Artist rendering of the interior of planned Purple Line commuter trains in Maryland. (Purple Line Transit Partners)

A federal appeals court ruling on Wednesday will allow Maryland to begin building the Purple Line while a lawsuit opposing it continues, clearing the way for the state to pursue federal funding for a light-rail project that has faced nearly a year of legal delays.

In a major victory for the state, the U.S. Court of Appeals for the D.C. Circuit reinstated the Purple Line’s environmental approval, which a lower-court judge had revoked last year, while the legal case continues.

The ruling allows the state to try to secure $900 million in federal grants for the line’s $2 billion construction while Maryland’s attorney general appeals an earlier ruling in the 2014 lawsuit seeking to block it.

Maryland officials have said construction on the 16-mile line between Montgomery and Prince George’s counties could begin within a few weeks of receiving a federal funding commitment.

“Today’s action by the Court of Appeals is tremendous news for this vitally important project,” said Amelia Chasse, spokeswoman for Maryland Gov. Larry Hogan (R). “Going forward, we will continue to work closely with our federal and local partners to ensure that the Purple Line remains on track and headed toward construction.”

Maryland Attorney General Brian E. Frosh (D) said the court order “will allow construction of the Purple Line to commence, and we will continue to do everything we possibly can to keep the Purple Line moving forward.”

A key issue remains, however: whether the U.S. Department of Transportation will consider the ruling to provide enough legal certainty to sign a multiyear funding agreement with the state for nearly $1 billion in federal aid. The Trump administration has proposed ending federal grants for new transit construction but has said in budget documents that it’s still considering the Purple Line for federal funding.

The Federal Transit Administration referred inquiries Wednesday to the Justice Department. A Justice Department spokesman said lawyers were still reviewing the court order.

Until Wednesday’s ruling, Maryland Transportation Secretary Pete K. Rahn had said the Purple Line was at risk of being canceled because the state was quickly running out of money to continue pre-construction work without the federal reimbursement. Congress has appropriated $325 million to the Purple Line, but the state can’t access that money until a full funding agreement is signed.

“Today’s ruling is good news,” Rahn said. “We will be working with USDOT to move a Full Funding Grant Agreement forward.”

Opponents have argued that allowing construction to begin before the legal case is resolved would cause “devastating” and “irreparable” damage once the state begins cutting trees, wiping out wildlife habitat and harming wetlands.

John M. Fitzgerald, an environmental lawyer and one of the three plaintiffs in the lawsuit, said the ruling shouldn’t allow the state to secure federal aid. He said the law prohibits federal funding for a new transit project unless a region can afford to maintain and operate its existing public transportation system.

“Given the challenges facing Metro, the cuts in Metro and bus service levels, and the fact that Maryland would raid MARC commuter train revenue to pay for the Purple Line debt, that finding is impossible to make,” Fitzgerald said.

The Purple Line is a key part of economic development plans for Washington’s older inner suburbs and is designed to provide faster east-west transit between north-south spokes of the Metro system, as well as Amtrak and MARC commuter rail stations.

The line, with 21 stations, would run trains powered by overhead electrical lines between Bethesda and New Carrollton. Trains would run mostly on local streets and along the wooded Georgetown Branch recreational trail between downtown Bethesda and Silver Spring. Maryland officials have said the line will begin carrying passengers in spring 2022, but that date is expected to be pushed back because of the 11 months of legal delays.

In the ruling, the three-judge panel put on hold the 2016 ruling from a lower-court judge, who had revoked the project’s federal environmental approval until the state recalculated the Purple Line’s ridership projections to reflect Metro’s declining ridership. The state is appealing the ridership ruling, saying a study has shown that the Purple Line would have “robust” ridership, even without the 27 percent of passengers expected to use it to transfer to and from Metro.

The appellate judges wrote that the state “has satisfied the stringent requirements” for putting a lower court’s decision on hold until its appeal is decided. The state had argued that it was likely to win its appeal, it would be “irreparably harmed” if construction was further delayed, and the “balance of the harms and public interest” warranted allowing the Purple Line to proceed.

“This is a joyous day for us,” said Gregory Sanders of the advocacy group Purple Line Now. “We’re closer to breaking ground.”