I-81 at Harrisonburg Va is a nuisance much of the time, morning and evening commutes and the University make it tight. Pass through there midday or evening if possible.
Most major traffic accidents seem to be from Troutville (US 460) to Roanoke.
Depending on your clearance and time constraints, You may want to travel some of Skyline Dr. or the Blue Ridge Pkwy.
Verify your heights and clearances first.
edit, changed to nuisance from nightmare. I live in the middle of nowhere and for people used to congestion, its likely not that bad.