605 ILCS 5/4-303
Investigations made by the Department to determine the reasonably anticipated future need for federal aid highways and State highways may include, but shall not be limited to, the making of traffic surveys, the study of transportation facilities, research concerning the development of the several areas within this State and contiguous territory as affected by growth and changes in population and economic activity and the collection and review of data relating to all factors affecting the judicious planning of construction, improvement and maintenance of highways. Such investigations may also be conducted in cooperation with counties, municipalities, the United States, sister states, agencies of any such governments or other persons in pursuance of agreements to share the cost thereof. The Department is authorized to enter into such agreements.
605 ILCS 5/4-303