Metro has won an appeal of a slip-and-fall lawsuit, reinforcing its claim that it is immune as a government agency from such suits.

The Maryland Court of Special Appeals overturned a lower court's award of about $64,000 to a woman who broke her ankle after exiting a Metro train.

The decision may further endanger the chances of existing cases against the transit agency -- especially for riders in Maryland.

The case dates to 2007, when Veronica Tinsley slipped on a wet platform at the Cheverly station on the Orange Line. She argued that the platform had been mopped during rush hour, contrary to an agency rule, and no signs warning riders were placed there. A jury sided with her and awarded her damages.

But Metro appealed the decision and won. The court opinion says that Virginia, Maryland and the District of Columbia passed along their "sovereign immunity" to Metro when they formed the agency.

"The decision is consistent with a long line of cases," Metro spokesman Dan Stessel said in an email. "In our view the lower court erred, we appealed and the appellate court rendered the correct decision."

For Metro, it's a victory that may help dissuade other riders from filing suits -- and doom some existing cases.

The agency is a frequent target of lawsuits. At least eight suits seeking damages for injuries have been filed against the agency in federal courts since September.

And others have lost on those terms before. Following rounds of court battles, a family lost its suit against Metro after their son, Richard Smith, had a fatal heart attack in 1998 while climbing up a downed escalator on a hot July day at the Bethesda station.

But a lead attorney in the pending high-dollar suit against Metro stemming from the deadly 2009 Fort Totten crash says the agency isn't entirely immune in that case. Nine people were killed when one train rear-ended another on the Red Line. The families of the victims are suing Metro and some of the manufacturers of the safety equipment that failed that day.

"We recognize and concede that they have immunity for some issues," Patrick Regan said. "They will never have immunity in all claims."

He added that the facts in the crash are completely different than in the Tinsley case, and that Maryland case law wouldn't affect his case pending in D.C.'s federal court.

"At the end of the day, they will be held responsible," he said.