Train service was restored hours after protesters demonstrating against the Ferguson, Mo. grand jury decision shut down Bay Area Rapid Transit system Friday by chaining themselves to trains in Oakland.
The action led to major delays, she said.
A protest in St. Louis clogged a mall during the Black Friday morning shopping rush, and earlier this week another group clogged the 101 Freeway near downtown L.A. during peak pre-Thanksgiving travel time.
Police arrested the demonstrators for various offenses, but mainly for obstruction of train movements, she said.
Earlier this week, a grand jury voted not to indict white police Officer Darren Wilson in the shooting death of Michael Brown, an unarmed young black man, in August. The decision has led to protests in numerous cities across the country. Oakland has been the scene of some of the most violent and intense demonstrations.