A state appeals court says a woman who was robbed at a BART station in Oakland can’t hold the transit agency legally responsible because she was on the platform, not the train.

Kathryn Cissney said she was waiting for a train at the Coliseum Station on an evening in April 2017 when a large group of youths came through the parking lot, jumped over the fare gates and reached the platform, where they beat her and stole her cell phone. She said they then boarded a train and robbed some of its passengers, one of whom has also sued BART.

Cissney’s suit in Alameda County Superior Court said BART was well aware of such “mob-style attacks” at the station, where there had been three similar incidents a month earlier. Cissney alleged that BART did little or nothing to prevent the attacks or apprehend the attackers and was more interested in trying to “protect its public image.”

The suit argued that BART, as a “common carrier” offering transportation services, had a legal duty to protect its passengers from harm that it might have prevented. Judge Robert McGuiness disagreed and dismissed the suit last February, and the First District Court of Appeal in San Francisco upheld his decision Wednesday.

Because Cissney had not yet boarded a train, “the relationship of carrier and passenger had not yet been established,” Justice Alison Tucher said in the 3-0 ruling.

Tucher cited a state Supreme Court ruling from 1893 observing that a passenger “is exposed to countless hazards” while traveling, and is “wholly in (the) charge of the carrier,” but faces no similar dangers while waiting in the station.

She said the rule has some exceptions: A transit agency may have a special duty to protect a passenger who is being escorted to the boarding area by an employee or to protect passengers from mobile hazards, like cable cars passing through a boarding area or jet blasts from an airplane. But she rejected the lawsuit’s contention that BART was obliged to protect a passenger who was on an elevated platform and had no way to flee because the youths were blocking the entrances, stairways and escalators.

Under California case law, Tucher said, “standing on a BART platform waiting for a train to arrive does not establish that the carrier, before it has taken affirmative steps to accept a passenger onto a train, has a heightened duty to protect that prospective passenger from risks that are not incident to the journey itself.”

Cissney could ask the state Supreme Court to review the case. Her lawyer could not be reached for comment Friday. BART declined to comment on the ruling.

Bob Egelko is a San Francisco Chronicle staff writer. Email: begelko@sfchronicle.com Twitter: @BobEgelko