Ok, acknowledging this is more of an art than a science and that you have more experience with highway tagging in Virginia than me, I guess my confusion comes partially from wondering why every GWMP section north of the DCA interchange is classified as motorway, and yet this section was primary. The physical characteristics of those sections are identical to this one, and there is no population center on the north end and I would argue of equal "importance." Also confused how a motorway can transition directly into a primary road with no discernible physical difference or having passed a population center of importance. 

The GWMP strikes me as comparable to the Suitland Parkway across the Potomac in almost every way, which is tagged as trunk throughout. Anyway, I don't feel all that strongly but happy to discuss more.