The Massachusetts Bay Transportation Authority, often referred to as the MBTA or "The T", is the public operator of most bus, subway, commuter rail, and ferry routes in the greater Boston, Massachusetts area. Officially a "body politic and corporate, and a political subdivision" of the Commonwealth of Massachusetts, it was formed in 1964. Its immediate predecessor, the Metropolitan Transit Authority (MTA), was immortalized by The Kingston Trio in the popular folk-protest lament "M.T.A." Locals call it "The T", after its logo, the letter T in a circle, adopted in the 1960s and inspired by the Stockholm metro. In 2008, the system averaged 1.3 million passenger trips each weekday, of which the subway averaged 598,200, making it the fourth busiest subway system in the United States. The Green Line and Ashmont–Mattapan High Speed Line comprise the busiest light-rail system in the U.S., with a weekday ridership of 255,100.