The Fairmount Line or Dorchester Branch is a line of the MBTA Commuter Rail system in Boston, Massachusetts, USA. Except for a short portion in Milton, it lies entirely within Boston, progressing in a southwesterly trajectory, passing through the neighborhoods of Dorchester, Mattapan and Hyde Park. It sees service roughly every half hour during rush hours and approximately every hour or less at other times, though with no night service. Weekend service began on November 29, 2014.