Code of Federal Regulations Title 49. Transportation § 49.397.203 Standards for determining preemption

(1) Compliance with both the highway routing designation and any requirement under the Act or of a regulation issued under the Act is not possible;

(2) The highway routing designation as applied or enforced creates an obstacle to the accomplishment and execution of the Act or the regulations issued under the Act;  or

(3) The highway routing designation is preempted pursuant to § 397.69(b) of this part.