Elon Musk made a splash almost two years ago when he declared he had “verbal govt approval” to build an underground “Hyperloop” project that would get people from Washington to New York City in 29 minutes, cutting through Baltimore and Philadelphia along the way.

Hyperloop passengers would shoot through vacuum tubes in pods traveling more than 600 miles per hour, according to Musk’s tunneling venture, the Boring Company.

But the electric-car pioneer’s latest take on that plan, detailed late Wednesday in a report considering environmental impacts, is to build two 35-mile tunnels from Washington to Baltimore that would carry autonomous Teslas or their corporate cousins at 150 miles per hour, on rubber tires, getting from city to city in about 15 minutes.

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The 505-page environmental assessment from federal and Maryland state transportation officials shows how Musk’s original vision has, depending on one’s perspective, either shrunk wildly or begun to sprout in intriguing ways. Unanswered in the report, however, are questions on the cost, safety and practicality of the effort.

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Among a host of federal, state and local issues yet to be resolved is how Musk would compensate the National Park Service for building under the Baltimore-Washington Parkway. The current proposal calls for a “land exchange,” in which Musk’s company would give the Park Service land “of approximately equal value” in exchange for an easement giving it the right to build the tunnels.

The project, while being proposed by the Boring Company, is formally sponsored by the Maryland State Highway Administration, which worked with the Federal Highway Administration in preparing the draft environmental assessment. “Technical information forming the basis” of the assessment “was developed and prepared by” the company, according to the report. There will be a 45-day public comment period.

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Federal and state officials will review the public responses, and federal highway officials will determine if the impacts are considered “significant” enough to warrant a more extensive environmental review under federal law. Maryland transportation department spokeswoman Erin Henson declined to characterize the potential environmental impacts or project benefits.

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The report on what is now called simply “Loop” is notable for what it says the project will not do. Despite the early talk of transformation, it “would not change travel patterns in the region,” the report said.

It would open with two stations, one in a parking lot at Camden Yards in Baltimore, the other between a McDonald’s and a Hyatt Place hotel on New York Avenue NE in the District, and expand later. Initial ridership would be 1,000 passengers a day in each direction, according to the report.

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“These ridership figures are unlikely to greatly impact economic growth, land use patterns, neighborhood character, or traffic congestion,” according to the assessment.

The Washington metropolitan region had about 4.1 million registered vehicles last year, according to regional planners. About 120,000 vehicles travel the Baltimore-Washington Parkway daily.

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As for Musk’s original “Hyper” version, the “Loop tunnels could potentially serve as Hyperloop corridors," according to the assessment. "However, the potential future use of Hyperloop technology is currently unknown.”

The company says it is more confident about that future, arguing that the system is designed for both, and that the Hyperloop would come into play after technical designs are finished and regulatory approvals are received.

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Construction of the two 35-mile tunnels, including excavating 2,000,000 cubic yards of soil, would take 12 to 20 months, the assessment said. Overall construction, including stations, would total 15 to 23 months, it anticipated. The project must first complete its environmental review and obtain regulatory approvals, a process expected to be completed this year, the report said.

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Skeptics have pointed to Musk’s penchant for overpromising, saying this could be another example. Critics have also mocked the concept as conveniently car-centric for an entrepreneur with an electric car company, saying it does not move the needle on needed mass transit. Kevin DeGood, director of infrastructure policy at the Center for American Progress, dismissed the ambitious tunneling schedule on Twitter with a “Hahahahahahahahahahahahah.”

But the electric-car pioneer and his backers say the privately funded effort would offer widespread benefits.

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“This transportation system would create a significant public benefit due to decreased commute times, decreased urban congestion, decreased public transportation trip times, decreased transportation costs/fares, and decreased greenhouse gas emissions,” the company said.

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Musk has received backing on the overall project from the White House Office of American Innovation, led by President Trump’s senior adviser and son-in-law, Jared Kushner, as well as Maryland Gov. Larry Hogan (R), and it has become part of the Trump administration’s broader push to streamline infrastructure approvals. D.C. Mayor Muriel E. Bowser (D) visited the Boring Company in California last year, walking in a tunnel to learn more about the technology. District officials, who have been generally upbeat but noncommittal about the project, are reviewing the assessment.

“The publication of a draft environmental assessment for this unique project demonstrates the Department’s commitment to preparing for the future of transportation across all modes,” U.S. Transportation Secretary Elaine L. Chao said in a statement, which also said the Boring Company was pursuing the "high-speed tunnel facility to help alleviate area congestion.”

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Chao’s department created a new group called the Non-Traditional and Emerging Transportation Technology (NETT) Council to smooth the way for such projects. The internal group is supposed to “identify jurisdictional and regulatory gaps” that come up as the federal officials consider new transportation technologies.

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“Operational safety issues” with the Loop system “will be addressed in future studies, as will the ultimate engineering and design details,” according to the Transportation Department statement.

In developing Loop projects, the firm currently uses Tesla Model Xs “modified with alignment wheels,” and in some cases “an extended chassis to accommodate up to 16 passengers,” the Boring Company said.

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Musk’s firm is working on similar efforts in Chicago, Las Vegas and Los Angeles.

Musk’s plan to build a tunnel in West Los Angeles was the subject of an environmental lawsuit, which the company agreed to settle last year. Now his company is focusing on another proposed tunnel project near Dodger Stadium.

The environmental assessment looks at how neighborhood aesthetics, wetlands and air quality might be affected, and also describes expected noise and vibration levels, generally presenting a case that such effects would be limited, given that the tunnels will run more than 30 feet underground and will be in “a heavily trafficked corridor.”

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The company said the technology allows for a network of stations on private land, many with a small footprint the size of a few parking spaces. Others would be bigger.

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There might also be spurs off the main D.C.-Baltimore tunnel, reaching communities such as College Park, Greenbelt and Jessup, but the company said there is no final decision on where they might go.

There would be four “launch pits,” where tunnel boring machines would be put into place to begin digging, and up to 70 “ventilation shafts/emergency exits” between 12 and 24 feet across. Some of the ventilation shafts could end up being turned into future stations.

The environmental assessment said that “between one and four” of the launch pit sites could be “repurposed to serve as Maintenance Terminals” and charging stations for the electric vehicles used in the tunnels.

While outside experts have said costs could prove prohibitive for many, the company said they would be comparable to fares for MARC trains, the commuter rail line that the assessment noted “typically takes one hour at a cost of $8."

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