Transportation pioneer Elon Musk has been known to talk big and sometimes overpromise.

But on Thursday, the Tesla chief and rocket builder took it up a notch, offering a tantalizing but so-far undocumented announcement that his tunnel-boring company had received verbal government permission to build a super-high-speed pod-and-tube transportation system, which he calls Hyperloop, to travel from Washington, D.C., to New York.

“Just received verbal govt approval for The Boring Company to build an underground NY-Phil-Balt-DC Hyperloop. NY-DC in 29 mins,” he wrote on Twitter Thursday.

Questioners on Twitter asked one of the obvious ones: Who gave the permission? Musk did not offer details.

But the Trump administration did not knock the idea down.

As envisioned by Elon Musk, a hyperloop involves a tube through which capsules carry people or cargo at high speeds, free of air resistance or friction. Wikipedia image

Asked if it had given Musk the verbal approval, a White House spokesman said: “We have had promising conversations to date, are committed to transformative infrastructure projects, and believe our greatest solutions have often come from the ingenuity and drive of the private sector.”

Musk said the system would run from “City center to city center in each case, with up to a dozen or more entry/exit elevators in each city,” according to a later tweet.

Musk’s firm intends to build the system underground using an excavation machine. The futuristic technology concept envisions transporting sealed passenger capsules in a low-pressure tube at hundreds of miles an hour.

Musk first teased the Boring Company in December, and in April hinted that his network of Hyperloops could be a nationwide phenomenon.

Building a Hyperloop above ground comes with enormous physical and regulatory challenges, which may be one reason Musk is considering an underground approach. Because Hyperloop technology involves traveling at extremely high speeds, any major turns could subject passengers to undue levels of gravity forces. That suggests that the safest, most efficient way to build the Hyperloop would be in straight lines. There’s just one problem: Above ground, you need to worry about permits and land rights. Musk’s original vision for the Hyperloop budgeted $1 billion for that alone.

Subterranean land rights may be no less complicated. But go deep enough, and at least you won’t have to worry about plowing through buildings.

Musk isn’t the only one working on Hyperloop technology. Although he has done much to popularize the concept in recent years by open-sourcing the idea, Musk has allowed other companies such as Hyperloop One to compete against each other in an effort to build the first working example.

The possible need for local permissions is another complication.

Leif Dormsjo, director of D.C.’s Department of Transportation, said “I’m completely unaware of any request to the District government to permit or review anything related to an Elon Musk project,” Dormsjo said.

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