Here, you can take any additional test by itself. $10. The Hazmat test has to be retaken every time you renew and it also requires a background check each time you renew.  As far as the tanker and air brake endorsement just reading the book once should be good to pass them. For the Hazmat I always read the book the day before the test and again while in the car outside the license center. The only problem I had was that pesky vision test.