Amtrack

www.amtrak.com

Service stations in Virginia: close to metro stations – Union Station, Alexandria, and Franconia Springfield; further away - Fredericksburg, and Manassas; (can then continue on VRE train (weekdays service only) to get to metro stations); Woodbridge (from that area you can then use PRTC bus service (weekdays only) to get to metro stations). Lorton, VA is an auto train only station, the only service is non-stop service from Sanford, FL (SFA).
 
Service stations in Maryland: BWI Airport (from there you can use shuttle metro bus B30 (cost $3.10, weekdays and weekends, check schedule to get to closest metro station, Green Line); New Carrollton (walking distance to metro station, Orange Line)
Schedules/Fares/Tickets: plan your trip and purchase tickets here.