Intersection of Washington and Old Dominion (W&OD) Railroad Trail and I-66 Custis Trail. W&OD Trail travels in W&OD Railroad Regional Park for 45.5 miles between Alexandria-Arlington border near Shirlington to Purcellville, VA, along former route of W&OD Railroad from old-town Alexandria to Bluemont, VA. Custis Trail follows I-66 to Rosslyn in Arlington, following routes of former Arlington-Fairfax Railway (electric trolley line) between Falls Church and Ballston and W&OD Railroad between Ballston and Rosslyn.