A(n) (obvious) solution for the Mount Vernon Trail crossing of George Washington Parkway
The regional cycling blog Washcycle has devoted many entries (including George Washington Memorial Parkway Action Plan) to the problems with how the Mount Vernon Trail in Northern Virginia crosses the George Washington Parkway and this creates "conflicts"-resulting in accidents and injuries--between bicyclists and motor vehicles.
In the previous entry, in the video showing the Dutch cycle highway, the sequence beginning around 2:45 demonstrates a perfect solution for the problems with the intersection of the Mount Vernon Trail and the George Washington Parkway in Virginia. Screen captures from a video by Mark Wagenbuur.
It's not that it isn't obvious without such an illustration, but prioritizing bicycle movement is so "foreign" to thinking by U.S. transportation planners, even if they work for the National Park Service, that such a choice is not being made.