I managed to get north of highway 267 on today's run, a first for me. So yes, you do have to take the other trail where the sign says 'trail redesign, take this trail'. The highway underpass is pleasant, nothing that you'd want to avoid.
I got to the Leesburg Pike but then, not quite knowing where I was, went west and not east. Eventually I'll want to go east at the Leesburg Pike, to end up at the Potamac by Great Falls National Park. 16 miles out and back today. Good fall weather, very pleasant. Still, I ended feeling totally wiped out in the late afternoon, a few hours after the run. Not clear what's going on, I suspect yesterday's hill intervals may have constributed, a slow 16 miles shouldn't do this.