Where must U.S. DOT placards be displayed on a vehicle?

The correct answer indicates that U.S. DOT placards must be displayed on all four sides of a vehicle. This requirement is essential for ensuring proper identification of hazardous materials being transported. By placing placards on all sides, emergency responders, law enforcement, and the general public can quickly recognize the nature of the materials, which is critical for safety during transportation and in case of an accident or spill.

Visibility from all angles helps in conveying important information regarding the potential hazards, allowing those nearby to take appropriate precautions. This is especially relevant in situations where prompt action may be necessary, such as during emergencies. Unlike options that suggest limiting placards to one or two sides, the placement on all four sides ensures comprehensive visibility and compliance with federal regulations governing the transport of hazardous materials.