Ill. Admin. Code tit. 92 § 510.20
It will be the responsibility of the District Engineer to evaluate the hazard that might result to the highway users from objects being thrown or dropped from overhead crossings. This evaluation should include (for existing overhead crossings) all reported instances available from police or other qualified local agency records. If, in the judgement of the District Engineer, sufficient justification exists for furnishing protective fencing on existing or proposed construction, he will advise the local agency of his recommendation and if it concurs with the cost apportionment cited herein, he will submit his recommendation along with supporting documentation to the Bureau of Bridges and Structures for incorporation into construction plans.
Ill. Admin. Code tit. 92, § 510.20