Maryland's Department of Transportation has given conditional approval to the construction of a tunnel from Baltimore to Washington, giving a boost — or hype, depending on the viewpoint — to entrepreneur Elon Musk's plan to build a super-high-speed transportation system.

The agency said Musk's the Boring Company can dig miles of tunnel under state roads to be used for the privately financed Hyperloop.

Transportation experts and engineers were left weighing what one U.S. official termed the "visionary/charlatan ratio" when it comes to Musk and his latest grand plan. Is it the beginning of something brilliant — or brilliant marketing hype?

The project will start near Fort Meade, in Anne Arundel County, said Hogan spokesman Doug Mayer. About 10 miles of tunnel will be under the state-owned portion of MD 295, the Baltimore-Washington Parkway, he said.

"It's called a utility permit. That's all they need to do the digging," Mayer said. "It's a private company, privately financed. The costs to the state will be extremely limited, if anything at all. The state has been working with them for multiple months on the permit process."

The idea of digging a long tunnel — it's roughly 35 miles from Penn Station to Union Station, though the actual route hasn't been revealed — is not far-fetched, said Mike Mooney, a tunneling professor at the Colorado School of Mines.

"This is not outside the realm. It's conceivable, certainly," Mooney said.

"Is it a big project? Sure," he added. But that's by U.S. standards, where five miles is considered the high end. "It's not a big project globally."

Technology has dramatically improved tunneling, and in vast Chinese cities, or in Qatar's capital Doha, subways, road tunnels and other projects might hit 50 or even 100 miles of digging within a five-year span, Mooney said.

Tunnel boring machines can cut through the earth, sometimes just tens of feet below the surface, leaving cement supports behind and causing no damage to the roads or buildings above, he added.

So Washington-area commuters could soon be inching along in traffic as Musk's cheekily named the Boring Company inches below at 100 or 150 feet a day, or potentially faster if Musk's promised technical upgrades to the digging process materialize

"The knock on tunneling is it's expensive. It's more expensive than surface transportation. So anything that can be done to bring innovation to drive costs down is a good thing," Mooney said.

But big questions remain on costs — to build the project and to use the system, which would work by shooting pods in vacuum-sealed tubes at high speeds.

Jose Gomez-Ibanez, a professor of Urban Planning at the Harvard Kennedy School, said he counts himself in the skeptical camp, but he does not count out Musk, who has succeeded against long odds in the past.

"I can't understand why going that fast is going to be easier in the tube than through the air," Gomez-Ibanez says. "There's a reason why trains have lost out to planes over longer distances, and that's in part because it's hard to maintain a really high quality right of way," in this case an airtight vacuum tunnel.

"You've got to respect this guy, because he's really got a record for making things that other people were skeptical about happening," Gomez-Ibanez said of Musk, the electric car pioneer and rocket builder. But the "reality of so much infrastructure" will provide a major hurdle for the Hyperloop, he said.

That could translate to costs that may be "prohibitive to the general public," said Kevin Chang, an assistant professor and transportation engineer at the University of Idaho.

And as with any mode of transportation, safety issues need to be thought through, Chang said. "If there's an unforeseen crash that occurs along the corridor, how do you mitigate the loss of life?" he said.

Still, as an engineer, he's excited by the prospect — and the freedom it could give people to live where they want.

Musk said this summer on Twitter that he had "verbal govt approval" to build a pod-and-tube transportation system, and one of his super-high-speed pod-and-tube transportation systems, known as a Hyperloop, could make the trip from New York to Washington in 29 minutes.

"I might consider working on one end of the route, and living on the other end," Chang said.

Musk also announced this summer that he had completed the first segment of his first tunnel, in Los Angeles. Another firm, Hyperloop One, is also pressing hard on the idea.

But last week's announcement left more questions than answers.

Maryland officials did not immediately have information on what is involved in the conditional approval or whether any environmental reviews are necessary for the project. Mayer referred questions on the construction timeline, costs and sources of funds to the Boring Company, which declined to answer them, relying instead on a short statement released by the state.

"The Boring Company would like to thank Maryland, Washington, D.C., and the White House Office of American Innovation for their support," the company said. In March, President Trump appointed his son-in-law, senior adviser Jared Kushner, to lead the office.

A White House spokesman said the innovation office served as "a guide to the process and helped convene meetings and calls when appropriate" to advance the broader Hyperloop project.

As for the District, a spokesman for the District Department of Transportation, Terry Owens, said: "We have had conversations with the Musk people. . . . We're trying to better understand the concept as it's been developed so far."

Correction: An earlier version of this story incorrectly described the Baltimore-Washington Parkway. It is MD 295, not Interstate 295. This version has been corrected.