Beltway

[Greta]

Nickname for the highway ([I-495]) that encircles Washington DC through the surrounding states of Virginia and Maryland.

A defining feature of your DC-respective locale is whether it is inside or outside [the beltway].

[Inside the beltway] can also refer generically to politics in the US capital city.

[Gregory]

A highway encircling an urban area.

[Sonia]

a main road that goes around the edge of a town, allowing traffic to avoid the town centre