What is one key factor in determining which placards to use?

The selection of placards is primarily governed by the materials hazard class, which indicates the specific dangers associated with the hazardous materials being transported. Each hazard class corresponds to a distinct set of risks, such as flammability, toxicity, or radioactivity. By following established regulations, individuals can ensure that the appropriate placards are used to clearly communicate these dangers to other road users and emergency responders. This level of awareness is crucial for maintaining safety during transportation and in case of an incident.

While other factors like vehicle type, traffic conditions, and driver experience may influence transportation logistics or safety practices, they do not directly determine the specific placards required. The materials hazard class remains the fundamental basis for placard selection, as it specifically categorizes the hazards involved.