belt·way / ˈbeltˌwā/ • n. a highway encircling an urban area. ∎  (Beltway) [often as adj.] Washington, DC, esp. as representing the perceived insularity of the U.S. government: conventional beltway wisdom.

Beltway Washington DC, especially as representing the perceived insularity of the US government, from a transferred use by association with the ring road encircling Washington.
Beltway Bandit in US slang, a company or individual, frequently one employed by a US government agency, hired by a corporation to assist in securing government contracts.