What must always accompany hazardous materials during transportation?

The correct answer, proper shipping papers, is essential for the transportation of hazardous materials because they provide critical information about the contents being transported. These documents outline the specifics of the hazardous materials, including their classification, handling instructions, and emergency response information, ensuring that all parties involved in the transportation process understand the risks associated with the materials and how to handle them safely.

Proper shipping papers serve as a legal requirement, facilitating communication between shippers, carriers, and receiving facilities to ensure compliance with federal and state regulations. They are necessary for informing emergency responders in case of an incident, thereby enhancing safety during transport.

Other options, while they may provide beneficial information or protection, do not fulfill the fundamental legal requirement of containing specific information about hazardous materials during transportation. A Bill of Lading primarily serves as a contract for the carriage of goods, cargo insurance policies pertain to financial coverage and risk management rather than safety protocols, and a safety instructions booklet, while useful, does not substitute the comprehensive documentation required by law during the transport of hazardous materials.