77A (MBTA bus)

Boston-area trolleybus system

A trolleybus on the #71 route leaves the Harvard Bus Tunnel
Operation
Locale	Boston, Belmont, Cambridge, and Watertown, (formerly also Arlington, Brookline, Chelsea, Everett, Malden, Medford, Newton, Revere, and Somerville), Greater Boston, Massachusetts, United States
Open	April 11, 1936 (1936-04-11)
Operator(s)	1936–47: Boston Elevated Railway Co.; 1947–64: Metropolitan Transit Authority; 1964–present: Massachusetts Bay Transportation Authority (MBTA)
Infrastructure
Electrification	600 V DC

The Boston-area trolleybus (or, as known locally, trackless trolley) system forms part of the public transportation network serving Greater Boston in the U.S. state of Massachusetts. It opened on April 11, 1936, and since 1964 has been operated by the Massachusetts Bay Transportation Authority (MBTA). It currently includes two physically isolated networks: one serving the towns of Cambridge, Belmont, and Watertown, the other – the Silver Line (Waterfront) – located in the city of Boston proper. Prior to 1964, several additional trolleybus lines were in operation in Boston proper. Measured by fleet size, the system was the third-largest trolleybus system in the United States at its peak (end of 1952), with only the Chicago and Atlanta systems having more trolleybuses than Boston's 463.

In the present system, four routes fan out from the Harvard Bus Tunnel at Harvard Square station, running through Cambridge, Belmont, and Watertown. Those lines are the remains of a once-extensive system of trackless trolleys in the area, which was largely formed from former streetcar lines. Additionally, the 2004-opened Silver Line (Waterfront) is a bus rapid transit service using dual-mode buses which run as trolleybuses in the Waterfront Tunnel.

The first trackless trolley line in the Boston transit system was opened by the Boston Elevated Railway (BERy) on April 11, 1936. Replacing a streetcar line over the same route, it was an unnumbered crosstown line running from Harvard station east to Lechmere station. Additional lines were opened in 1937, and by 1942, the system had 14 lines, of which 10 were former streetcar lines and four were former motor bus lines. In 1947, the BERy was succeeded by the public Metropolitan Transit Authority (MTA) as the operator of Boston's urban transit system, and in 1964, the MTA was replaced by the Massachusetts Bay Transportation Authority (MBTA), which remains the system's operator today.