There are currently four trolleybus routes in the Boston, Massachusetts area, all run by the Massachusetts Bay Transportation Authority (MBTA) in the Harvard Square area, and all former streetcar lines (the last four not connected to the Tremont Street Subway to survive). The MBTA and its predecessors once ran a large system of trackless trolleys, but most have been replaced by buses; the four survived, in part, because of the necessity for left-hand doors in the Harvard Bus Tunnel. They are all stored overnight in the North Cambridge Carhouse, the northern terminus of the 77A. Trackless trolleys do not run on Saturday evenings and Sundays; instead conventional buses cover the routes.
In 2004, the MBTA began receiving a fleet of new trackless trolleys from Neoplan, to replace older Flyer trolleybuses dating to the 1970s. The newer vehicles meet Americans with Disabilities Act standards (see MBTA accessibility).
Additionally, the Silver Line Phase II uses dual-mode buses and until early 2006 also used some of the new Neoplan trackless trolleys pending the entry of the entire dual-mode fleet into service. As of July 2006, the Neoplan trackless trolleys have now all been transferred to the following routes, and most of the Flyer trolleybuses have been retired, with up to 10 (some sources say 12) being kept as spares.
The 71 Watertown Square - Harvard Station via Mt. Auburn St. begins at the Harvard Bus Tunnel lower level and leaves via the south exit onto Mount Auburn Street. It heads west into Watertown, ending at Watertown Square.
At the Harvard end, to turn around, the trolleybus exits the tunnel and makes a hard left onto Massachusetts Avenue and a right on Garden Street, and then turns right on Waterhouse Street and right on Massachusetts Avenue to return to the tunnel. The Watertown end has a loop on private right-of-way for turning around and picking up/dropping off passengers.
To turn around, the 72 leaves the south portal of the tunnel and turns left on Mount Auburn Street. It turns right on Eliot Street, right on Bennett Street and right on private right-of-way to go straight across Mount Auburn Street into the tunnel. At the west end, the 72 simply makes a U-turn across the wide median of Aderdeen Avenue. On Saturday evenings and Sundays, the 72 is combined with the 75 bus and the route extends to Belmont center.
September 4, 1958 was the last day of streetcar service on the 73 (and 71 and 77A), after which trackless trolleys have run. As a streetcar line, the turnback loop was further west along Trapelo Road at Cushing Square. Streetcars first ran to Waverley Square on October 1, 1898. The old streetcar tracks can be seen at Waverley Square.