The Mattapan Line 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.