50 ILCS 25/1
It is hereby found and declared that public agencies of the State, with regard to certain existing and proposed public improvements and developments, are not able to make the most effective utilization of the land acquired or to be acquired for such public improvements and developments because of the nature of such public improvements and developments. It is further found and declared that the scarcity and high cost of available land in many areas of the State where public improvements and developments are needed, coupled with the inability to make a more effective utilization of the land, from both a planning and economic viewpoint, because of the nature of some public improvements and developments, render it necessary and desirable that, where feasible, air rights over existing and proposed public improvements be sold or leased and that such public improvements and developments be constructed or developed in combination with other compatible desirable and lawful uses constructed on such air rights sold or leased to private interests, thereby reducing the cost of such public improvements and developments; making a more effective utilization of land from both a planning and economic viewpoint and placing the non-public portion of any such improvement back on the tax rolls.
50 ILCS 25/1