MARC train to DC, Metro to Airport

There are two MARC train lines that go from Baltimore to DC: The Penn line is the main one, it goes from Penn Station to DC via New Carrollton, and runs every day with decent enough frequency.

The Camden line is the other option, it runs limit rush-hour-only service between Camden Yards and DC via Greenbelt/College Park. It is slower than the Penn line, but depending on your location in Baltimore and timing of your flight might be easier to get to.

For both lines, the fastest way to the airport is ride to Union Station, then take the Red Line to Metro Center, and change to the blue line for National Airport.

For the Penn line, if you don’t want to deal with changing at Metro center, you can also get off at New Carrollton and catch a blue line train directly to National airport, tho it will take longer than the Union Station option.

Normally if you took the Camden line you’d be able to catch a direct yellow line at Greenbelt or College Park, but the entire yellow line is currently closed for repairs to the bridge over the Potomac, so if you do the Camden line it’s easiest to just go all the way to Union.

Also, normally there wouldn’t be any blue line trains at New Carrollton, but due to the Yellow line construction, blue line service was significantly beefed up, with every other blue line train going to New Carrollton instead of Largo.

Lmk if you have any questions.