CDL Practice Test: General Knowledge, HazMat & More
Every commercial driving career starts the same way: a knowledge test. Before you can get behind the wheel of a truck or bus, you need a commercial learner’s permit (CLP) — and that means passing the CDL general knowledge exam, plus a separate knowledge test for each endorsement you want. Here’s how the system fits together and how to prepare for it.
CDL classes at a glance
| Class | What it covers | Typical vehicles |
|---|---|---|
| Class A | Combination vehicles 26,001+ lb with a towed unit over 10,000 lb | Tractor-trailers, tankers, flatbeds |
| Class B | Single vehicles 26,001+ lb (towed unit under 10,000 lb) | Straight trucks, large buses, dump trucks |
| Class C | Smaller vehicles that carry 16+ passengers or placarded hazardous materials | Shuttle buses, small HazMat vehicles |
The general knowledge test
Every CDL applicant takes the general knowledge exam — in most states 50 questions with 80% (40 correct) required to pass. It covers vehicle inspection, basic control, shifting, space management, speed management, night driving, weather, mountain driving, and emergencies. Like the regular permit test, questions come straight from the state CDL manual, and the passing bar leaves little room for guessing.
Endorsement tests: HazMat and beyond
Each endorsement adds a separate knowledge test on top of general knowledge:
- HazMat (H) — hazardous materials rules, placarding, loading, and emergencies. Also requires a TSA background check and fingerprinting.
- Tanker (N) — liquid surge, baffled vs. unbaffled tanks, and rollover prevention.
- Doubles/Triples (T) — pulling multiple trailers (Class A only).
- Passenger (P) and School Bus (S) — carrying people safely; the school bus test adds loading zones, railroad crossings, and evacuation.
- Air brakes — technically a restriction-removal test, not an endorsement: fail it (or skip it) and your CDL is restricted to vehicles without air brakes.
How to study for CDL knowledge tests
- Read the state CDL manual section for each test you’ll take. General knowledge first; endorsement chapters only for endorsements you need.
- Practice by test, not all at once. Take general-knowledge practice exams until you consistently clear 80%+, then move to endorsement quizzes one at a time.
- Learn numbers cold. CDL tests love exact figures — air pressure ranges, following distance per 10 feet of vehicle length, placard thresholds. These are guaranteed questions.
- Use mistake review. Wrong answers cluster around inspection details and air brake specifics; re-drill your misses until they stop repeating. The same first-try method that works for the permit test works here.
CDL practice built into the same free app
DMV Practice Test Permit 2026 includes CDL practice tests — general knowledge, HazMat, and more — alongside car and motorcycle prep, with explanations for every answer and progress tracking per test. Free, no ads, no subscription.