|Greenbelt–BWI Thurgood Marshall Airport Line|
Route B30 at BWI Business District station
|Operator||Washington Metropolitan Area Transit Authority|
Prince George's County|
Anne Arundel County
|Landmarks served||BWI Business District station |
|Start||Greenbelt station |
|Via||Capital Beltway, Interstate 95, Metropolitan Boulevard |
|End||BWI Marshall Airport |
|Length||Northbound: 30.7 miles (49.41 km) |
|Weekend frequency||No Service|
|Operates||6:00 AM – 10:30 PM (weekdays) |
|Cash||Exact change required|
|Timetable||Greenbelt-BWI Thurgood Marshall Airport Express Line|
The Greenbelt–BWI Thurgood Marshall Airport Express Line (commonly shortened to the Greenbelt–BWI Airport Line), designated Route B30, is a weekday-only bus route operated by the Washington Metropolitan Area Transit Authority between Baltimore-Washington International Thurgood Marshall Airport and the Greenbelt Metro Station of the Green Line of the Washington Metro.  The line operates every 60 minutes five days a week along the Baltimore-Washington Parkway between these two locations with no intermediate stops, with the exception of the BWI Business District Light Rail Stop,  and the last bus leaving BWI at 10:01 pm. The trip is approximately 29 minutes long. 
The line is unique for being the only WMATA bus line that has a connection with any Maryland Transit Administration non-commuter services, and is responsible for providing a regular link between the two services. The original $3 one-way fare was seen as a bargain compared with other transportation modes in the area, including Greyhound and MARC Train Service.  On June 25, 2017, the one-way fare was increased to $7.50 and weekend service was eliminated, making the B30 bus a more expensive option than the MARC train. 
The B30 line is also partly responsible for BWI Airport ranking as one of the nation's top 10 airports in ease of access.  WMATA also provides higher levels of service on the line in special times of need, especially on certain holidays. 
The state of Maryland, which provides funds for operating the service, has been criticized for doing little to promote its use. 
- "Greenbelt–BWI Thurgood Marshall Airport Express Line (B30)" (PDF). Washington Metropolitan Area Transit Authority. June 29, 2014. Retrieved January 4, 2017.
- Google (December 5, 2016). "Route B30" (Map). Google Maps. Google. Retrieved December 5, 2016.
- Elise H. Ford (2009). Frommer's Portable Washington, Part 3. Wiley Publishing, Inc. p. 12. ISBN 978-0-470-38433-6.
- Dresser, Michael (February 12, 2007). "Obscure Third Way Connects Baltimore and Washington". Baltimore Sun. p. 1.B. Retrieved March 20, 2011.(subscription required)
- "Be Ready for Metro Changes June 25th, 2017" (PDF) (Press release). WMATA. June 25, 2017. Retrieved June 26, 2017.
- Scott Dance (August 15, 2007). "BWI passenger access draws industry praise". Baltimore Business Journal.
- "Metro to have additional buses and trains on standby in anticipation of Thanksgiving week travel to regional airports" (Press release). WMATA. November 17, 2010. Retrieved March 20, 2011.