Planners who oversee development on federal property in the Washington region are questioning the viability and benefits of a proposed high-speed train line between Washington and Baltimore, citing negative effects to land and sowing doubt about the project’s future.

Members of the National Capital Planning Commission (NCPC) say it is not clear whether the benefits of the maglev train would outweigh the project’s “enormous environmental and planning costs.” The commission, which represents the interest of federal agencies, reviewed the proposal Thursday ahead of making recommendations to the Federal Railroad Administration (FRA), which is leading the project’s environmental review.

“In the big picture, the concern is that we’re not sure how this can actually happen given the constraints of several agencies involved,” said Commissioner Peter May, who represents the National Park Service.

The train’s path would cut through multiple federal parcels with two proposed alignments — east and west of the Baltimore-Washington Parkway.

The commission’s objections echo concerns from environmental groups and some elected leaders about the disruptions a maglev system could bring to federal research facilities, the region’s wildlife and parkland. Thursday’s discussion offered rare insight about how federal agencies along the path view the proposal. Those agencies have declined to comment publicly on the plans.

The proposal for a superconducting magnetic levitation train system is in its last phase of a federal environmental review. The FRA is on pace to select a preferred route and issue a final recommendation, expected in early 2022. If the project receives FRA clearance, additional federal, state and local permitting would be required before construction.

Project proponents note the train service would move passengers between the nation’s capital and Baltimore in 15 minutes, serving as the first segment of a system that eventually could carry passengers between Washington and New York in an hour.

The D.C.-to-Baltimore stretch would cost between $13.8 billion and $16.8 billion to build, depending on the alignment chosen, according to the FRA. Baltimore Washington Rapid Rail, which is developing the system with sister company Northeast Maglev, has said it secured $5 billion from Japan.

Lauren Nelson, a spokeswoman for BWRR, said in an emailed statement Friday that she welcomed the commission’s comments and that the group hopes to continue to have “productive conversations” with the commission as the project study moves forward. The rail group, she said, is committed to “comply with all federal, state, and local mitigation requirements.”

The planning commission, which has authority over development on federal land, could be critical to the eventual construction of the high-speed line.

If the maglev receives FRA clearance to proceed, BWRR would need to negotiate land acquisition agreements with the federal government for land owned by the National Park Service, the Agriculture Department, NASA and the Fish and Wildlife Service, among other agencies.

Proponents also would probably need to negotiate the use of parcels of federal property during construction. Each federal agency affected by the project would need to submit the proposed changes to the NCPC for review, according to the commission.

The proposed 40-mile high-speed line would travel aboveground for up to nine miles, mostly in Prince George’s County, crossing or touching upon the parkway, the nation’s largest agricultural scientific installation and the only national wildlife refuge established to support research.

May said it would affect up to 50 percent of the parkway’s scenic views. Under one of the two proposed alignments, the train would cross over the parkway to get to a 180-acre paved maintenance yard at the Beltsville Agricultural Research Center.

“The things that make it a parkway and not just a highway will be diminished by this construction,” said May, an associate director for the capital region at the Park Service. “What’s being proposed is a set of impacts that are so substantial, and I mean more substantial than anything that I have seen in my Park Service career.”

Proponents of the maglev project say the two alignments under consideration were selected out of more than a dozen possible options because they would have the least effect on homes and other private property, while also keeping the project economically feasible.

Some other routes included residential displacements and a suboptimal geometry, such as too many curves, Nelson said.

“We made it our mission not to take a single home for this project,” she said.

Building close to the parkway would minimize bisecting large areas that are home to sensitive species and habitats, according to BWRR.

“Our goal is not to disturb the Parkway, but rather to take more than 11.38 million cars off roads per year so that instead of endless traffic, the parkway, designed for 50,000 cars per day but now serving 120,000, can actually be used for scenic driving again,” Nelson said in the email.

Planner Michael Weil said Thursday the commission will seek to slow the process so the public has more time to get information about effects and mitigation before the FRA makes a possible route recommendation.

The commission also is recommending the FRA revive one or more alignments that do not encroach on federal parkland. The current two options would cut through woods and permanently alter parks, recreational facilities and wetlands. As many as 1,000 acres, including up to 328 acres of federal land, would be affected, according to the federal environmental review.

“Of particular concern are physical impacts to recreational facilities and parklands, cultural resources, viewsheds, water resources, wetlands/waterways, ecological resources (forests) and soils/farmlands,” according to a commission report. “While it may be possible to lessen these impacts to an extent, their magnitude would likely make it impossible to fully mitigate in a meaningful manner.”

Besides concerns about environmental effects, planners and May said the physical encroachment of the maglev on the parkway could be detrimental to scenic views and the historic character of the route. The only way to protect it, they said, is by keeping the maglev off federal parkland, either by moving the train line underground or using a different alignment.

The project, the report concluded, “would provide for-profit transportation for a relatively small market with a heavy reliance on the use of federal property.”

Arrington Dixon, a commissioner appointed by D.C. Mayor Muriel E. Bowser (D), said he rode a maglev train in Asia and was excited about the idea of bringing the technology to the Washington region. But he noted concerns about the project and said investing in existing rail infrastructure could be the best option.

“Is the juice going to be worth the squeeze? Is the result going to be worth the damage?” Dixon said. “I’m excited about it, but a lot of things excite us. Do we really want to go through the intrusion to our land and to our area?”