Final answer:
Mud flap regulations for trucks or trailers vary by location, usually requiring that they hang within 6 to 8 inches of the highway surface to prevent road debris. Local laws must be referenced for exact requirements.
Step-by-step explanation:
The question is not directly related to the reference information provided. Mud flap regulations typically specify that mud flaps on trucks or trailers must be of a certain length. The regulations vary by location but generally require that mud flaps must reach to within a certain distance of the surface of the highway to prevent debris from being thrown up by the tires. This distance can often be around 6 to 8 inches (15 to 20 cm) from the road surface, but it is important to consult local regulations for the precise requirement.