Park at the Greenbelt Metro Station then fly BWI via theB30 route from Greenbelt station. Multi-day parking is available at the Greenbelt station.
The service is run by WMATA and was started on Tuesday November 13, 2001.
For schedule information (in PDF format), please click here.
With convenience like this, why would anyone from the DC area whois flying, drive and park at BWI?