The General Knowledge and Air Brakes knowledge exams together form the foundation of every standard Class A CDL. Most candidates take them on the same day — which means how you study them matters.
General Knowledge — the foundation
Every CDL applicant in every state takes the General Knowledge written exam, regardless of class or endorsement. It covers vehicle inspection, basic vehicle control, shifting, communicating in traffic, fatigue, hazardous driving conditions, accident response, weight definitions, and the broad concepts every commercial driver must know. The exam typically has 50 questions and a passing score of 80% (40/50).
Air Brakes — required for most modern trucks
Air Brakes is technically a "removed restriction" rather than an added endorsement: if you take and pass your skills test in a vehicle without air brakes (or fail the air brakes knowledge test), an "L-restriction" is printed on your license, and you're prohibited from operating air-brake-equipped commercial vehicles. Because nearly every modern Class A and Class B truck has air brakes, virtually all CDL candidates take the Air Brakes exam. It covers the dual air-brake system, brake failure indicators, parking brake operation, and the specific pre-trip air system check.
Why study them together
Roughly 30% of General Knowledge questions touch on stopping distance, braking concepts, and emergency procedures that appear again in greater technical depth on the Air Brakes exam. Studying them together produces better retention than studying them in isolation. Most CDL schools cover both in the same week of classroom instruction.
Test-day order
If your DMV office allows, take General Knowledge first, then Air Brakes — the General Knowledge framework primes you for the Air Brakes terminology. Drill our General Knowledge study guide and Air Brakes study guide before testing.