Originally Posted by Annandaler

United flights SFO-IAD come to either C or D gates (C/D is one very long building). If you come to one of the C gates, follow the overhead signs for "Gates A, B, ....", which will lead you to the train, and then one stop on the train to the A concourse where QR is. If you come to one of the D gates, follow similar signs, which will lead you to the Mobile Lounge docking area. Take the right-most Mobile Lounge to the A Concourse. If the D-to-A Mobile Lounge isn't running at that time, take the D-to-Terminal Mobile Lounge and then follow the signs to walk or take the train to A Concourse.

All of this is post security.