Immediately past the New River, the freeway becomes the border between Montgomery County to the southeast and the independent city of Radford to the northwest, where it interchanges with SR 232/SR 605. From this point, I-81 fully enters Montgomery County, coming to rest areas in both directions prior to an interchange with SR 177/SR 600, which also provides access to Radford University.
Immediately past the New River, the highway transitions into a boundary separating Montgomery County to the southeast from the independent city of Radford to the northwest, where it merges with SR 232/SR 605. From this point, I-81 fully enters Montgomery County, stopping at rest stops in both directions prior to an interchange with SR 177/SR 600, which also provides access to Radford University.