Question: What is the busiest airport in the region including  Central Maryland and Northern Virginia?

<P0-S0> Baltimore/Washington International Thurgood Marshall Airport (IATA: BWI, ICAO: KBWI, FAA LID: BWI) is an international airport located in Linthicum in northern unincorporated Anne Arundel County, Maryland. <P0-S1>  The airport is 9 miles south of downtown Baltimore and 32 miles northeast of Washington, D.C. It is the busiest, by passenger count, of three major airports serving the Baltimore–Washington metropolitan area in the United States, the other two being Ronald Reagan Washington National Airport and Washington Dulles International Airport. <P0-S2>  It is commonly referred to as BWI or BWI Marshall. <P0-S3>  The airport is named after Thurgood Marshall, a Baltimore native who became the first African American to serve on the Supreme Court of the United States. <SEP> <P1-S0>  The region includes Central Maryland, Northern Virginia, three counties in the Eastern Panhandle of West Virginia, and one county in South Central Pennsylvania. <P1-S1> The Baltimore–Washington metropolitan area is a combined statistical area consisting of the overlapping labor market region of the cities of Washington, D.C. and Baltimore, Maryland. <P1-S2>  It is the most educated, highest-income, and fourth largest combined statistical area in the United States. <SEP> <P2-S0> WDCH-FM (99.1 FM; "Bloomberg 99.1 and 105.7 HD2") is a radio station currently broadcasting a business news format. <P2-S1>  Licensed to the eastern suburb of Bowie, Maryland, in Prince George's County, it serves the central Maryland and northern Virginia metropolitan areas of Baltimore, Maryland/Washington, D.C. region. <P2-S2>  The station is currently owned by CBS Radio and operated by Bloomberg L.P. Its transmitter is located near Crofton, Maryland in suburban central Anne Arundel County to the east, and the broadcasting studios are located near the Washington Navy Yard along the north/west bank of the Anacostia River (Eastern Branch of the Potomac River) in Southeast Washington. <P2-S3>  WDCH-FM often airs D.C. United soccer and Washington Wizards pro basketball games in the NBA due to sister station WJFK-FM, 106.7 "The Fan" usually already covering a game elsewhere. <SEP> <P3-S0> The Maryland Transit Administration (MTA) is a state-operated mass transit administration in Maryland, and is part of the Maryland Department of Transportation. <P3-S1>  It is better known as MTA Maryland to avoid confusion with other cities' transit agencies who share the initials MTA. <P3-S2>  The MTA operates a comprehensive transit system throughout the Baltimore-Washington Metropolitan Area. <P3-S3>  There are 80 bus lines serving Baltimore's public transportation needs, along with other services that include the Light Rail, Metro Subway, and MARC Train. <P3-S4>  With nearly half the population of Baltimore residents lacking access to a car, the MTA is an important part of the regional transit picture. <P3-S5>  The system has many connections to other transit agencies of Central Maryland, Washington, D.C., Northern Virginia, and south-central Pennsylvania (Hanover, Harrisburg, and York): WMATA, Charm City Circulator, Regional Transportation Agency of Central Maryland, Annapolis Transit, Rabbit Transit, Ride-On, and TransIT.