The woman allegedly "took a wrong turn" in her gray Toyota Camry around 10 a.m., stopping all underground Muni service to and from the West Portal and Van Ness Avenue stations, Muni spokesman Judson True said.
Aboveground motor coach shuttles were provided until service to the underground trains was restored just before 10:40 a.m.
True said no injuries were reported and the tracks were not damaged.
The woman, who was not cited, was escorted home, according to the San Francisco Police Department.
