The St. Lawrence Seaway Project was also a major contributor to the decline on the Northern because both Boston and Portland were major transshipment ports for grain -- primarily Canadian -- enroute to Europe. When the Project was completed, grain could be shipped via a year-round, ice-free, riverine and maritime routing. The grain elevators at both Boston and Portland that had provided infrastructure for winter shipments quickly shut down, and income -- thus justification for a high standard of maintenance -- began to disappear. When passenger service was cancelled, there was no justification for that high level of maintenance. I-89 and I-93 made the decline complete.
As testimony to the quality of the track back in passenger days, I took CN-CV out of Montreal's Gare Centrale back to Nashua Street in 1960, following a CN steam excursion. At WRJ, we changed to Budds, and I clocked the transit mp-to-mp through Tyngsborough Curve at 75, a bit above the authorized.
On the subject of "authorized," if you have any older B&M ETTs, check out the variations in authorized tonnage on the Northern. This was neither an easy nor economical stretch of railroad to run, no matter its beauty.
"A gray crossover is definitely not company transportation."