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Chicago, Illinois is the third-largest city in the United States and a major transportation hub. The city is served by two major airports, and is the main freight rail hub of North America.

Michael Hayden's neon installation "Sky's the Limit" (1987) in a subterranean walkway at O'Hare Airport. Sometimes called "The Gershwin Tunnel", the walkway connects concourses B and C of Terminal 1, which is operated by United Airlines.
A westbound 'L' train crosses the south fork of the Chicago River

Chicago, Illinois is the third-largest city in the United States and a major transportation hub. The city is served by two major airports, and is the main freight rail hub of North America.

Mass transit in much of the Chicago metropolitan area is managed through the Regional Transportation Authority (RTA), which was installed by referendum in 1974. The RTA provides transportation services through the funding of three subordinate agencies: the Chicago Transit Authority, Metra, and Pace.