Ill. Admin. Code tit. 92 § 1535.606
On all overhead railroad structures having vertical clearance of less than 14'6" clearance, signs are to be furnished, installed, maintained and replaced by and at the expense of the public authority having the duty of maintaining the signs along the highway requiring such signs or as covered by agreement. Said signs are to be mounted on the sides of the overhead structure, one facing traffic approaching from each direction, indicating in large legible figures the appropriate numbers for clearance accommodated under the structure. It shall be the duty of said public authority to determine the clearance to be indicated on said sign. Railroad companies may elect to do the actual work of installing, maintaining or replacing clearance signs. The railroad company shall notify as soon as possible the public authority having such duties of any changes in their grade separation structures affecting such clearances.
Ill. Admin. Code tit. 92, § 1535.606