The San Francisco Bay Area Rapid Transit System, commonly known as BART, is a rapid transit system serving the San Francisco Bay Area. It connects the cities of San Francisco, Oakland, Berkeley, Fremont, and other surrounding areas. BART operates five lines on 104 miles of track, with 44 stations in four counties. It is the fifth-busiest rapid transit system in the United States, carrying an average of 423, 000 passengers per weekday.