65 ILCS 5/11-86-4
If the street designated in Section 11-86-3 is to be used only for boulevard purposes, it may be extended through such park at the grade of other roadways to be crossed by such street so to be extended within such park in the discretion of the park commissioners having control thereof. If such street is to be used for general traffic purposes, it shall be depressed below the street level within such park, as the park commissioners, having control thereof, shall direct. The cost of the construction and maintenance of such depression shall be borne by the city. No such street or streets shall be extended through any park in any city without the consent and express direction of the park commissioners having control of such park.
65 ILCS 5/11-86-4