Originally Posted by djp98374

You can take the subway/ metro between Dulles snd national in about 75 minutes . Dulles to roslyn is about 45 min, transfer to blue 10-15 min, 15-20 min to national. Both stations are at the main terminal so not long of a walk. You can take a cab which is about 30-60 minutes depending on when in the day.

there is no bus route for the public. There likely is something for airport staff and crew. Especially during the 9 pm-9 am time when subway line is not running.

dulles is a United hub, National is an American hub Dulles gets 95% of international flights. AA and AC has flights to eastern Canada and AA has flight to Bahamas/ northern Caribbean

AA/DL partners can fly into Dulles and thrn make a connection thru DCA while AC can fly to national connecting to a Dulles international flight. WN has limited service out of Dulles ( direct to DEN, MDW) while DCA/BWI has flights elsewhere

you can get similar routes in NYC flying into EWR/JFK and out of a different airport or LGA.