CDL Written Test: Study Guide and Practice Questions

Quick Answer

The CDL written test consists of 50 multiple-choice questions with a 60-minute time limit, requiring 80% (40 correct) to pass
Key test sections include general knowledge, air brakes, and combination vehicles (for Class A), plus additional tests for each endorsement
Most common failure topics are air brake systems, cargo securement, and hours-of-service regulations
Free practice tests are widely available at driving-tests.org, state DMV websites, and CDL study apps — aim to score 90%+ on practice before testing

The CDL written test is the first real hurdle on your path to a Commercial Driver's License. It is a knowledge test — not a driving test — and it determines whether you can obtain your Commercial Learner's Permit (CLP). Without passing the written test, you cannot begin behind-the-wheel training or take the CDL skills test.

The good news: with proper preparation, the CDL written test is highly passable. This guide covers every section of the test, the topics you need to master, study strategies that work, and practice resources to get you ready.

CDL Written Test Structure

The CDL written test is not one single test — it is a series of knowledge tests based on your CDL class and desired endorsements.

Required Tests for Class A CDL

Test	Questions	Passing Score	Time
General Knowledge	50	80% (40 correct)	60 minutes
Air Brakes	25	80% (20 correct)	30 minutes
Combination Vehicles	20	80% (16 correct)	30 minutes

Required Tests for Class B CDL

Test	Questions	Passing Score	Time
General Knowledge	50	80% (40 correct)	60 minutes
Air Brakes	25	80% (20 correct)	30 minutes

Optional Endorsement Tests

Endorsement	Code	Questions	Passing Score
Hazardous Materials	H	30	80%
Tanker	N	20	80%
Doubles/Triples	T	20	80%
Passenger	P	20	80%
School Bus	S	20	80%

All tests are multiple-choice with four answer options. The format is standardized nationally, though exact question wording may vary slightly by state.

General Knowledge Test: What to Study

The General Knowledge test covers the broadest range of topics. Here is what you need to know for each section:

Vehicle Inspection (10-15% of Questions)

Pre-trip inspection procedures and components
What to check during en-route inspections
How to report vehicle defects
When a vehicle should be taken out of service

This topic connects directly to the CDL skills test, where you will perform a pre-trip inspection for the examiner. Study this section thoroughly. For detailed inspection preparation, see our CDL pre-trip inspection guide.

Basic Vehicle Control (10-15% of Questions)

Steering techniques and hand positioning
Speed management on different road types
Space management (following distance, lane positioning)
Proper mirror use and blind spot awareness
Backing safely (straight line, offset, alley dock)

Safe Driving Practices (15-20% of Questions)

Defensive driving techniques
Handling aggressive drivers
Distracted driving hazards
Drunk driving laws and penalties
Night driving procedures
Mountain driving (grades, braking)
Winter driving (ice, snow, reduced visibility)

Cargo Handling (10-15% of Questions)

Cargo securement regulations
Weight distribution and balance
Tiedown requirements (number, type, placement)
Hazardous materials basic awareness
Sealed and bonded cargo procedures

Emergency Procedures (10-15% of Questions)

Brake failure response
Tire blowout procedures
Skid recovery techniques
Fire suppression
Emergency stopping
Accident scene procedures and reporting

Federal Regulations (15-20% of Questions)

Hours of Service (HOS) rules and limits
ELD (Electronic Logging Device) requirements
Drug and alcohol testing regulations
CDL disqualification offenses
Medical certification requirements
Interstate vs. intrastate driving rules

General Transportation Knowledge (10-15% of Questions)

Road signs and signals
Railroad crossing procedures
Bridge and tunnel restrictions
Speed limits for commercial vehicles
Right-of-way rules

Air Brakes Test: What to Study

The Air Brakes test focuses specifically on air brake systems, which are used in most commercial vehicles. Key topics:

Air Brake System Components

Compressor, governor, air storage tanks
Brake chambers and slack adjusters
S-cam brakes and wedge brakes
Spring brakes (parking/emergency)
Air lines and fittings

Air Brake Operation

Normal air pressure range (100-125 psi)
Low air pressure warning (below 60 psi)
Air brake lag (delay between application and braking)
Brake fade from overheating
Proper braking technique on grades

Air Brake Tests and Inspections

Applied pressure test
Low pressure warning signal test
Air pressure buildup rate
Air leakage rate test (acceptable limits)
Parking brake test
Service brake test

Study tip: Air brakes is the most commonly failed section of the CDL written test. Memorize the specific pressure readings (cut-in, cut-out, warning activation) and the acceptable leakage rates. These are frequently tested questions.

