CDL Knowledge Test guides
30 source-backed guides for the CDL, from registration and scoring to what to study, exam day and retakes.
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New to the CDL? These answer the first questions most candidates have.
- 1Study strategies
CDL Permit Test Study Guide: How to Prepare for the Knowledge Tests
A study order for the CDL knowledge tests, a map from the federal topic lists to the sections of your state's manual, and a method that still works when the questions change.
Read guide - 2Eligibility, registration & costs
Which CDL Knowledge Tests Do You Need? Tests by Class and Endorsement
A decision table that turns your license class, your vehicle's brakes and trailer, and the work you plan to do into the list of CDL knowledge tests to take.
Read guide - 3What to study
CDL General Knowledge Test: The 20 Federal Topics and How to Study Them
The 20 knowledge areas in federal law, grouped into six study blocks, with the decision each block usually tests, an original scenario for each, and the numbers worth memorizing.
Read guide - 4What to study
CDL Air Brakes Test: The Seven Federal Topics and the Numbers Behind Them
Who has to take the CDL Air Brakes knowledge test, the seven areas federal rules require, what happens if you do not pass, and the typical pressures and leakage limits to know, each with its conditions and the places where state manuals differ.
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Getting started3 guides
What the exam is, who takes it, how it compares and how hard it is.
Entry-Level Driver Training (ELDT): Who Needs It and When It Must Be Done
Who must complete entry-level driver training, where it fits between the CDL permit and the skills test, what the federal curriculum requires, and how to check a provider on FMCSA's registry.
Read guideCDL Skills Test: Pre-Trip, Basic Control, and Road Test (Current vs Modernized)
What each CDL skills test segment checks, why a failed segment ends the test, how your test vehicle sets restrictions, and how to find out which test version your state uses.
Read guideHow Hard Is the CDL Permit Test? What Trips People Up, Plus a Self-Check
Why the CDL permit test trips people up: separate tests at 80% each, air brake numbers with conditions, three close options, changing versions, and a ten-item self-check.
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Eligibility, registration & costs5 guides
Who can sit the exam, how to apply and schedule, and what it costs.
CDL Class A, B, and C: Weight Ratings and What Each License Covers
How the federal CDL groups are drawn, why weight ratings decide the class, and three worked rigs that show where Class A starts, including a pickup that crosses the line.
Read guideWhich CDL Knowledge Tests Do You Need? Tests by Class and Endorsement
A decision table that turns your license class, your vehicle's brakes and trailer, and the work you plan to do into the list of CDL knowledge tests to take.
Read guideCDL Learner's Permit (CLP) Rules: Age, Medical Card, the 14-Day Wait, and Supervision
What a commercial learner's permit allows, who must ride with you, the P, S and N limits, how long the permit lasts, and the medical self-certification behind it.
Read guideCan You Take the CDL Test in Spanish or Another Language? What Applies in 2027
What a 2027 CDL applicant can expect on test language: the federal knowledge-test rule, the English-only skills test, English proficiency as a driver qualification, and dated state examples.
Read guideHow to Get a CDL: From Permit to License, Step by Step
The steps from choosing a license class to holding a CDL, the federal clocks that run along the way, and a cost worksheet you can fill in from your state's fee page.
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Exam format & scoring1 guide
Questions, sections, timing and the score you need to pass.
What to study20 guides
The content areas, skills and topics the exam actually tests.
The Air Brake Check, Step by Step: Leakage, Low-Air Warning, and Spring Brakes
The air brake check in the order the model manual teaches it, what each step proves, the typical limits for single and combination vehicles, how the skills-test version differs, and a worked gauge example in which the same leak gets two different verdicts.
Read guideCDL Air Brake Restrictions (L and Z) and the Other Restriction Codes
What the L and Z air brake restrictions mean, how each federal CDL and CLP restriction code is triggered, how to remove L, Z, E, and O, and why some letters mean one thing as an endorsement and another as a restriction.
Read guideAir Brake System Parts: Compressor, Governor, Tanks, Spring Brakes, and Dual Systems
What each part of a truck air brake system does and what its failure looks like, how air travels from the compressor to the brake shoe, and why water, oil, and a severed line matter on the Air Brakes test.
