50 ILCS 25/3
Whenever the nature of any existing or proposed public improvement or development does not, from both a planning and economic viewpoint, permit or lend itself to the full or efficient utilization of the land acquired or which is necessary to be acquired for the public improvement or development, the governing body of any public agency may, subject to such restriction as may be imposed by the governing body of the public agency for the development of a compatible, desirable and lawful combined occupancy structure not inconsistent with local laws, sell or lease the air rights over the existing or proposed public improvement or development to a developer on which to construct a combined occupancy structure. The non-public portion of any combined occupancy structure must be constructed in whole or in part over the existing or proposed public improvement. The sale or lease of such air rights by a public agency may be made subject to such restrictions relating to the time and condition of the vesting of title in such air rights as the governing body of the public agency may impose. Any developer who purchases or leases air rights from a public agency over an existing public improvement or development under the provisions of this Act must, as a condition of such purchase or lease, agree with the public agency to construct the non-public portion of a combined occupancy structure in accordance with the plan of development prepared by the developer and approved by the public agency and such agreement may be made a covenant running with the land and by ordinance or resolution of the governing body of the public agency shall be made a covenant running with the land. Any developer who purchases or leases air rights from a public agency over a proposed public improvement or development must, as a condition of such purchase or lease, agree with the public agency to construct or cause to be constructed both the public and non-public portions of a combined occupancy structure in accordance with: (1) the plan of development for the public portion of the combined occupancy structure prepared by the public agency and in accordance with the plan of development for the non-public portion of the combined occupancy structure prepared by the developer and approved by the public agency or (2) as the case may be, in accordance with the plan of development for both the public and non-public portions of the combined occupancy structure prepared by the developer and approved by the public agency, and such agreement may be made a covenant running with the land and by ordinance or resolution of the governing body of the public agency shall be made a covenant running with the land. The public agency shall by public notice by publication once each week for 2 consecutive weeks in a newspaper having general circulation in the territorial limits of the public agency prior to the execution of any contract to sell or lease air rights and prior to the delivery of any instrument of conveyance with respect thereto, invite proposals from and make available all pertinent information to developers interested in undertaking to purchase or lease air rights and to construct or cause to be constructed a combined occupancy structure, or any portion thereof. Such notice shall contain a description of the area of the existing or proposed public improvement or development; the details of the existing public improvement, or the details of the plan of development of the public portion of a combined occupancy structure if the public agency has prepared a plan of development of the public portion thereof; and, if the public agency has not prepared a plan of development for the public portion of a combined occupancy structure, then the detailed requirements of the needs to be met for the public portion of a combined occupancy structure sufficient to enable a developer to submit a plan of development for a combined occupancy structure including both the public and non-public portion of a combined occupancy structure, all of which the developer shall undertake in writing to carry out together with such further undertakings by the developer as the public agency may deem necessary to obligate the developer, his successors and assigns (1) to use the non-public portion of a combined occupancy structure for the purposes designated in the plan of development for a combined occupancy structure, which shall be a compatible, desirable and lawful non-public use complying with local law, (2) to commence and complete or cause to be commenced and completed the construction of the combined occupancy structure, or portion thereof, within the periods of time which the public agency fixes as reasonable and (3) to comply with such other conditions as are necessary to carry out the purposes of this Act. The public agency may negotiate with any developer for proposals for the sale and purchase or lease of air rights and shall consider all proposals submitted to it for the construction of a combined occupancy structure, or any portion thereof, and the financial and legal ability of the developers making such proposals to carry them out. The public agency at a public meeting, notice of which shall have been published in a newspaper of general circulation within the territorial limits of the public agency at least 15 but not more than 30 days prior to such meeting; may accept such proposal as it deems to be in the public interest and in furtherance of the purposes of this Act. The construction of the public portion of any combined occupancy structure shall be let upon open competitive bidding to the lowest responsible bidder. The sale or lease of air rights in accordance with the provisions of this shall be made at not less than fair use value. Periodic payments may be made by the public agency to the lowest responsible bidder selected by the public agency to construct the public portion of a combined occupancy structure as the work progresses. The developer who is selected to construct or to cause to be constructed a combined occupancy structure, or any portion thereof, shall furnish to or cause to be furnished to the public agency a performance and payment bond to serve as security for the faithful performance of the contract for the construction of the combined occupancy structure, or any portion thereof, and for the payment of all persons, firms or corporations to whom the developer or contractor may become legally indebted for labor, materials, facilities or services of any nature, employed or used by the developer or contractor in performing the work, such bond to be in such amount and with such surety as may be approved by the public agency.
50 ILCS 25/3