The CDL air brake restriction, and how to avoid it

What the restriction is

Under 49 CFR 383.95, a driver who does not pass the air brake knowledge test, or who takes the skills test in a vehicle without air brakes, is restricted from driving a commercial vehicle with air brakes. The restriction is printed on the license.

Why it matters more than it sounds

Most heavy trucks, tractor-trailers and many buses use air brakes. A license with the restriction rules you out of driving most of them, and an employer will see it at a glance. Removing it later means going back to sit the test you skipped.

Two ways to get it

• Through the knowledge test. Not taking Air Brakes, or not passing it at 80%, brings the restriction.
• Through the skills test. Even with the knowledge test passed, taking the road test in a vehicle without air brakes brings it too.

What the Air Brakes test covers

The parts of the system and what each does, how to check it before a trip, and how to use the brakes safely, including on a long downgrade where overusing them causes them to fade. Questions often describe a gauge reading or a warning and ask what it means and what to do.

Where people slip

The low-pressure warning and the spring brakes are the common trouble spots: what pressure brings on each, and in what order. Learn the sequence of a leakage test as a sequence, because questions often ask what you check first or what a result means.

The simple advice

Unless you are certain you will never drive a vehicle with air brakes, sit the test. It is far easier to pass now, alongside General Knowledge, than to come back for it.