What must be visible on all four sides of a HAZMAT railcar?

The correct answer pertains to the importance of appropriate placards on all four sides of a HAZMAT railcar. Placards serve as visual indicators that communicate the type of hazardous material contained within the railcar. These placards are crucial for ensuring safety during transport and handling, as they inform emergency responders and personnel about the potential risks associated with the materials.

Visibility on all four sides allows for immediate recognition of the hazard, regardless of the railcar's orientation or the direction from which it is approached. This is particularly vital in emergencies or incidents where quick identification of materials can guide appropriate response measures to mitigate any dangers.

While company name and logo, emergency contact information, and truck identification numbers are important for identification and operational purposes, they do not directly communicate the hazardous nature of the materials being transported. Therefore, having appropriate placards is fundamental for safety and compliance with regulations governing the transport of hazardous materials.