The Red Line is a rapid transit line operated by the Massachusetts Bay Transportation Authority (MBTA), running roughly northwest to southeast from Alewife station in Cambridge, Massachusetts, through downtown Boston (with transfers to the Green Line at Park Street, the Orange Line at Downtown Crossing, the Silver Line at South Station, Amtrak at South Station as well, and commuter rail at South Station, Quincy Center, Porter and Braintree) then passing through South Boston. South of JFK/UMass it splits into two branches terminating at Braintree or Ashmont stations. At Ashmont passengers may continue via the Ashmont-Mattapan High Speed Line, a light rail line.