70 ILCS 5/14.1
An Authority may secure the necessary funds to finance part or all of the cost of (i) acquiring, establishing, constructing, developing, expanding, extending or further improving a public airport, public airports, or airport facilities within or without its corporate limits or within or upon any body of water adjacent thereto; and (ii) studying, designing, acquiring, constructing, developing, expanding, extending, or improving any rail facility or related facility as provided in this Act for a Rail Authority established by the Board of Commissioners of the Authority, upon a determination by the Board of Commissioners, that, in its judgment, the rail or other service to be provided by those rail facilities or related facilities will benefit the airport operated by the Airport Authority, through the issuance of bonds as hereinafter provided in Sections 14.1 to 14.5 inclusive, to the principal amount of which at any one time outstanding, together with other outstanding indebtedness of the Authority, shall not exceed 2.3% of the aggregate valuation of all taxable property within the Authority, as equalized or assessed by the Department of Revenue or, until January 1, 1983, if greater, the sum that is produced by multiplying the Authority's 1978 equalized assessed valuation by the debt limitation percentage in effect on January 1, 1979. No such airport project shall be financed by the issuance of bonds under this Section unless such proposed airport project has been approved by the Department of Transportation as to location and size and found by the Department to be in the public interest; provided that the approval of the Department of Transportation as provided in Sections 14.1 through 14.5 is not required in the case of airport projects consisting solely of commercial or recreational facilities or rail facilities or related facilities.
70 ILCS 5/14.1