Norfolk Southern and Pan Am Railways. They currently have a partnership called Pan Am Southern. PAR runs the trains while NS performs the track improvements and maintenance. This allows for NS to run-through auto-carriers and containers to Ayer MA, the current end of the PAS agreement, and gives them full access to the north-south River Line to New Haven and New Hampshire.
Since NS has just purchased the old D&H whose eastern terminus is at Mechanicsville, NY where the old B&M's (PAR/PAS mainline) terminates, this would give them a complete system east. This used to be their big interchange point, and today is an intermodal terminal for traffic both east to Boston via the Hoosic Tunnel and north-south to Rouse's Point for interchange with CN, and south to the NYC region. With ongoing plans to widen (raise) the tunnel, this would mean complete double stacks on the B&M line instead of cut stacks which are lowered at the intermodal terminal in Mech'ville.
This might not sound like much since PAR is probably a Class 3 railroad today - it's hard to believe that their management took two Class 1s and destroyed them to this point, however, this would complete NS's Crescent Corridor from the Canadian Maritimes right down to their southern region, and it would mean ROW improvements and other badly needed upgrades as PAR, former Guilford Transportation Industries, had neglected the maintenance on the system. Even with the PAS partnership, NS put in over $40 million in track work to bring the speeds up from 15 mph with other slower places to at least 40 mph in some places, but that still is not enough and there are still stretches of track that need improvement on the West End.
John