Va. Code § 46.2-1122
For the purposes of this article the following terms shall have the following meanings, unless the context clearly indicates otherwise:
"Single axle" means an assembly of two or more wheels whose centers are in one transverse vertical plane or may be included between two parallel transverse vertical planes forty inches apart, extending across the full width of the vehicle.
"Tandem axle" means any two or more consecutive axles whose centers are more than forty inches but not more than ninety-six inches apart, and are individually attached to and/or articulated from a common attachment to the vehicle including a connecting mechanism designed to equalize the load between axles.
"Single axle weight" means the total weight transmitted to the highway by all wheels whose centers may be included between two parallel transverse vertical planes forty inches apart, extending across the full width of the vehicle.
"Tandem axle weight" means the total weight transmitted to the highway by two or more consecutive axles whose centers may be included between parallel transverse vertical planes spaced more than forty inches and not more than ninety-six inches apart, extending across the full width of the vehicle.
"Group of axles" means any two or more consecutive axles located under a vehicle or combination.
Va. Code § 46.2-1122