The presence of two different state route networks- primary state routes (prefixed by 'VA' on OSM, numbered 599 and below) and secondary states route (prefixed by 'SR' on OSM, numbered 600 and above and equivalent to county routes seen in other states)- rarely ever dictate the classification of roads, as primary state routes' classifications can range from freeways like VA 267, the Dulles Toll Road, all the way down to access roads like VA 399 at the Virginia Museum of Science. 

Secondary state routes, which account for nearly every other road in Virginia minus those in cities and some counties and privately-maintained areas, are loosely classified in a similar way too, as the majority of them are residential streets, collector roads, or rural farm roads but can often times be major thoroughfares or even expressways like SR 606/607 northwest of Dulles or the aforementioned Belmont Ridge Road, which jumps between tertiary, secondary, and primary in different places.

It would be quite difficult to have a road classification scheme based on highway numbers in Virginia (or anywhere in the US really) for those particular reasons.