Combination Vehicles Test: What to Study

Required for Class A CDL only, this test covers towing and coupling:

Coupling and Uncoupling

Step-by-step coupling procedure
Step-by-step uncoupling procedure
Fifth wheel inspection and locking mechanism
Kingpin and apron inspection
Safety chain requirements

Combination Vehicle Handling

Trailer swing and off-tracking
Jackknife prevention and recovery
Rollover risks (high center of gravity, curves)
Proper lane changes with a trailer
Backing with a trailer

Air Brake Systems for Combinations

Tractor-trailer air line connections (service and emergency)
Trailer air supply valve
Emergency stopping with trailer air loss
Glad hands and dummy couplers

Study Strategies That Work

1. Start With Your State CDL Manual

Every state publishes a CDL manual (also called a handbook) that covers all test topics. This is the primary source material for the written test. Download it free from your state's DMV website or from driving-tests.org.

Read the manual cover to cover at least once. Then focus review on the sections where you feel weakest. Most manuals are 100-200 pages — plan 8-15 hours for thorough reading.

2. Take Practice Tests Repeatedly

Practice tests are the single most effective study tool. They expose you to the question format and identify knowledge gaps. Available resources:

driving-tests.org: Free CDL practice tests for all sections and endorsements
CDLStudy.com: Practice questions with detailed explanations
freedmvpracticetests.com: State-specific practice tests
CDL Prep App: Mobile practice tests for studying on the go

Target score: Aim to consistently score 90%+ on practice tests before scheduling your actual test. The passing score is 80%, but a 10% buffer accounts for exam-day stress and unfamiliar question wordings.

3. Focus on Your Weak Areas

After taking several practice tests, you will see patterns in which topics you miss. Spend extra time on these areas:

If you keep missing Air Brakes questions, re-read the manual section and memorize the pressure numbers
If cargo securement trips you up, find visual guides or videos showing tiedown methods
If Hours of Service confuses you, create a simple chart of the rules

4. Use Flashcards for Key Numbers

Many CDL test questions ask for specific numbers. Create flashcards for:

Air brake cut-in pressure (approximately 100 psi)
Air brake cut-out pressure (approximately 125 psi)
Low air pressure warning (60 psi)
Air leakage rate limits
Following distance rules
HOS driving limits (11 hours driving, 14 hours on duty)
Required tiedown numbers based on cargo length

5. Study in Short Sessions

Research on learning retention shows that multiple short study sessions are more effective than cramming. Study for 30-45 minutes at a time, 2-3 sessions per day, over 1-2 weeks. This gives your brain time to consolidate information between sessions.

Test Day Tips

Before the Test

Get a full night's sleep
Eat a meal before going to the DMV
Bring all required documents (valid license, Social Security card, proof of residency, DOT medical card)
Arrive early to avoid feeling rushed

During the Test

Read each question completely before looking at answer choices
Eliminate obviously wrong answers first
If unsure, go with your first instinct
Mark difficult questions and return to them if time permits
Do not rush — 60 minutes for 50 questions is plenty of time

If You Fail

Most states allow you to retake the test after a waiting period (typically 1-7 days). Focus your re-study on the topics you missed. There is no shame in needing a second attempt — many successful CDL holders did not pass every section on the first try.

FAQ

How hard is the CDL written test?

The CDL written test is moderately difficult for most people. With 2-3 weeks of dedicated study using the state CDL manual and practice tests, most students pass on their first attempt. Air brakes is the most challenging section. Students who consistently score 90%+ on practice tests typically pass the real test without difficulty.

How many questions are on the CDL written test?

The General Knowledge test has 50 questions. Air Brakes has 25 questions. Combination Vehicles has 20 questions. Endorsement tests range from 20-30 questions. For a Class A CDL without endorsements, you will answer a total of 95 questions across three tests.

What score do I need to pass?

You need 80% on each individual test. For General Knowledge, that means 40 out of 50 correct. For Air Brakes, 20 out of 25. For Combination Vehicles, 16 out of 20. Each test is scored independently — you can pass some and fail others, and only need to retake the ones you failed.

How long should I study for the CDL written test?

Most students need 2-3 weeks of regular study (1-2 hours daily) to prepare adequately. Students with prior mechanical or driving knowledge may need less time. Students who struggle with test-taking or have no background in vehicle systems should plan for 3-4 weeks.

Can I take the CDL written test online?

No. The CDL written test must be taken in person at your state's DMV or an authorized testing site. Some states offer computerized testing at the DMV, while others use paper-and-pencil tests. ELDT theory training can be completed online, but the actual DMV knowledge test for your CLP must be done in person.