Elon Musk, co-founder and chief executive officer of Tesla Inc., speaks during an unveiling event for the Tesla Model Y crossover electric vehicle in Hawthorne, California, U.S., on Friday, March 15, 2019.

Elon Musk's Boring Company is once again making a bold prediction for an ambitious project. The company says it could build a pair of high-speed underground tunnels between Baltimore and Washington, D.C., in less than two years.

The company's plan for a proposed 35-mile underground loop is outlined in a draft environmental assessment published by the U.S. Department of Transportation and the Maryland Department of Transportation.

It is not the first time the Boring Company has proposed a high-profile tunnel with an aggressive timeline. Last summer Musk, the company's CEO, signed a deal with the city of Chicago to a build a high-speed, underground transportation loop between downtown Chicago and O'Hare Airport, a distance of roughly 18 miles.

In announcing the Chicago deal last June, Musk said digging for the project could start in three to four months and be completed in 18 to 24 months, provided it moved through the regulatory approval process quickly. That hasn't happened. Almost a year later, the company's Chicago project has not received final approval.

"I would consider it dead," said Gilbert Villegas, alderman for Chicago's 34th Ward. Villegas has spent time talking with Boring Company leaders and even went for a demonstration ride in the company's test tunnel in Hawthorne, California. He said the company has a ton of smart, young engineers, but their predictions for digging and completing tunnels are too ambitious.

"On paper, a lot of these projects sound good, but [Boring Company leaders] are not being realistic with their time frames," Villegas said.

The Baltimore-to-D.C. environmental assessment says the pair of tunnels will allow modified Tesla vehicles to zip along at speeds of up to 150 miles per hour. The underground route would be between 30 and 44 feet below the surface and for the most part mirror the path of the Baltimore-Washington Parkway, one of the main routes between the two cities.

According to the assessment, "The system would operate up to 20 hours per day, with AEVs (autonomous electric vehicles) leaving each Loop Station at predetermined times. Departure intervals would be determined by various factors including station size and passenger loading time." Initially, it would be limited to 1,000 riders per day, though that could increase over time as intermediate loop stations are added.

So how long would it take to dig and finish the pair of underground tunnels, two loop stations and up to 70 ventilation shafts spread out along the route? According to the report, it could be done in 23 months.

Late last year, when Musk unveiled the 1.5-mile-long test tunnel in California, he proclaimed it would be the key to finally easing "soul crushing traffic." At an event that included giving reporters and supporters test rides, Musk described riding in the tunnel as "epic." He added, "For me it was an epiphany, like 'this thing damn well worked.'"

The public now has until early June to comment on the proposed Baltimore-to-D.C. project. After that, federal agencies, including the Federal Highway Administration, affected by the high-speed tunnel proposal would still need to approve it before the Boring Company could go forward.

Two big questions remain: How much will the Baltimore-to-D.C. loop cost, and who will pick up the bill? Neither of those issues is addressed in the environmental assessment.