Read guideCDL Air Brakes Test: The Seven Federal Topics and the Numbers Behind Them
Who has to take the CDL Air Brakes knowledge test, the seven areas federal rules require, what happens if you do not pass, and the typical pressures and leakage limits to know, each with its conditions and the places where state manuals differ.
Read guideCargo on the CDL General Knowledge Test: Weight, Tie-Downs, and When to Recheck
The cargo knowledge area of the CDL General Knowledge test: weight ratings and axle weights worked through on an original load, balance and center of gravity, blocking and tie-downs, and the federal schedule for rechecking a load.
Read guideCDL Combination Vehicles Test: What It Covers and Why It Gates Class A
The three federal areas behind the Combination Vehicles knowledge test, why failing it blocks a Class A permit, and the rollover, off-tracking, and trailer-brake ideas that most of its questions turn on.
Read guideCoupling and Uncoupling a Tractor-Trailer: The Order and What Each Step Prevents
The coupling and uncoupling sequence for a tractor and semitrailer, grouped by purpose, with the failure each step prevents, the tug test and fifth-wheel gap check, and the chock logic for uncoupling.
Read guideDoubles and Triples Endorsement (T): What the Test Covers and State Limits on Triples
What the CDL T endorsement test covers, why the heaviest trailer goes first, how converter dollies work, why the last trailer rolls first, and where triples are banned.
Read guideCDL Endorsements Explained: H, N, T, P, S, and X
What each CDL endorsement allows, which tests it takes, whether it needs ELDT or can go on a learner's permit, and which endorsement a given job calls for.
Read guideCDL Following Distance and Stopping Distance: The Math With Worked Examples
The seconds rule for following distance worked for three rig lengths, the parts of total stopping distance, why air brakes add lag, and why speed outweighs load.
Read guideCDL General Knowledge Test: The 20 Federal Topics and How to Study Them
The 20 knowledge areas in federal law, grouped into six study blocks, with the decision each block usually tests, an original scenario for each, and the numbers worth memorizing.
Read guideHazards, Skids, and Emergency Maneuvers on the CDL General Knowledge Test
The hazard clues, emergency steering rules, braking methods, skid recoveries, and brake and tire failure responses that the CDL General Knowledge test covers, each with an original scenario and the reason the tempting answer is wrong.
Read guideHazMat Endorsement (H): TSA Threat Assessment, ELDT Theory, and the Knowledge Test
The steps to a CDL hazardous materials endorsement in order: ELDT theory, the H knowledge test, TSA's security threat assessment and its $88.25 fee, issuance, and the five-year renewal cycle.
Read guideNight, Weather, Mountain Grades, and Rail Crossings on the CDL General Knowledge Test
How the CDL General Knowledge test treats downgrades, brake fade, escape ramps, black ice, hydroplaning, night glare, fatigue, and railroad crossings, with worked examples.
Read guidePassenger Endorsement (P): Knowledge Test, Skills Test, and ELDT
The steps to a CDL passenger endorsement in order, why P is tied to the bus class you test in, the M and N restrictions, and what the P knowledge test covers.
Read guideSchool Bus Endorsement (S): Requirements and Test Topics
What the CDL school bus endorsement requires, why it starts with the passenger endorsement, what the S knowledge and skills tests cover, and which rules your state and district set.
Read guideTank Vehicle Endorsement (N): Surge, Baffles, and the CLP Empty-Tank Rule
When a truck counts as a tank vehicle, what the N knowledge test covers, how surge and baffles change handling, and what an N endorsement on a learner's permit allows.
Read guideTrailer Air Brakes: Emergency and Service Lines, the Tractor Protection Valve, and the Supply Knob
How a tractor feeds air to trailer brakes, what happens when the red or blue line fails, when the tractor protection valve closes, how crossed lines and glad hands cause trouble, and why the trailer hand valve is not a parking brake.
Read guideVehicle Inspection on the CDL General Knowledge Test: What to Check and Why
What the General Knowledge test expects you to know about pre-trip, en route, and post-trip inspections, the defects that matter in each system, tread depth, emergency equipment, and inspection reports.
Read guideHow Long Does It Take to Study for the CDL Permit Test?
A method for budgeting CDL permit study time by the tests you still need, with example profiles, and how the permit, training, and skills-test clocks fit together.
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Study strategies1 guide
Study plans, practice tests and how to prepare in the time you have.
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