Bob:
That overpass over Rte 20 at 84 Lumber is not the same line we're talking about here--not even the same railroad.
The two bridges you see over Rte 20 are the CSX "Selkirk Branch", which is actually the main line for freights from Chicago, Buffalo, etc to the east coast. All CSX mainline traffic to New Jersey or New Enbland, except for the Amtrak passenger trains, passes here.
The D&H line in question diverges at Cole Road, the east end of the village of Delanson, about a mile south of Route 20, then heads southeast towards Voorheesville. Crosses under NY Route 7 about a mile east of Duanesburg.
This line will look a lot more heavily used at Cole Road than it will farther down the line. It's frequently used right at Cole Road for stashing MW equipment, so the first 20 car lengths see use pretty often. Beyond that, it's "as needed" down to Voorheesville, and that ain't needed very often.