Jelaskan Freight service dari MBTA Commuter Rail

Freight service is operated over most of the MBTA Commuter Rail system by several private railroads. CSX Transportation operates freight on most southside lines, of which the outer portion of the Worcester Line has the most freight traffic. Massachusetts Coastal Railroad operates south of Middleborough on the Middleborough/Lakeville Line, as well as on future South Coast Rail trackage. The Fore River Railroad operates between Braintree Yard and East Braintree on the Old Colony mainline and the Greenbush Line. The Providence and Worcester Railroad shares tracks with Providence/Stoughton Line trains between Providence and Wickford Junction; it uses a freight-only track between Providence and Central Falls. No freight operates on the Needham Line, the Northeast Corridor between Readville and Back Bay, the Old Colony mainline between Boston and the Greenbush Line junction in Braintree, the Plymouth/Kingston Line, and most of the Greenbush Line.

CSX also operates on most northside lines; prior to its 2022 purchase by CSX, Pan Am Railways operated over these lines. Pan Am Southern (planned to be replaced by the Berkshire and Eastern Railroad) operates over the Fitchburg Line west of Ayer. Their combined Freight Main Line between Mechanicville, New York, and Mattawamkeag, Maine, shares tracks with sections of the Fitchburg, Lowell, and Haverhill lines. No freight service is operated over the Newburyport/Rockport Line north of Salem.

Weight limits and loading gauge vary across the system. The full Framingham/Worcester line is rated for car weights of , sections of lines that are part of the Freight Main Line for , and other lines for lower weights. The western portion of the Framingham/Worcester Line and the southern section of the Providence/Stoughton line can accommodate cars up to  (AAR Plate H or Plate K). The Fitchburg Line west of Ayer can accommodate cars up to  (AAR Plate J), while most of the other northside lines can accommodate up to  (AAR Plate F). The inner Fitchburg and Newburyport/Rockport Lines, and the southside except for the outer Framingham/Worcester Line, have height restrictions smaller than Plate F.