Bay Area Rapid Transit (BART) is a rapid transit system serving the San Francisco Bay Area in California. BART serves 50 stations along six routes on 131 miles (211 kilometers) of rapid transit lines, including a 10-mile (16 km) spur line in eastern Contra Costa County which uses diesel multiple-unit trains and a 3.2-mile (5.1 km) automated guideway transit line to the Oakland International Airport. With an average of 411,000 weekday passengers and 118 million annual passengers in fiscal year 2019, BART is the fifth-busiest heavy rail rapid transit system in the United States and is operated by the Bay Area Rapid Transit District which formed in 1957. The initial system opened in stages from 1972 to 1974. The system was extended most recently on June 13, 2020, when Milpitas and Berryessa/North San José stations opened as part of the Silicon Valley BART extension in partnership with the Santa Clara Valley Transportation Authority (VTA).