A woman who was hit by a San Francisco Municipal Railway bus on Saturday near Lake Merced has died, the San Francisco medical examiner's office confirmed Monday morning.

The woman, identified by the medical examiner's office as 72-year-old Daly City resident Eileen Barrett, was struck by an outbound 18-46th Avenue bus at about 4:30 p.m. at Lake Merced Blvd and John Muir Dr, Muni spokesman Paul Rose said.

She was transported to a hospital with serious injuries, but it was initially thought she would survive, Rose said.

The bus operator was expected to undergo drug and alcohol testing, as is standard protocol for such accidents, Rose said.

"While this incident is still under investigation, we offer our condolences to the family and friends of Ms. Barrett," Rose said. "Our top priority is the safety of those who utilize San Francisco streets, and we will work with authorities to find the cause of this accident in order to prevent it from happening again."