Originally Posted by ND76

You are going to be looking at about 30 minutes on the metro between Bethesda and Union Station, then about 35 minutes on the MARC train (a bit less if you go on Amtrak). Here's the MARC schedule (MARC trains only run Monday through Friday and not on weekends or holidays):

http://mta.maryland.gov/sites/defaul...nn_Nov2011.pdf

Here is another way to BWI on public transit that runs 7 days a week that you may not have considered. Take the Metro in the northbound direction, to the end of the line at Shady Grove. There is a new public bus, Route 201, that runs to BWI airport along the new Inter-County Connector toll road.

http://www.mtaiccbus.com/route201.html#mapsa

I saw this bus at BWI Wednesday night and it is a large new inter-city style coach, not a street bus.

This looks to be a little bit longer; however, this bus will drop you off at the BWI terminal--if you take the train, the BWI train station is at least 2 miles from the air terminal, and you have to wait for a shuttle bus, which may or may not be sitting outside the BWI train station when you arrive, then takes at least 10 minutes to drive over to the airport.

Enjoy your trip.