The Newport Southern Joint Line is the northern half of the old joint line from the Canadian border down the Connecticut River. This joint line suffered from having part of it under the control of the Boston & Maine (a railroad that, at least since the second world war, has suffered from what appears to have been a death wish) and slowly ran down until it was barely functional, at which point Vermont stepped in and took possession of the parts that the B&M used to own. The line south of Wells River ended up in the hands of the state of Vermont (being operated as the Connecticut Valley division of the Washington County Railroad), and the line north ended up in the hands of the PV&T via the purchase of the Canadian Atlantic Railway.
The PV&T wasn’t terribly happy with the condition of or the amount of traffic on this part of the CAR, but when they started making noises about abandoning it the state stepped in and asked to buy it and then having the Vermont Rail System operate the thing.
The Parsons Vale wasn’t terrifically happy with this idea either, but the state and the Vermont Rail System sat down with the top brass and worked out a deal where yes the line would be transferred to the state, and operated by a joint subsidiary of the Central Vermont & Vermont Rail System, with PV&T overhead rights between Wells River & White River Junction.
Thus the Newport Southern Joint Line; most traffic on the line is operated by the Vermont Rail System, but the PV&T uses it as a dieselized secondary to relieve traffic congestion on the Central Vermont and the PV&T’s Montréal main. The VTR gets most of the profits, the state of Vermont keeps this rail link alive, and the PV&T now has a Connecticut River secondary that ties the ex-CAR, the Montréal main, and the Albany main together.
The CV & VTR share power & MOW responsibilities, and have managed to improve the line so it once again supports 40mph trains.