Illinois Statutes Chapter 225. Professions,Occupations and Business Operations § 440/3.15. National Highway System defined

§ 3.15. “National Highway System” is a designation provided to certain highways by the Department, which designation must be approved by the United States Department of Transportation and the United States Congress for the purpose of providing an interconnected system of principal arterial routes that serve major population centers, international border crossings, ports, airports, public transportation facilities, other major travel destinations, and interstate and interregional travel and meet national defense requirements.