Ill. Admin. Code tit. 92, § 533.60 – Vehicles

a) Vehicles are restricted to surfaced areas only and operators shall obey all traffic signs and markings.
b) Rest areas shall not be used as a relay station or transfer point for trailers or cargo in transit. No cargo, trailer, or mobile home shall be uncoupled from its power unit within the rest area, except in the case of mechanical breakdown or other emergency.
c) Vehicles shall occupy no more than one marked parking space.
d) Rest areas shall not be used to change oil or to perform any other automotive service. Minor repairs will be allowed.