Commercial Driver License Test Prep focuses on the test truckers must take every 5 years to renew their licenses. The subjects are comprehensive & take some serious study to answer the questions properly. Additional helpful data also included. The subject matter has expanded over the years to include more environmental & safety questions. The author got a CDL to improve his pay so relates to the importance of the test and renewal study. The subject was recommended by trucker Nathan Huckaby of Orlando who suggested that audio was the best way for truckers to learn, while driving. Many truckers have agreed and none not. So thanks to our friend Nathan!