Jabarkan Service dari MBTA Commuter Rail

The system consists of twelve lines – four of which have branches – radiating from downtown Boston. Eight "southside" lines terminate at South Station, with four (Framingham/Worcester, Needham, Franklin/Foxboro, and Providence/Stoughton) also running through Back Bay station. Four "northside" lines terminate at North Station. The Kingston Line and Middleborough/Lakeville Line are often grouped together as the Old Colony Lines. The lines vary in length from the  Fairmount Line to the  Providence/Stoughton Line, with typical lengths in the  range. The system has  of revenue trackage and covers roughly the eastern third of Massachusetts plus central Rhode Island.

Most lines do not share trackage outside the Boston terminal areas, with several exceptions. The Providence/Stoughton Line and Franklin/Foxboro Line both use the Northeast Corridor between  and South Station, with the Needham Line also sharing the tracks between  and South Station. The Old Colony Lines and the Greenbush Line all use the Old Colony mainline between South Station and . The Haverhill Line and Newburyport/Rockport Line share tracks between North Station and near . A small number of Haverhill Line trains use the inner Lowell Line and the Wildcat Branch, while a small number of Franklin/Foxboro Line trains use the Fairmount Line rather than the Northeast Corridor. Several Amtrak intercity routes run on MBTA tracks: the  and  over the Providence/Stoughton Line, the  over the Framingham/Worcester Line, and the  over portions of the Lowell and Haverhill lines. Private companies also operate freight service over much of the system (see ).