Between its intersection with Sudley Road (Virginia State Route 234 (Business)) northwest of Manassas and its termination at Interstate 81 west of Front Royal, Interstate 66 follows a route similar to that of the railroad, crossing the railroad twice. The railroad's route is also similar to that of Virginia State Route 55, which it crosses several times. The railroad and the two highways cross the Bull Run Mountains at Thoroughfare Gap, near the historic Beverley Mill and Broad Run.