Boston, Hoosac Tunnel and Western and Southern Vermont?

The Boston, Hoosac Tunnel and Western Railway built the line from Rotterdam Junction into southwestern Vermont. The Troy and Boston Railroad (New York) and Southern Vermont Railroad (Vermont) built the line from Troy into Vermont. From what I can tell, on the Massachusetts side, it was only the Troy and Greenfield Railroad. It looks like the Fitchburg bought/merged all of these in 1887.

My question is where the two parallel lines originally merged into one. At the state line, there are two separate lines (the south one is the BHT&W, the north one the T&B/SV). From there to a point in Williamstown, the present line is double-tracked. nhtopos isn't useful for this, as it shows two tracks becoming one on the border of a quad (meaning there was probably laziness involved). Any help?

Also posted in the New England forum.

I think that the two lines came together in Vermont, right about at the state line(w/ NY). They had separate right of ways. I have explored this especially in the Hoosick Falls area. The two lines crossed at the station there. It was an over under. This made for left hand running to Johnsonville.
The Fitchburg got control of both lines. As I stated above, each line was used as half of a double track arrangement.

From what I've found out since I posted the question, Massachusetts owned the whole Troy and Greenfield Railroad, from the Vermont state line to Greenfield, after the company defaulted on their loan in 1862 while building the Hoosac Tunnel. It appears that the Troy and Boston Railroad leased the Southern Vermont Railroad, but I also see something about the T&G buying it in 1860. Maybe that was cancelled with the bankruptcy? (search here for "Troy & Boston Railroad")

Anyway, assuming the T&B leased the SV, they both had their own lines to the VT/MA state line, where they merged into the state's line, which was usable at a fixed cost. The Fitchburg Railroad bought both companies in 1887, ending the rivalry - prior to that they likely both interchanged with the Fitchburg.