430 ILCS 105/4

Any portion of highway or bridge which is closed to all traffic shall be marked at each place where vehicles have accessible approach to such portion of highway or bridge, and at a sufficient distance from the closed portion of such highway or bridge shall be marked with an adequate number of safe, suitable, and proper warning signs, signals or barricades as set forth in the Manual of Uniform Traffic Control Devices for Streets and Highways published by the Department of Transportation so as to give warning to approaching motorists that such portion of bridge or highway is closed and unsafe for travel.