The
Ashmont–Mattapan High Speed Line, also known as the "M-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 and exclusively uses historic
PCC streetcars for rolling stock. Passengers must transfer at
Ashmont to access the rest of the Red Line, which uses heavy rail metro rolling stock.