Members of a citizens group challenging the Southwest light rail project attended what may be their final day in court Thursday as attorneys argued their case against the Metropolitan Council before the Eighth U.S. Circuit Court of Appeals.

The Lakes and Parks Alliance of Minneapolis argues the Met Council improperly committed to a path for the line — specifically through the Chain of Lakes in Minneapolis — before environmental reviews were complete. A district judge ruled against the group one year ago, saying that agreements with cities along the route amounted to "promises that can be broken."

Meanwhile, the Southwest light rail project has already broken ground. The nearly 15-mile line will extend from downtown Minneapolis to Eden Prairie. At an estimated cost of about $2 billion, it would be the state's largest public works project.

Two federal appeals court judges, Bobby Shepherd and Jonathan Kobes, peppered attorneys with questions at the federal courthouse in St. Paul Thursday morning. Most discussion centered on whether the alliance had pursued the appropriate legal strategy to make their argument.

Shepherd noted that the Federal Transit Administration has already certified that the environmental review met the legal requirements.

"What can the court really do at this point? Hasn't the ship sailed, so to speak?" Shepherd asked. He later asked whether the FTA should have been a party to the case.

The main point in contention is a narrow portion of the route between Lake of the Isles and Cedar Lake, known as the Kenilworth corridor, now shared by freight trains and popular recreational paths. Under the current plan, the light rail would travel alongside freight but dip into a tunnel for a portion of the corridor. Other options included routing freight through St. Louis Park, which would have created less congestion at the bottleneck.

The alliance argues that the Met Council improperly limited other alternative routes when it signed agreements in 2014 with St. Louis Park and Minneapolis. The Minneapolis agreement said, among other things, that freight and light rail trains would operate together in the corridor. The final environmental review was completed in May 2016.

The alliance's filing points out that then-Minneapolis Mayor Betsy Hodges objected to the Met Council's legal argument that its agreements could effectively be ignored. "The city of Minneapolis in no uncertain terms considers them to be binding," Hodges wrote in an e-mail to the Met Council.

"We do believe that was a binding commitment," said Richard Landon, an attorney for the alliance.

Charlie Nauen, an attorney representing the Met Council, said memorandums of understanding are by their nature nonbinding agreements.

"This political process did not result in a binding commitment," Nauen said.

The justices reached no decision in the case on Thursday.

Eric Roper • 612-673-1732 Twitter: @StribRoper