35 ILCS 115/2d
For purposes of determining qualifying trips or miles, motor vehicles that carry persons or property for hire, even just between points in Illinois, will be considered used for hire in interstate commerce if the motor vehicle transports persons whose journeys or property whose shipments originate or terminate outside Illinois. The exemption for motor vehicles used as rolling stock moving in interstate commerce may be claimed only for the following vehicles: (i) motor vehicles whose gross vehicle weight rating exceeds 16,000 pounds; and (ii) limousines, as defined in Section 1-139.1 of the Illinois Vehicle Code. Through June 30, 2017, this definition applies to all property purchased for the purpose of being attached to those motor vehicles as a part thereof. On and after July 1, 2017, this definition applies to property purchased for the purpose of being attached to limousines as a part thereof.
For purposes of determining qualifying trips or miles, trailers, semitrailers, or pole trailers that carry property for hire, even just between points in Illinois, will be considered used for hire in interstate commerce if the trailers, semitrailers, or pole trailers transport property whose shipments originate or terminate outside Illinois. This definition applies to all property purchased for the purpose of being attached to those trailers, semitrailers, or pole trailers as a part thereof. In lieu of a person providing documentation regarding the qualifying use of each individual trailer, semitrailer, or pole trailer, that person may document such qualifying use by providing documentation of the following:
The definition of "use as rolling stock moving in interstate commerce" in this subsection (d-5) applies to all property purchased on or after July 1, 2017 for the purpose of being attached to a motor vehicle or trailer as a part thereof, regardless of whether the motor vehicle or trailer was purchased before, on, or after July 1, 2017.
If an item ceases to meet requirements (1) through (3) under this subsection (d-5), then the tax is imposed on the selling price, allowing for a reasonable depreciation for the period during which the item qualified for the exemption.
For purposes of this subsection (d-5):
"Motor vehicle" excludes limousines, but otherwise means that term as defined in Section 1-146 of the Illinois Vehicle Code.
"Trailer" means (i) "trailer", as defined in Section 1-209 of the Illinois Vehicle Code, (ii) "semitrailer", as defined in Section 1-187 of the Illinois Vehicle Code, and (iii) "pole trailer", as defined in Section 1-161 of the Illinois Vehicle Code.
Notwithstanding any other provision of law to the contrary, property purchased on or after January 1, 2014 for the purpose of being attached to aircraft or watercraft as a part thereof qualifies as rolling stock moving in interstate commerce only if the aircraft or watercraft to which it will be attached qualifies as rolling stock moving in interstate commerce under the test set forth in this subsection (e), regardless of when the aircraft or watercraft was purchased. Persons who purchased aircraft or watercraft prior to January 1, 2014 shall make an election to use either the trips or mileage method and document that election in their books and records for the purpose of determining whether property purchased on or after January 1, 2014 for the purpose of being attached to aircraft or watercraft as a part thereof qualifies as rolling stock moving in interstate commerce under this subsection (e).
35 ILCS 115/2d