Clara Barton Parkway in the context of "Divided highway"

A dual carriageway (BrE) or a divided highway (AmE) is a class of highway with carriageways for traffic travelling in opposite directions separated by a central reservation (BrE) or median (AmE). Roads with two or more carriageways which are designed to higher standards with controlled access are generally classed as motorways, freeways, etc., rather than dual carriageways.

A road without a central reservation is known as a single carriageway regardless of how many lanes there are. Dual carriageways have improved road traffic safety over the years and over single carriageways and typically have higher speed limits as a result. In some places, express lanes and local or collector lanes are used within a local-express-lane system to provide more capacity and to smooth out traffic flows for longer-distance travel.

The Capital Beltway, designated as Interstate 495 (I-495) for its entire length, is an auxiliary Interstate Highway in the Washington metropolitan area. The 64-mile (103 km) beltway encircles Washington, D.C., the capital of the United States, and its inner suburbs in adjacent Maryland and Virginia. It also passes through the capital, near the western end of the Woodrow Wilson Bridge over the Potomac River; Prince George's and Montgomery counties in Maryland and Fairfax County; and the independent city of Alexandria in Virginia.

The route is the basis of the phrase "inside the Beltway", used when referring to issues dealing with U.S. federal government and politics. Its southern and eastern half runs concurrently with I-95. It was constructed in 1964. The Cabin John Parkway, a short connector between I-495 and the Clara Barton Parkway near the Potomac River along the Maryland–Virginia border, is considered an Interstate spur (I-495X) by the Maryland State Highway Administration (MDSHA).