Commercial Driver's License (CDL) Knowledge Tests Practice Test
Federal knowledge tests for Class A, Class B and Class C: General Knowledge, Air Brakes, Combination Vehicles, plus Hazmat, Tanker and Passenger endorsements.
What the CDL knowledge tests are
A Commercial Driver's License is issued by your state, to federal standards. The written tests come from the same core manual in every state: General Knowledge for every class, then extra tests for air brakes, combination vehicles and endorsements.
| Test | Who sits it | Typical size | Pass |
|---|---|---|---|
| General Knowledge | Every CDL | 50 questions | 80% |
| Air Brakes | Any air-brake vehicle | 25 | 80% |
| Combination Vehicles | Class A | 20 | 80% |
| Hazmat (H) | Placarded hazardous materials | 30 | 80% |
| Tanker (N) | Tank vehicles | 20 | 80% |
| Passenger (P) | 16+ including the driver | 20 | 80% |
You also need a Commercial Learner's Permit (CLP) before the skills test. Read CDL permit and Class A vs Class B. Passing is 80% on each test, not an average — passing score.
State pages (same federal bank, local booking): California, Texas, Florida, Georgia.
How CertReady helps
Questions are original practice material on the same topics the knowledge tests use — space and cargo, hours of service, air-brake parts, coupling, placards, surge and passenger stops. Each item has an explanation. Start with the free CDL practice test or a timed mock exam.
CertReady is not a trucking school, not a state DMV, and not FMCSA. Passing a mock here does not issue a CDL.
Who should take this exam
- Anyone sitting CDL General Knowledge for Class A, B or C
- Class A applicants who also need Air Brakes and Combination Vehicles
- Drivers adding H (hazmat), N (tanker) or P (passenger)
- CLP holders waiting out the permit period before the skills test
- Drivers transferring a CDL or refreshing after time off the road
You still take the skills test (pre-trip, basic control, road) at the state after the knowledge tests. This bank is the written part only.
Interstate driving generally requires age 21 and a valid DOT medical examiner's certificate. Intrastate Class B at 18 is a state rule, not a federal interstate CDL. School bus (S) and doubles/triples (T) are not in this bank yet.
What's on the exam
Practice each section separately or mix them in a mock exam.
General Knowledge
40% of examRequired for every CDL class: vehicle control, space, cargo, hours of service, inspections, emergencies and the Class A / B / C split.
35 practice questions →
Air Brakes
20% of examRequired if you will drive a vehicle with air brakes. Dual air systems, lag, slack adjusters, spring brakes, ABS and leak tests.
16 practice questions →
Combination Vehicles
15% of examRequired for Class A: coupling, off-tracking, jackknife, trailer swing and air-line / fifth-wheel checks.
12 practice questions →
Hazardous Materials (H)
12% of examH endorsement: shipping papers, placards, hazard classes, loading and what to do in a leak or fire.
12 practice questions →
Tanker (N)
8% of examN endorsement: liquid surge, baffles vs smoothbore, outage and high center of gravity.
10 practice questions →
Passenger (P)
5% of examP endorsement: buses designed for 16 or more including the driver — railroad stops, evacuation and passenger safety.
10 practice questions →
Practice questions
Untimed sets with instant feedback and an explanation for every answer. Choose quick, by-topic or random.
Start practiceMock exams
50 questions in 50 minutes, weighted like the real exam, with a category breakdown at the end.
Start mock examFrequently asked questions
- How many questions are on the CDL General Knowledge test?
- Most states use 50 multiple-choice questions and require 80% (40 correct). Air Brakes is typically 25, Combination Vehicles 20, and endorsements 20–30. Confirm the count with your state, because a few use slightly different banks.
- What is the CDL passing score?
- 80% on each knowledge test, scored separately. A high General Knowledge score does not save a failed Air Brakes test. Failed Air Brakes usually means an air-brake restriction on the license.
- What is the difference between Class A and Class B?
- Class A is a combination with GCWR of 26,001 lb or more and a trailer of 10,001 lb or more. Class B is a single vehicle of 26,001 lb or more (you may tow under 10,001 lb). Class A requires the Combination Vehicles test.
- Do I need a CDL permit before the road test?
- Yes. After you pass the knowledge tests the state issues a Commercial Learner's Permit. You must hold it for a waiting period (often 14 days) and practice with a qualified CDL driver before the skills test.
All questions on CertReady are original practice material. They are not actual exam questions, and CertReady is not affiliated with or endorsed by State driver-licensing agencies.