When are hazardous materials placards required on a vehicle?

HAZMAT PLACARDS are required when transporting certain hazardous materials at or above THRESHOLD QUANTITIES (some materials require placards in ANY amount — Table 1 materials; others only above 1,001 lbs aggregate — Table 2). CDL hazmat endorsement. Placards are diamond-shaped signs on ALL FOUR SIDES of the vehicle that identify the HAZARD CLASS by color, symbol, and number — warning the public and informing emergency responders what they're dealing with in an accident/spill. The shipper provides placarding info; the driver ensures correct placarding. Knowing when placards are required (threshold quantities; some materials always) is core hazmat knowledge.