On July 30, 2021, about 6:03 p.m. local time, a westbound Massachusetts Bay Transportation Authority (MBTA) light rail vehicle consist (trolley) collided with the rear of another westbound MBTA trolley on the B Branch of the MBTA Green Line near the intersection of Commonwealth Avenue and Harry Agganis Street in Brookline, Massachusetts (see figure). Each trolley consisted of two coupled railcars. Both of the struck trolley’s railcars derailed, and the lead railcar of the striking trolley derailed. As a result of the accident, 24 passengers and 3 crewmembers were transported to local hospitals with minor injuries. Visibility conditions at the time of the accident were daylight with clear skies, no precipitation, and a temperature of 79°F. MBTA estimated equipment damage to be about $2 million.
We determined that the probable cause of the July 30, 2021, Massachusetts Bay Transportation Authority trolley collision and derailment was the operator’s acceleration to 33 mph as he departed the St. Paul Street Station, exceeding maximum authorized speed due to his loss of situational awareness and colliding with the moving trolley.