What shape must U.S. DOT placards be?

U.S. DOT placards must be in the shape of a diamond to ensure consistency and recognition across various transportation modes. The diamond shape is universally understood in the context of hazardous materials, making it easier for first responders and the public to quickly identify the potential risks associated with the materials being transported. This designation facilitates clear communication about the nature of the hazard and helps ensure that emergency protocols are followed appropriately. The use of a diamond shape is standardized so that it can be easily seen and identified, which is critical for safety in transportation and emergency situations.