49 CFR § 385.5 - Safety fitness standard.
The satisfactory safety rating is based on the degree of compliance with the safety fitness standard for motor carriers. For intrastate motor carriers subject to the hazardous materials safety permit requirements of subpart E of this part, the motor carrier must meet the equivalent State requirements. To meet the safety fitness standard, the motor carrier must demonstrate it has adequate safety management controls in place, which function effectively to ensure acceptable compliance with applicable safety requirements to reduce the risk associated with:
(h) Inadequate inspection, repair, and maintenance of vehicles (part 396 of this chapter),
(i) Transportation of hazardous materials, driving and parking rule violations (part 397 of this chapter),