The Ashmont–Mattapan High-Speed Line, commonly referred to as the Mattapan Trolley, is a partially grade-separated light rail line which forms part of the MBTA's Red Line rapid transit line. The line, which runs through Boston and Milton, Massachusetts, opened on August 26, 1929, as a conversion of a former commuter rail line. It exclusively uses PCC streetcars built in the 1940s. Passengers must transfer at Ashmont to access the rest of the Red Line, which uses heavy rail metro rolling stock.

Ashmont station is a Massachusetts Bay Transportation Authority (MBTA) intermodal transit station located at Peabody Square in the Dorchester neighborhood of Boston, Massachusetts. It is the southern terminus of the Ashmont branch of the rapid transit Red Line, the northern terminus of the connecting light rail Ashmont–Mattapan High-Speed Line, and a major terminal for MBTA bus service. Ashmont has two side platforms serving the below-grade Red Line and a single side platform on an elevated balloon loop for the Mattapan Line. The station is fully accessible for all modes.