Where exactly were you when you saw the overpass?
There are no railroads going over I-80 in the vicinity of the highest point east of the Mississippi, near where PA 153 crosses I-80 [Penfield exit]. The old NYC line down the West Branch of the Susquehanna between Clearfield and Keeting passes under I-80 about 10 miles east of this location near Clearfield, and the old AVRR Low Grade line, and the old B&S line pass under I-80 about 10 miles west of this location near the Sabula exit.
The only overpass that I am aware of in the area is the Pittsburg & Shawmut line, which passes over I-80 about halfway between Hazen and Reynoldsville exits, west of Mill Creek.
Dan