The eight knowledge-test areas
General Knowledge
Required for every CDL applicant
Safe driving basics, vehicle inspection, shifting, speed and space management, seeing hazards, night and bad-weather driving, and cargo rules. This is the foundation everything else builds on.
Air Brakes
Required to drive vehicles with air brakes
Air brake system parts, dual air systems, inspecting air brakes, and using them properly. Fail it (or skip it) and your CDL carries an air-brake restriction.
Combination Vehicles
Required for Class A
Coupling and uncoupling, pulling trailers safely, preventing rollovers and jackknifes, and inspecting combination vehicles.
Hazardous Materials (H)
Endorsement
Identifying, loading, and transporting placarded hazardous materials. Also requires a TSA security threat assessment and, under ELDT, registry training for first-time applicants.
Tanker (N)
Endorsement
Hauling liquid loads: surge, baffles, outage, and the special handling tank vehicles demand.
Doubles/Triples (T)
Endorsement
Pulling two or three trailers: coupling order, stability, and the much smaller margin for error.
Passenger (P)
Endorsement
Loading, unloading, and driving vehicles designed for 16 or more people, plus emergency procedures.
School Bus (S)
Endorsement
Student loading zones, railroad crossings, emergency exits, and the danger zones around the bus. Taken alongside the passenger endorsement.
How to study so the test feels familiar
- Study your state's CDL manual first
- Knowledge-test questions come from your state's manual, and details like question counts and fees vary by state. Practice questions are for testing yourself after you've read the material — not a substitute for it.
- Practice in small, frequent sessions
- Short daily sessions beat marathon cramming for retention. Track which modules you're weakest in and spend your time there.
- Read every answer explanation
- The goal isn't memorizing answer letters — it's understanding why an answer is right. That's what carries you through differently-worded real exam questions.
- Simulate the exam before the real one
- Do timed, full-length runs without looking anything up. If you can't pass your own honest exam simulation, you're not ready to pay for the real one.
Where to go next
Haven’t started the licensing process yet? Start a CDL Career walks the whole path. The TruxCel app turns these eight modules into practice sessions, exam simulations, and progress tracking.
