.”

The plan, which leaked on Wednesday ahead of a planned announcement, involves the Boring Company digging two tunnels that will connect the currently unfinished transit station underneath the Block 37 stop of the Chicago Loop system to O’Hare. Passengers will travel in high-speed pods made by Tesla in groups of up to 16 at a time (plus luggage), with pods leaving each destination as often as every 30 seconds. The pods will travel at about 150 miles per hour, fast enough to shrink the normally 40-minute ride down to just 12 minutes.

The press conference added details to that announcement, with a special focus on the economics, the logistics involved, and some of the doubts that have already been raised.

First, Musk explained why he and his tunnel boring company responded to Chicago’s open bid in the first place: the CEO said he was attracted to the city’s lack of bureaucracy. “In some places you could be [facing] upwards of 12 or 15 different separate authorities in order to get approval to do something. In Chicago, that’s a far smaller number,” Musk said. “That’s why we want to do what we think will be the first publicly useful version of the loop from the Boring Company in Chicago.”

The Boring Company has spent the last few months digging a test tunnel in California. It’s made enough progress there that, today, the company posted a video of a Model S traveling through the tunnel. During the press conference, Musk said that technical hurdles won’t hinder the Chicago project: “I feel very confident that the technologies that need to be solved here, while difficult and new, are significantly less difficult than say, what we do at SpaceX or Tesla,” he said.

As long as the company receives all the necessary approvals, Musk said, he expects to start digging from both ends of the tunnel as soon as three to four months from now. The Boring Company will use a mix of union and non-union labor, Musk said. He also said that “12 of the 15” subcontractors that will work on the project are woman, minority, or veteran-owned.

Once construction starts, Musk said he “aspirationally” expects the tunnel to be operational between 18 to 24 months later. “I would say it’s very unlikely to be more than three years” until the tunnel opens, he said. “We’re only going to open the system to the public once the safety is extremely well-proven, so even once it’s done we’ll be doing demonstration rides, but we’ll go through a rigorous safety qualification process before putting large numbers of people on board.”

While figuring out how to keep people safe in an electric sled that’s moving underground at 150 miles per hour might sound difficult, Musk said it’s “a considerably easier safety problem than vehicles operating on the highway.” Cars on the road constantly cross dangerous intersections, and drivers have to deal with the behavior of other drivers, he said. “The road problem that Tesla’s dealing with is vastly more complex than a tunnel where a vehicle’s only going in one direction on one track in a known environment.”

After the tunnel opens, Musk said the goal is to get people to and from the airport fast. He even suggested that it might be possible to perform security pre-clearance at the downtown transit station so that travelers could go “straight to [the] terminal.” He added that a deal with the Transportation Security Administration would still need to be hammered out, though.

There are already some questions about the economics of creating this tunnel link to O’Hare, but Musk seemed confident that the project will recoup its operating expenses at the least. When the issue of money came up, Musk said the transit link is “basically certain to cover its operational cost. Whether it provides a good return on capital is a separate question.”

Facing similar questions, Emanuel focused on how the financial burden was being shouldered by Musk, not the city. “He’s done both Tesla and SpaceX, and so he has a reputation, he’s also putting that on the line here. For the city, if it works? We have the tremendous opportunity” to reap the rewards of economic growth and job creation, Emanuel said. He also said the project, should it succeed, will benefit consumers because it adds another transit option. “We’re adding another choice — a competitive choice,” he said.

Beyond the skepticism about the project’s estimated cost, there are practical questions about the logistics of the project. The Boring Company’s skates haven’t been mass-produced before, and this is the company’s first attempt at a mass transit system. When the pair were asked how they respond to the doubts and criticisms that have already surfaced about the project, Emanuel let loose with a paean to Chicago’s most ambitious public works efforts:

“Were there doubters when Chicago reversed the flow of the river? Yes. Where are they today? Were there doubters when Chicago said we’re going to build the first skyscraper in America? Yeah, where are they today? Were there doubters when we said we’re going to have the tallest building in the world known before as the Sears Tower? Yes, there were doubters,” he said. “Where are they today? My view is it’s easy to be a critic or a cynic. What jobs do they produce, what economic growth do they produce?”

Musk, who regularly responds to criticism of his companies, took a less defensive tack. “I do think that there is a role for doubters. People should question things, and it shouldn’t be taken as a given that things are going to work because often things do not work,” he said. “But I think if you look at someone’s track record, or a company’s track record, and what progress has been made, it’s reasonable to extrapolate into what they would do in the future.”