line's color. The MBTA launched the Mattapan Line Transformation project in 2019, though it was largely inactive until 2022. The project aims to replace the PCC trolleys with light rail vehicles as the Green Line fleet turns over, restore the line's ability to operate during snowstorms, rebuild all eight stations, replace track and signals, and repair bridges. Rehabilitation of the existing fleet is happening at the same time, to extend trolley life a few more years until LRVs arrive. Route The line begins and ends within the city of Boston, but most of the southern half of its route is in the northern part of the neighboring town of Milton. It follows the right-of-way of two former Old Colony Railroad branches which had commuter rail service until the 1920s. Much of the route parallels the Neponset River, crossing it twice. The right-of-way is owned by the MBTA and has only two at-grade crossings on its route. Between Cedar Grove and Butler stations, the line runs through the center of the Cedar Grove Cemetery. Station listing Accidents On March 20, 1979, three trolleys collided between Central Avenue and Valley Road stations. The first two trolleys had stopped to avoid a police car, which had become stuck on the tracks while the officer was investigating teenagers drinking near the line. A third trolley was unable to stop in time while approaching around a blind curve; it slammed into the first two trolleys, causing injuries, but no deaths. Using funding from the American Recovery and Reinvestment Act of 2009, the MBTA conducted a pilot test of technology similar to a collision avoidance system in an automobile, using radar and increasingly fast beeping to warn train operators of obstacles ahead. Like positive train control, it would stop the train if the driver did not take action to avoid an impending collision. If successful, the system would be considered for deployment on the Green Line, where multiple collisions had occurred in recent years. On November 26, 2014, an out-of-service streetcar collided with an in-service streetcar near Cedar Grove. Seven people were injured. On December 29, 2017, a collision between two in-service streetcars caused 17 injuries. The accident, caused by operator error, reduced the line to five operable streetcars. Rolling stock The rolling stock consists of rebuilt PCC streetcars, which were formerly part of a fleet shared with the Green Line. The historic rolling stock is