Hello, a while back I downgraded this section to primary because it is a scenic parkway that doesn't allow trucks and is closely paralleled by the more-important US 1, therefore not making it a trunk road. It should be worth noting that the highways around Virginia and Washington DC are classified based on their importance rather than their physical construction. Trunk roads in this case are non-freeways that serve as connectors between two destinations of significance rather than just expressways (which are now indicated by expressway=yes tags). 

For example, VA 28 has some expressway and even freeway sections (which are tagged with expressway=yes and highway=motorway respectively), but is also a surface street through Manassas or a two-lane rural highway. It does meet the criteria for trunk however as it links places like Herndon and Manassas towards Culpeper and Charlottesville.

Another example is Fairfax County Parkway which is fully expressway/freeway, but the reason it does meet trunk criteria is due to it being a major highway that carries traffic travelling between Woodbridge/Lorton and Fairfax/Reston.

The non-freeway sections of GWMP do seem like good candidates for trunk classification considering they are major commuter routes and bypass some of the Alexandria sprawl, but it's mainly intended to be a scenic bypass and lacks a full interchange with the Beltway and does not allow heavy traffic, each of which would be more convincing to make it a trunk route (and it certainly would be one if that were the case, and Us 1 would be the primary route), but for those reasons it's better as primary.