Ill. Admin. Code tit. 92, § 530.700
d) Utility facilities attached to highway structures constitute varying degrees of hazards to the highway user and to the structure itself. Utility facilities transmitting commodities that are volatile, flammable, corrosive, or energized, especially those under significant pressure or potential, present the higher degrees of risk and such installations will normally not be permitted. Approval or disapproval of an application for utility attachment to a highway structure will be based on the following considerations: