CDL Practice Test Guide: Pass Your Written Exams in 2026

CDL Test Overview

To obtain your Commercial Learner's Permit (CLP), you must pass one or more written knowledge tests at your state's DMV. The specific tests required depend on the CDL class you are pursuing and any endorsements you want to add.

For a Class A CDL, you need to pass three written tests: General Knowledge, Air Brakes, and Combination Vehicles. For a Class B CDL, you need General Knowledge and Air Brakes (if your vehicle has air brakes). Additional endorsement tests are required for Hazmat, Tanker, Doubles/Triples, Passenger, and School Bus.

General Knowledge Test

The general knowledge test is required for every CDL class. It covers the fundamentals of safely operating a commercial motor vehicle. Expect 50 multiple-choice questions on topics including:

• Vehicle inspection: How to perform a proper pre-trip inspection, identifying defects, and understanding when a vehicle is safe to operate.
• Basic control: Steering, backing, space management, speed management, and night driving techniques.
• Shifting and transmission: Proper gear selection, progressive shifting, and double-clutching for manual transmissions.
• Cargo handling: Securing cargo, weight distribution, covering loads, and understanding cargo-related regulations.
• Hazard perception: Identifying and responding to road hazards, managing emergencies, and accident procedures.
• Hours of Service (HOS): Federal HOS rules including the 11-hour driving limit, 14-hour on-duty window, and 10-hour off-duty requirement.
• Vehicle systems: Engine, cooling system, electrical system, braking systems, and coupling devices.

The general knowledge test is the foundation for everything else. Study this material first, as it overlaps with many endorsement test topics.

Air Brakes Test

If your commercial vehicle uses air brakes (and most do), you must pass the air brakes knowledge test. Failing this test or choosing not to take it results in an air brake restriction on your CDL, which severely limits your job options. The test covers:

• Air brake system components: Compressor, governor, air tanks, brake chambers, slack adjusters, and brake drums.
• Dual air brake systems: Primary and secondary systems, spring brakes, and how they interact.
• Inspecting air brakes: What to check during pre-trip, including air pressure build-up rate, governor cut-in and cut-out pressures, and air leakage rate.
• Using air brakes: Proper braking technique, brake lag, fading, and the danger of overusing brakes on downgrades.
• Emergency and parking brakes: When spring brakes activate, proper parking procedures, and what to do during an air pressure loss.

Key numbers to memorize: the governor cut-out pressure (typically 120-145 psi), cut-in pressure (around 100 psi), minimum operating pressure (60 psi), and the low air pressure warning activation point (below 60 psi). The air pressure build-up rate should reach 85 to 100 psi within 45 seconds.

Combination Vehicles Test

This test is required only for Class A CDL applicants who will drive tractor-trailer combinations. It has about 20 questions covering:

• Coupling and uncoupling: The correct step-by-step procedure for connecting and disconnecting a tractor from a trailer, including fifth wheel inspection.
• Rollover prevention: Understanding how load height, speed on curves, and steering input affect rollover risk in combination vehicles.
• Jackknifing: What causes a tractor-trailer to jackknife, how to prevent it, and what to do if it begins to happen.
• Trailer skids: Causes of trailer skids, the difference between drive-wheel and trailer-wheel skids, and recovery techniques.
• Combination vehicle air brakes: Trailer air supply, trailer hand valve, tractor protection valve, and emergency air line operation.

The coupling and uncoupling procedure is heavily tested. Practice the steps until you can recite them from memory: inspect fifth wheel, back under trailer, lock jaws, connect air lines, connect electrical, raise landing gear, and do a tug test.

Endorsement Tests

Beyond the core tests, you can add endorsements to your CDL to qualify for specialized freight. Each endorsement requires passing an additional written test at the DMV:

• Hazmat (H): 30 questions on hazardous materials identification, placarding, loading, and emergency response. Also requires a TSA background check. This is the most valuable endorsement for pay.
• Tanker (N): 20 questions on liquid surge, rollover risks, and safe tanker operation. Combined with Hazmat gives you the X endorsement.
• Doubles/Triples (T): 20 questions on pulling multiple trailers, coupling procedures, and stability. Only available with Class A.
• Passenger (P): 20 questions on passenger safety, loading, emergency exits, and special driving considerations.
• School Bus (S): 20 questions on student loading zones, railroad crossings, and school bus-specific procedures. Requires P endorsement first.

Adding endorsements when you first get your CDL is smart because the material is fresh. The Hazmat endorsement alone can add $5,000 to $15,000 per year to your earnings.

What to Study

Your primary study resource should be your state's official CDL manual. Every state publishes one for free, either as a downloadable PDF or an online document from the DMV website. The manual covers all the material on every CDL written test.

Focus your study time on these high-priority areas:

• Numbers and thresholds: Specific values like stopping distances, air pressure levels, speed limits, weight limits, and HOS time limits. These are the most commonly tested and easiest to get wrong.
• Procedures: Step-by-step processes such as pre-trip inspection sequence, coupling/uncoupling, and emergency procedures. Know the correct order.
• Definitions: Understand terms like GVWR, GCWR, BAC limits, and the difference between gross weight and axle weight.
• Safety rules: Right-of-way, following distance (one second per 10 feet of vehicle length under 40 mph), railroad crossing rules, and mountain driving techniques.

Free Study Resources

You do not need to spend money on CDL test prep. There are excellent free resources available:

• State CDL Manual: Available free from your state's DMV website. This is the single most important study resource. Read it cover to cover at least once.
• FMCSA resources: The Federal Motor Carrier Safety Administration website has official regulations and educational materials.
• Practice test websites: Sites like Cristcdl.com and CDL Prep offer free practice tests with questions similar to the actual exam. Take multiple practice tests to identify weak areas.
• YouTube: Channels dedicated to CDL test prep offer video walkthroughs of key concepts, especially helpful for visual learners studying air brakes and vehicle systems.
• CDL study apps: Free mobile apps let you study with flashcards and practice questions during downtime.

For a structured approach to your studies, check out our 14-Day CDL Permit Study Plan, which walks you through exactly what to study each day.

Test-Taking Tips

• Read every question carefully. CDL test questions often include qualifiers like "always," "never," "except," or "most important." These words change the meaning of the question entirely.
• Eliminate wrong answers. If you are unsure, rule out the answers you know are incorrect first. On most CDL questions, at least one or two options are clearly wrong.
• Take practice tests until you consistently score 90 percent or higher. The passing score is 80 percent, but aiming for 90 gives you a comfortable margin for nerves on test day.
• Study the areas you get wrong. After each practice test, go back to the manual and re-read the sections covering your missed questions.
• Do not overthink it. The CDL test rewards knowledge of the manual, not trick reasoning. If you studied the material, the correct answer is usually straightforward.
• Get a good night's sleep before test day. Fatigue impairs your ability to recall facts. Show up rested and confident.
• Bring required documents. Your state will specify what ID and paperwork you need. Typically this includes your current driver's license, DOT medical certificate, proof of residency, and your Social Security card.

Once you pass the written tests and receive your CLP, the next step is enrolling in ELDT-registered training. Learn the full process in our How to Get a CDL guide.

Frequently Asked Questions