The Metropolitan Atlanta Rapid Transit Authority, more commonly called MARTA, is the largest public rapid-transit system (in both size and ridership) in the Atlanta metropolitan area, and the ninth largest in the United States. MARTA operates a network of bus routes linked to a heavy rail rapid transit system consiting of 48 miles (77 kilometers) of track with 38 train stations. As of 2006, the system has an average weekday ridership of 451,064 passengers. The MARTA acronym is pronounced as a single word, not as individual letters.