Massachusetts Bay Transportation Authority

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.

The MBTA operates an independent law enforcement agency, the Massachusetts Bay Transportation Authority Police. In 2006, 31.60% of workers in the city proper commuted by public transport.

The MBTA is one of only two U.S. transit agencies that operates all of the five major types of transit vehicles: regional (commuter) rail trains, "heavy" rapid transit (subway/elevated) trains, light rail vehicles (trolleys), electric trolleybuses, and motor buses. The other is Philadelphia's Southeastern Pennsylvania Transportation Authority (SEPTA).

The MBTA is the largest consumer of electricity in Massachusetts, and the second-largest land owner, after the Department of Conservation and Recreation. In 2007, its CNG bus fleet was the largest consumer of alternative fuels in the state.