AC Transit is the main bus transit operator in the East Bay region of the San Francisco Bay Area, California. AC Transit is the third largest bus operator in California, serving the western portions of Alameda and Contra Costa counties, with a fleet of over 600 buses operating 130 routes. The agency was founded in 1960 as the successor of the bankrupt Key System.
AC Transit's primary services are its local bus routes, which serve the entire East Bay region from Richmond to Milpitas; "Transbay" regional routes, most of which operate between the East Bay and San Francisco via the Bay Bridge; and the Tempo bus rapid transit line from Oakland to San Leandro.