Federal transit officials say more environmental study is needed along part of the proposed Southwest light-rail route where a crash-protection wall will be installed to separate freight and LRT trains.

It’s unclear whether the study will add more time and expense to the embattled $1.9 billion project — the biggest public works project in state history.

The $20 million wall was added to the Southwest project this fall at the behest of BNSF Railway, which owns a 1.4-mile stretch west of Target Field in Minneapolis where freight and light-rail trains will run side by side. BNSF has said it requested the concrete barrier, which will reach 10 feet high in some spots, for safety reasons.

The Federal Transit Administration (FTA) informed the Metropolitan Council of the need for a “supplemental environmental assessment” on Monday afternoon.

“At this point, we don’t know what, if any, impact this will have on the construction timeline,” said Mark Fuhrmann, deputy general manager of Metro Transit, in a statement. “We will be discussing this further with FTA and our project partners.” The council said the study will be done with existing project staff and consultants.

The 14.5-mile LRT line will connect downtown Minneapolis to Eden Prairie, with passenger service expected to begin in 2022. The wall will be erected between the Royalston Avenue/Farmers Market and Bryn Mawr stations.

News regarding the additional study comes at a challenging time for the project.

The Met Council rejected bids to build the line in August as too expensive and “unresponsive,” a move that added four months and $12 million to $16 million to the project budget.

The regional planning body retooled the project. New bids are due Jan. 9, with the selection expected in the spring.

Meantime, U.S. District Judge John Tunheim is expected to rule soon on whether a lawsuit, filed by neighbors who claim the project violated federal environmental laws, can proceed.

Mary Pattock, a spokeswoman for the Lakes and Parks Alliance, which filed the suit, said Tuesday that “the FTA is addressing the very point of our lawsuit — that the Met Council is recklessly disregarding environmental laws.

“The Met Council’s disregard of the law is a long-standing pattern,” Pattock said. “They are trying to keep this project moving, spending millions of public dollars and risking private money, all the while ignoring the lawsuit, the Legislature, the city, the community. This is recklessness to the point of craziness.”

The FTA is expected to pay for half of the project’s cost, about $929 million. To date, the Met Council reckons about $220 million in local funds has been spent for Southwest’s planning and engineering work.

The FTA issued a statement saying the decision was made after it conferred with the Met Council, with both bodies agreeing that a supplemental environmental assessment is “needed to evaluate the potential environmental impacts of a wall.”

In recent weeks, Rep. Frank Hornstein, DFL-Minneapolis, has been leading a petition drive that would trigger a state-led study assessing the effects the wall would have on the environment. While much of the area along the wall’s path is part of a city-owned lot used for storing gravel and other items, the stretch also hems the Bryn Mawr Meadows Park and the Cedar Lake bike and pedestrian trail.

Hornstein said the wall would affect noise, surface and groundwater, animal habitat, and access to bike paths. “There are a lot of unanswered questions about the wall,” he said.

The Met Council said the study “will include some level of public involvement,” likely in 2018.

Earlier this month, the FTA said the BNSF wall will “adversely affect” the historic rail district in Minneapolis, and required a “mitigation plan.” At the time, the Met Council said the plan would not delay the project schedule. It would tap its contingency fund to pay for the plan.