Maintenance area means any geographic region of the United States that the Environmental Protection Agency (EPA) previously designated as a nonattainment area for one or more pollutants pursuant to the Clean Air Act Amendments of 1990, and subsequently redesignated as an attainment area subject to the requirement to develop a maintenance plan under section 175A of the Clean Air Act, as amended (42 U.S.C. 7505a).
23 CFR § 450.104
Unless otherwise specified, the definitions in 23 U.S.C. 101 and 49 U.S.C. 5302 are applicable to this part.