Columbia subject headings:
Air quality management--Government policy--United States.
Air quality--Standards--United States.
International Surface Transportation Efficiency Act of 1991.
Transportation and state--United States.
Transportation--Environmental aspects--United States.
United States. Clean Air Act Amendments of 1990.
Harvard subject headings:
Air quality management--Government policy--United States
Air quality--Standards--United States
Transportation and state--United States.
Transportation--Environmental aspects--United States
Princeton subject headings:
Air quality management--Government policy--United States.
Air quality--Standards--United States.
Transportation and state--United States.
Transportation--Environmental aspects--United States.