Control Area

A controlled airspace extending upwards from a specified limit above the earth. (FAA4)

(As it pertains to the Interstate Highway System) A metropolitan area, city or industrial center, a topographic feature such as a major mountain pass, a favorable location for a major river crossing, a road hub which would result in material traffic increments on the Interstate route, a place on the boundary between two States agreed to by the States concerned, or other similar point of significance. (23CFR470)