You could also use the Crystal City VRE station, then take Crystal Dr to Long Bridge Dr to Boundary Channel to the 27 Trail to the Mt Vernon Trail. Take the Key Bridge into DC and either cut through Gtown’s campus, or take surface streets to American. Not knowing exactly where you’re going, it looks to roughly the same distance, but possibly faster because less city stop-and-go.
I’ve never noticed before, but it looks like there’s a dirt path in a park labeled “Whitehurst Parkway” that would cut some distance if you went through Georgetown.