Maryland's Interstate highways include I-95, which enters the northeast portion of the state, goes through Baltimore, and becomes part of the eastern section of the Capital Beltway to the Woodrow Wilson Bridge. I-68 connects the western portions of the state to I-70 at the small town of Hancock. I-70 continues east to Baltimore, connecting Hagerstown and Frederick along the way. I-83 connects Baltimore to southern central Pennsylvania (Harrisburg and York, Pennsylvania). Maryland also has a portion of I-81 that runs through the state near Hagerstown. I-97, fully contained within Anne Arundel County and the shortest one- or two-digit Interstate highway outside of Hawaii, connects the Baltimore area to the Annapolis area.
There are also several auxiliary Interstate highways in Maryland. Among them are I-695, the McKeldin (Baltimore) Beltway, which encircles Baltimore; a portion of I-495, the Capital Beltway, which encircles Washington, D.C.; and I-270, which connects the Frederick area with the Washington area. The Capital Beltway is currently heavily congested; however, the ICC or Intercounty Connector, which may begin construction in 2006 or early 2007, could be the beginning of an outer, second beltway. Construction of the ICC was a major part of the campaign platform of former Governor Robert Ehrlich, who was in office from 2003 until 2007.
Maryland also has a state highway system that contains routes numbered from 2 through 999, however most of the higher-numbered routes are either not signed or are relatively short. Major state highways include Routes 2 (Governor Ritchie Highway/Solomons Island Road), 4, 32, 100, 295 (Baltimore-Washington Parkway), 355, and 404.
Maryland's largest airport is Baltimore-Washington International Thurgood Marshall Airport (formerly known as Friendship Airport and recently renamed for former Supreme Court Justice Thurgood Marshall, who was born in Baltimore). The only other airports with commercial service are at Hagerstown and Salisbury. The Maryland suburbs of Washington, D.C., are also serviced by the other two airports in the region, Ronald Reagan Washington National Airport and Dulles International Airport, both in Northern Virginia. For the year to date, BWI Thurgood Marshall Airport has received the highest number of passengers out of all the airports in Baltimore-Washington Metropolitan area.
Amtrak trains serve Baltimore's Penn Station, BWI Airport, New Carrollton, and Aberdeen along the Northeast Corridor. In addition, train service is provided to Rockville and Cumberland on the Amtrak Capitol Limited. MARC trains, operated by the State's Transit Authority, connect nearby Washington, D.C. and Baltimore, and other towns. The Washington Metro subway and bus system serve Montgomery County and Prince George's County. The Maryland Transportation Authority's light rail and subway system serve Baltimore City and adjacent suburbs.
Source: Answers.com, Wikipedia, and Maryland.gov