49 CFR 392.2
Every commercial motor vehicle must be operated in accordance with the laws, ordinances, and regulations of the jurisdiction in which it is being operated. However, if a regulation of the Federal Highway Administration imposes a higher standard of care than that law, ordinance or regulation, the Federal Highway Administration regulation must be complied with.
[35 FR 7800, May 21, 1970, as amended at 60 FR 38746, July 28, 1995].