49 C.F.R. § 397.219 : Transportation — OTHER REGULATIONS RELATING TO TRANSPORTATION — FEDERAL MOTOR CARRIER SAFETY ADMINISTRATION, DEPARTMENT OF TRANSPORTATION — FEDERAL MOTOR CARRIER SAFETY REGULATIONS — TRANSPORTATION OF HAZARDOUS MATERIALS; DRIVING AND PARKING RULES — PREEMPTION PROCEDURES — Waiver determination and order

(a) Upon consideration of the application and other relevant information received or obtained during the proceeding, the Administrator issues an order setting forth his or her determination.
(b) The Administrator may issue a waiver of preemption order only if he or she finds that the requirement of the State, political subdivision thereof, or Indian tribe affords the public a level of safety at least equal to that afforded by the requirements of the Act and the regulations issued under the Act and does not unreasonably burden commerce. In determining whether the requirement of the State, political subdivision thereof, or Indian tribe unreasonably burdens commerce, the Administrator may consider the following factors:
(1) The extent to which increased costs and impairment of efficiency result from the highway routing designation of the State, political subdivision thereof, or Indian tribe;
(2) Whether the highway routing designation of the State, political subdivision thereof, or Indian tribe has a rational basis;
(3) Whether the highway routing designation of the State, political subdivision thereof, or Indian tribe achieves its stated purpose; and
(4) Whether there is need for uniformity with regard to the subject concerned and if so, whether the highway routing designation of the State, political subdivision thereof, or Indian tribe competes or conflicts with those of other States, political subdivisions thereof, or Indian tribes.
(c) The order includes a written statement setting forth the relevant facts and the legal basis for the determination, and provides that any person aggrieved by the order may file a petition for reconsideration in accordance with §397.223.
(d) The Administrator serves a copy of the order upon the applicant, any other person who participated in the proceeding and upon any other person readily identifiable by the Administrator as one who may be affected by the order. A copy of each order is placed on file in the public docket. The Administrator may publish the order or notice of the order in the Federal Register.
(e) If no petition for reconsideration is filed within 20 days in accordance with §397.223, an order issued under this section constitutes the final agency decision regarding whether a particular requirement of a State, political subdivision thereof, or Indian tribe is preempted under the Act or any regulations issued thereunder, or whether preemption is waived.

49 C.F.R. § 397.219