It was likely directing them out the Dulles access road, which will fly compared to any other road during rush hour. But it's not legal to take that unless you're going to the airport. In the past, I severed all entrances and exits to the airport property with a small segment of parking lot to prevent any routing through the airport. However, it looks strange to see the freeway suddenly turn into a parking lot, so a well meaning editor took those out a while back. If others agree that a parking lot segment is the best solution, then it should be added by high level editor and locked to make sure it doesn't get undone in the future.These are the segments
that I would have changed to include a small parking lot segment. Ariane Way on the north and a single ramp segment from the Greenway and 28N are the only segments that remain, which means that anyone just to the north likely gets routed around to 28 instead of taking this back entrance, and anyone from the south is probably getting directed to pass the airport and take a U-turn. I'm also not clear on why there are several street segments instead of ramp segments on the south side of the access road.