Section 397.203 - Standards for determining preemption(a) Any highway routing designation established, maintained, or enforced by a State, political subdivision thereof, or Indian tribe is preempted if- (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.57 FR 44132, Sept. 24, 1992, as amended at 59 FR 51834, Oct. 12, 1994