Chicago, Illinois, is the third-largest city in the United States and a world transit hub. The area is served by two major airports, numerous highways, elevated/subway local train lines, and city/suburban commuter rail lines; it is the national passenger rail hub for Amtrak routes, and also the main freight rail hub of North America.
Surface transportation networks and public ways within the city are the responsibility of the Chicago Department of Transportation. Mass transit in much of the Chicago metropolitan area is managed through the Regional Transportation Authority (RTA), which was installed by a referendum in 1974. The RTA provides transportation services through the funding of three subordinate agencies: the Chicago Transit Authority, Metra, and Pace. Operation of the city's airports is the responsibility of the Chicago Department of Aviation.