A driver must take the HazMat knowledge test: Question A driver must take the HazMat knowledge test: Answers Once every year. Prior to every CDL renewal. Once every 10 years. Only once. Explanation You must take and pass the written English version of the HazMat knowledge test and be cleared through a federal background check before every renewal of your CDL. This questions appears in the following tests: Alabama Tank Colorado HazMat District Of Columbia HazMat Montana HazMat New Hampshire HazMat New Jersey HazMat North Dakota HazMat South Carolina HazMat