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. Take a FREE Practice Test Now This questions appears in the following tests: Colorado HazMat , New Jersey HazMat , South Carolina HazMat ,