Maryland Route 4

Maryland Route 4

Maryland Route 4 (MD 4) is a state highway in the U.S. state of Maryland. The state highway runs 64.85 miles (104.37 km) from MD 5 in Leonardtown north to Southern Avenue at the Washington, D.C. border, past which the highway continues as Pennsylvania Avenue. MD 4 is a major commuter route in Southern Maryland, connecting Washington and suburbs in Prince George's County, Anne Arundel County, and Calvert County. MD 4 also connects residential communities in southern Calvert County with employment centers in St. Mary's County, including Naval Air Station Patuxent River. In conjunction with U.S. Route 301 (US 301) and MD 2, MD 4 also provides interregional connections with Baltimore and Annapolis, respectively. MD 4 is part of the National Highway System between MD 235 in California and its northern terminus.

MD 4 heads east from Leonardtown as St. Andrew's Church Road and then Patuxent Beach Road east of MD 235. The state highway crosses the Patuxent River on the Governor Thomas Johnson Bridge between California and Solomons, then joins MD 2 north through Prince Frederick. At 27.40 miles (44.10 km), MD 2/MD 4 is the longest state-numbered highway concurrency in Maryland. MD 4 and MD 2 separate at Sunderland, with MD 4 heading northwest as Southern Maryland Boulevard to Bristol, Maryland. In Bristol in Anne Arundel County, MD 4 continues as the Stephanie Roper Highway to a second crossing of the Patuxent River near Upper Marlboro. In Prince George's County at Water Street, the state highway heads west as Pennsylvania Avenue toward Washington.

MD 4 is one of the original Maryland state highways. The state highway followed roughly its present alignment through Prince George's County, then headed east through Anne Arundel County along what is now MD 408. In the 1960s, MD 4 took over MD 416 (Southern Maryland Boulevard) southeast to Sunderland and joined MD 2 all the way to Solomons. After the Governor Thomas Johnson Bridge opened in the late 1970s, MD 4 was extended west from Solomons to Leonardtown. MD 4 has been upgraded to a divided highway for most of its length, beginning in the early 1960s from Washington, reaching Solomons in the mid 1980s, and expected to continue into St. Mary's County in the 2010s.