The Metropolitan Atlanta Rapid Transit Authority or MARTA is the principal rapid transit system in the Atlanta metropolitan area and the eight-largest in the United States. Formed in 1971 as strictly a bus system, MARTA operates a network of bus routes linked to a rapid transit system consisting of 48 miles (77 km) of rail track with 38 train stations. MARTA operates almost exclusively in Fulton and DeKalb counties, with bus service to two destinations in Cobb county (Six Flags Over Georgia and the Cumberland Transfer Center next to the Cumberland Mall) and a single rail station in Clayton County at Hartsfield Jackson Atlanta International Airport. MARTA also operates a separate paratransit service for disabled customers. As of 2012, the average total daily ridership for the system (bus and rail) was 422,400 passengers.