A citizens’ group opposed to the Southwest Corridor light-rail line has appealed a judge’s decision to throw out a lawsuit challenging the $1.9 billion project.

The Lakes and Parks Alliance first sued the Metropolitan Council in U.S. District Court more than three years ago, claiming the regional planning body violated federal law when it chose its current route before completing necessary environmental studies.

But last month, Judge John Tunheim ruled in favor of the council, writing that it “did not irreversibly … commit itself to a specific light-rail route, despite the appearance that it did.”

In announcing its appeal to the Eighth Circuit Court of Appeals Thursday, the alliance argued that the council limited itself to the current route by entering into agreements with the Minneapolis Park and Recreation Board, as well as with the cities of Minneapolis and St. Louis Park. The Minneapolis agreement was reached with the Met Council during the summer of 2014, and was mediated by chief magistrate Judge Arthur Boylan.

However, Tunheim wrote in his decision that the pacts were “promises that could be broken.”

The primary area of contention for the alliance is the Kenilworth corridor, a stretch of land in Minneapolis straddling Cedar Lake and Lake of the Isles that is popular with bicyclists and pedestrians. The 14.5-mile line is slated to run from downtown Minneapolis to Eden Prairie, with passenger service beginning in 2023.

“The case will be argued by attorneys,” said alliance spokeswoman Mary Pattock. “But as a citizen, I believe it destroys people’s trust in government to find out that a negotiated, written agreement with a public agency, intended from the outset to be binding, can turn out to be just ‘a promise that can be broken.’ ”

The alliance said issues covered in the Minneapolis “memorandum of understanding” that “become nonbinding” with Tunheim’s decision include the design of a shallow tunnel for light-rail trains through the Kenilworth corridor, the proposed 21st Street Station, pedestrian access to the train, noise mitigation and landscape restoration.

The pact with the Minneapolis park board included Met Council assurances to mitigate damage to “environmentally and historically sensitive areas” in the Grand Rounds Scenic Byway System, a series of bike and pedestrian paths.

But Met Council Chairwoman Alene Tchourumoff said Thursday that the alliance “spent almost four years challenging the ... project in court and had every opportunity to air neighbors’ concerns. At the end of the day, the court confirmed that the council complied with the law throughout the 11-year environmental review process.”

Tchourumoff said she’s confident that the Appeals Court will affirm Tunheim’s decision, and noted that the rail project is on track, with construction to begin this fall.