The Metropolitan Atlanta Rapi Transit Authority or MARTA (pronounced /ˈmɑrtə/) is the principal rapid-transit system in the Atlanta metropolitan area and the ninth-largest in the United States. Formed in 1971, MARTA operates a network of bus routes linked to a heavy rail rapid transit system consisting of 48 miles (77 km) of track with 38 train stations. MARTA operates primarily in Fulton and DeKalb counties, with very limited bus service to Cobb County, 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 2006, the system has an average of 451,064 passengers per day.