Never been to Virginia myself but big black cats turning up near parkways and trails is something I follow pretty closely. We get similar reports over here in the UK - big cats in Herefordshire and the Welsh borders, usually melanistic leopards or black pumas according to most researchers.
The thing that always strikes me with these sightings is how consistently people describe the movement. That low fluid walk, the long tail. People dont mistake a dog for that.
What size are we talking roughly? And was it crossing the road or just spotted in the tree line? Those details matter a lot for working out what it actually was. Would love to hear more from anyone else who saw something out there.