The S Castro Shuttle is a Muni Metro line in San Francisco, California. At its inception, it ran from Embarcadero Station downtown to the Castro Street Station during peak periods on weekdays. As of 2016, the line runs from St. Francis Circle to Embarcadero station with limited service to 23rd Street. The line also runs when there is a home game at AT&T Park, continuing from King and 4th Street to West Portal Station for extended hours. During these times the shuttle will occasionally run a three car formation, being the only line that will do this regularly.