Bay Area Rapid Transit (BART), is a rapid transit system serving the San Francisco Bay Area. The heavy-rail public transit and subway system connects San Francisco with cities in the East Bay and suburbs in northern San Mateo County. BART operates five routes on 104 miles (167 km) of line, with 44 stations in four counties. With an average of 373,945 weekday passengers, 176,616 Saturday passengers, and 119,247 Sunday passengers in January 2013, BART is the fifth-busiest heavy rail rapid transit system in the United States.

BART is operated by the San Francisco Bay Area Rapid Transit District, a special-purpose transit district that was formed in 1957 to cover San Francisco, Alameda County, and Contra Costa County. The acronym is widely pronounced "bart", not spelled out.

BART is a rapid transit and commuter rail system and an alternative to highway transportation, especially to avoid congestion on the San Francisco Bay Bridge, which connects San Francisco to the East Bay suburbs and the city of Oakland. As of 2013 ^[update], the BART system is being expanded to San Jose with the Silicon Valley BART extension. (more...)