Free CDL Practice Tests — General Knowledge, Air Brakes & Endorsements

Getting your commercial driver’s license is a long road — permit, training, medical exam, knowledge tests, skills test — and the knowledge tests are where most candidates first realize how much material there is. This page collects the free CDL practice tools we offer: a quick 10-question diagnostic, study guides on every section, and a path to the full practice test course when you’re ready.

The CDL knowledge tests are computer-administered, multiple-choice, and pass at 80% (most states). General Knowledge is the test every CDL applicant takes — 50 questions covering vehicle inspection, basic control, shifting, braking, cargo, and emergencies. Air Brakes adds another 25 questions if your vehicle has air brakes (almost all Class A vehicles do). Endorsements like HazMat, Tanker, and Passenger each have their own test.

Take the free CDL diagnostic quiz →

A 10-question diagnostic covers air brakes, hours of service, pre-trip inspection, and hazmat fundamentals. Free, no signup, and you’ll see where you need to focus.

What’s on the CDL knowledge tests

The General Knowledge test covers nine major areas:

  • Vehicle inspection — pre-trip, en-route, and post-trip
  • Basic vehicle control — backing, turning, parking
  • Shifting gears — manual transmissions, downshifting on grades
  • Seeing, communicating, and managing space — mirrors, signals, following distance
  • Controlling speed — braking, stopping distance, hills, curves
  • Driver fatigue and managing health — hours of service, alertness
  • Hazardous conditions — weather, slippery surfaces, mountain driving
  • Emergencies — emergency braking, evasive steering, blowouts, fires
  • Accident procedures — what to do, what to document

Air Brakes adds: how air brakes work, slack adjusters, air-pressure tests, brake lag, and the seven-step air-brake check examiners watch for. Endorsements vary — our endorsements guide covers H (HazMat), N (Tanker), T (Doubles/Triples), P (Passenger), and S (School Bus).

Common mistakes that cost CDL applicants

  • Skipping the CDL manual. Every state DMV publishes a CDL manual that’s the authoritative source for the knowledge tests. The book is dry — but the test questions are written directly from it. Read it once cover to cover before you start practicing.
  • Memorizing answers without understanding mechanisms. Air-brake questions in particular reward people who understand how the brake system actually works (slack adjusters, S-cams, spring brakes). Memorizing “the answer is 90 psi” without context falls apart when the question is worded differently.
  • Underestimating the pre-trip on the skills test. The skills-test pre-trip is mostly about your call-outs — naming each part you inspect and what defect you’re looking for. Silent pointing fails. Practice out loud, in the order an examiner expects.
  • Treating endorsements as optional study. If you’ll be pulling a tanker or carrying HazMat, that endorsement test is a real exam with real fail rates. Plan study time for endorsements as carefully as you do for General Knowledge.
  • Booking the skills test before you’re ready. Skills-test slots are limited and re-takes cost time and money. Most candidates need 8–12 weeks of training before they’re solid on the skills test.

How to use this page

  1. Take the diagnostic to find your weak sections. The 10-question quiz covers air brakes, hours of service, pre-trip inspection, and hazmat — the four areas the General Knowledge test weights heaviest.
  2. Read the relevant study guides below for any topic where you scored under 80%. Each guide is concise and focused on the exam-tested material, not the full driver-training curriculum.
  3. Re-take the diagnostic after a week of study. Track your improvement by topic.
  4. Move to the full practice course ($12.99 one-time) when you’re scoring 80%+ on the diagnostic consistently. The full course has four 25-question sets covering all General Knowledge topics, with answer explanations.

Related study guides

Ready for the full practice tests?

The CDL Practice Tests course — $12.99 one-time, unlimited retakes — covers all four 25-question sets with answer explanations on every question. It’s the same format and difficulty as the General Knowledge and Air Brakes tests at the DMV.

Get the full CDL practice tests — $12.99

Educational purposes only. Exam Practice Hub is not affiliated with the FMCSA, NYS DMV, or any commercial driver licensing authority.