The CDL Air Brakes test, and the restriction behind it

This one is not an endorsement

The other seven tests add something to a license. This one removes something from it if you do not take it. A driver who never sits Air Brakes, or sits it and fails, gets a restriction printed on the license saying they may not operate a commercial vehicle equipped with air brakes. Since most heavy vehicles have them, that restriction closes off most of the work.

Seven subjects

49 CFR 383.111(b) sets them. Air brake system nomenclature. The dangers of a contaminated air supply. Severed or disconnected air lines. What low air pressure readings imply. Safe and accurate pre-trip inspections. En route and post-trip inspections. General operating practices and procedures.

Three of the seven are inspection

Pre-trip, en route and post-trip each get their own line in the regulation. That is unusual: no other knowledge test splits inspection three ways. It tells you where the questions live. If you can walk through an air brake check out loud, in order, naming what you are listening for and what reading you expect, you have covered a large share of the test.

The failure questions

Contaminated air, severed lines, falling pressure. These are not trivia. They are the three ways an air brake system tells you it is about to stop being a brake, and the test asks what the driver does about each. Answers that involve continuing to the next stop are usually the wrong ones.

Passing it

Three choices a question and 80% to pass, the same federal numbers as every other knowledge test. Our own forms run twenty-five questions, which is our length and not New York's, since the state publishes no count for this test.