MONTGOMERY COUNTY, Va. – UPDATE
The wreck is now cleared.
The Virginia Department of Transportation says traffic is backed up 3 miles on Interstate 81 southbound after a tractor-trailer crash.
The crash is centered at mile marker 106.9 in Montgomery County. That's closest to the Radford exit. The south left shoulder and left lane are closed.
We'll be updating this story as we learn more from VDOT.