I believe the original statute enacted in 1932 has been shuffled around and revised, probably a number of times since then.  The present applicable Code section is as follows:  "33.2-105.  Evidence as to existence of public highway.   

     When a way has been worked by highway officials as a public highway and is used by the public as such, proof of these facts shall be prima facie evidence that the same is a public highway.  And when a way has been regularly or periodically worked by highway officials as a public highway and used by the public as such continuously for a period of 20 years, proof of these facts shall be conclusive evidence that the same is a public highway.  In all such cases, the center of the general line of passage, conforming to the ancient landmarks where such exist, shall be presumed to be the center of the way and in the absence of proof to the contrary, the width shall be presumed to be 30 feet.

      Nothing contained in this section shall be construed to convert into a public highway a way of which the use by the public has been or is permissive and the work thereon by the highway officials has been or is done under permission of the owner of the servient tenement."