Alcoman,
This will almost be in your eye all the way to Vandalia.
Starting in Hornell on West St. by the overhead bridge. at the wye where the WNYP meets the NS line. North tracks are the NS line to Portage/Buffalo.
Follow Rt 21 towards Andover. Railroad will be to your left to the ALmond dam. Then will be out of your eyesight till your past the Alred Almond school. It will reappear to your left at the scene of that bad wash out they fixed a year ago. Then goes by Buffalo Crushed Stone and Hi Tech on towards Andover, crosses overhead by Whitfords in Alfred Station and will stay on your right till after you have turned onto RT 417 west. A new overhead bridge was put in by the state in the 80's west of Andover, and the tracks follow then to your right as you go into Wellsville. There are various side streets you can cruise to look over the line. Note the Depot building is still in existance, Corner of Loder and Pearl St. The former Freight depot was sold to Harris Supply which is still there. There are two old metal boxcars sitting on the northend as storage units. There are two or three sidings here, but I think only one is considered active, the rest I am sure need rehabed.
Follow Rt 19 North to Belevedere and follow the county road to Friendship. This runs next to the tracks all the way to Cuba. Hope on to I86 west and go to Olean, and there are various city streets you can follow the line thru to the yard. The Main is the far side of the yard. It goes into Allegany NY and you can follow Rt 417 all the way to Salamanca, at times view will be obsured due to tracks vs. river vs highway. after Salamanca it gets hard to view due to the resevoir.
I hope this will help you. Its a nice Sunday drive. But, definantly not as the crow flies.
~Greg Graves