The purpose of the CDL hazardous materials test is to ensure that truck drivers know how to safely transport potentially dangerous material. Trucks transport a wide range of material, and small mistakes can lead to disastrous outcomes.
Truck drivers are ultimately responsible for ensuring that the material they ship is transported as safely as possible, so they need to know how to interpret safety information about the products they carry. For example, some materials can't be transported safely in a refrigerated truck; drivers must be able to recognize if a shipment request is potentially dangerous. Similarly, drivers need to know where they can park safely, and testing ensures that drivers don't leave trailers in potentially dangerous areas.
Testing also ensures that truck drivers know how to interpret safety labeling. The so-called "fire diamond" is a common sight on trailers, and drivers should know how to interpret it in case they're involved in an accident. The three top corners of the diamond list how dangerous the material being transported is based on its flammability, instability and potential to pose health problems. The bottom of the label reveals other potential risks. Radioactive material, for example, is noted in this space. By knowing this information, truck drivers are better able to respond to requests by emergency personnel and keep dangerous material out of restricted areas.