Commercial driver's licence airbrake practice tests are available on websites such as CDLTest.co and TruckerCountry.com. The first site offers a list of practice written CDL exams for various endorsements and specializations; click on the Air Brake Practice Test to begin. The main Trucker Country page offers a CDL Practice Center link. Click it, and then click Air Brake Tests on the following page to access practice tests.
Trucker Country offers three modes of air brake practice exams, as of 2015: Classic, Practice and Exam. Each mode consists of seven parts, and the modes differ by time limit and supplemental information. The Classic and Practice modes are not timed, while the Exam mode is; the latter best simulates the pressure of taking the actual test. The Practice mode provides a correct or incorrect response for each answer as well as reference material related to the question to teach the subject more effectively. The Classic mode is a practice test that scores the answers at the end.
By contrast, CDLTest.co only scores the air brake test at the end. It grades by the percentage of correct answers to questions overall and provides statistics indicating which questions other users got right or wrong.