Free CDL Knowledge Tests practice test (20 questions)
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Question 1After a commercial learner's permit is first issued, how long must the holder wait before taking the CDL skills test?
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Answer: C — 14 days.
Federal rules make a CLP holder ineligible to take the CDL skills test during the first 14 days after the CLP is first issued. The wait gives time for supervised behind-the-wheel practice.
Checked against: 49 CFR 383.25(e)
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Question 2During your walk-around you measure 3/32 inch of tread in a major groove of a front (steer) tire. What does this mean?
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Answer: D — The tire is below the 4/32 inch minimum for front tires.
Front tires need at least 4/32 inch of tread in every major groove, so 3/32 inch is too little. The 2/32 inch minimum applies only to the other tires, which is why it is a tempting but wrong answer for a steer tire.
Checked against: CA Commercial Driver Handbook, 2.1.3 What to Look For, Tire Problems (NY CDL Manual 2.1.3)
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Question 3A driver keeps their eyes fixed on the vehicle directly ahead and rarely looks farther down the road. What is the main risk?
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Answer: B — They may have to stop too quickly or make quick lane changes.
Most good drivers look at least 12 to 15 seconds ahead. If you do not look that far ahead, you may have to stop too quickly or make quick lane changes; good drivers still shift attention back and forth, near and far.
Checked against: CA Commercial Driver Handbook, 2.4.1 Seeing Ahead (NY CDL Manual 2.4.1)
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Question 4When you must stop on a road or its shoulder, how soon must you put out your emergency warning devices?
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Answer: B — Within 10 minutes.
Warning devices must be placed as soon as possible and in any event within 10 minutes of stopping. Turn on the 4-way flashers right away and keep them on until the devices are placed.
Checked against: CA Commercial Driver Handbook, 2.5.2 Communicating Your Presence (NY CDL Manual 2.5.2); 49 CFR 392.22(b)(1)
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Question 5Which part of total stopping distance covers the distance traveled from the time your eyes see a hazard until your brain recognizes it?
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Answer: A — Perception distance.
Perception distance runs from seeing a hazard to recognizing it; reaction distance runs from recognizing it to physically hitting the brakes; braking distance is the distance traveled while braking. Together they make up total stopping distance.
Checked against: CA Commercial Driver Handbook, 2.6.1 Stopping Distance (NY CDL Manual 2.6.1)
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Question 6You drive a 40-foot truck at 35 mph. How much following distance should you keep?
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Answer: A — At least 4 seconds.
The rule is at least 1 second for each 10 feet of vehicle length at speeds below 40 mph. A 40-foot vehicle below 40 mph needs 4 seconds.
Checked against: CA Commercial Driver Handbook, 2.7.1 Space Ahead, Figure 2.12 (NY CDL Manual 2.7.1)
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Question 7About how far ahead can a driver see with low-beam headlights at night?
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Answer: B — About 250 feet.
With low beams you can see ahead only about 250 feet (about 350-500 feet with high beams). Your speed must let you stop within that distance, so night speeds often need to be lower than daytime speeds.
Checked against: California Commercial Driver Handbook, Section 2.11.4 Vehicle Factors - Headlights; same text in NY CDL-10 Manual 2.11.4
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Question 8According to the CDL manual, what is the best advice for driving in fog?
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Answer: B — Do not drive in it; pull off into a rest area or truck stop until visibility improves.
The best advice for fog is not to drive in it. If you must, slow down before entering it, use low beams and fog lights, and avoid passing.
Checked against: California Commercial Driver Handbook, Section 2.12 Driving in Fog; same text in NY CDL-10 Manual 2.12
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Question 9You are driving a typical tractor-trailer toward a crossing with two sets of tracks and no signals. Before you start across, how much clear time should you expect to need to get the whole rig past both tracks?
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Answer: D — More than 15 seconds.
The manual says a typical tractor-trailer needs at least 14 seconds to clear a single track and more than 15 seconds to clear a double track. Never start across unless you can get all the way over.
Checked against: California Commercial Driver Handbook, Section 2.15.5 Crossing the Tracks; same text in NY CDL-10 Manual 2.15.5
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Question 10On a long, steep downgrade, what should be your principal way of controlling speed?
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Answer: D — The braking effect of the engine in a low gear.
Engine braking should be the main way to control speed on a downgrade; the brakes are only a supplement. Save your brakes for slowing or stopping as traffic requires.
Checked against: California Commercial Driver Handbook, Section 2.16.1 Select a Safe Speed; same text in NY CDL-10 Manual 2.16.1
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Question 11Under federal rules, what alcohol concentration bars a driver from performing safety-sensitive functions such as driving a CMV?
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Answer: C — 0.04 or greater.
No driver may report for or remain on duty requiring safety-sensitive functions with an alcohol concentration of 0.04 or greater. It is a much lower limit than the one most states apply to drivers of ordinary cars.
Checked against: 49 CFR 382.201 Alcohol concentration (eCFR, current as of 2026-09-30)
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Question 12After beginning a trip, when must you first re-inspect your cargo and its securing devices?
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Answer: B — Within the first 50 miles.
Inspect the cargo and securing devices within the first 50 miles, then again as needed during the trip.
Checked against: 49 CFR 392.9(b)(2) Inspection of cargo, cargo securement devices and systems (eCFR, current as of 2026-09-30); California Handbook 3.1
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Question 13On a typical air brake system, at about what tank pressure does the governor stop the compressor from pumping air (the cut-out level)?
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Answer: A — About 125 psi.
The governor cuts the compressor out at around 125 psi and lets it cut back in when tank pressure falls to around 100 psi. 150 psi is the usual opening setting of the safety valve, not the governor cut-out.
Checked against: California Commercial Driver Handbook, Section 5 Air Brakes, 5.1.2 Air Compressor Governor; same in NY CDL-10 (11/25) 5.1.2
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Question 14On a tractor or straight truck, the spring brakes come fully on when air pressure drops into which range?
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Answer: D — 20 to 45 psi.
Tractor and straight truck spring brakes come fully on when air pressure drops to a range of 20 to 45 psi (typically 20 to 30 psi). Do not wait for this: stop safely as soon as the low air warning comes on, while you can still control the brakes.
Checked against: California Commercial Driver Handbook, Section 5 Air Brakes, 5.1.14 Spring Brakes; same in NY CDL-10 (11/25) 5.1.14
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Question 15During the static air leakage test on a single vehicle (engine off, brakes released, system fully charged), which one-minute pressure loss marks the limit?
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Answer: A — 2 psi.
California says a single vehicle should lose no more than 2 psi in one minute and New York says less than 2 psi; a two-vehicle combination is allowed 3 psi. A larger loss points to a leak that must be fixed before the vehicle is driven.
Checked against: California Commercial Driver Handbook, Section 5 Air Brakes, 5.3.3 Step 7: Final Air Brake Check, Test Air Leakage Rate (Static Leakage Test); same in NY CDL-10 (11/25) 5.3.3 Test Air Leakage Rate
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Question 16You are in the proper low gear on a long downgrade and your safe speed is 40 mph. Using the braking technique in the manual, when should you release the brakes after an application?
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Answer: B — When the speed has dropped to about 35 mph.
Brake just hard enough to feel a definite slowdown, and release when you are about 5 mph below your safe speed (40 down to 35 mph); the application should last about 3 seconds. When speed climbs back to 40 mph, repeat.
Checked against: California Commercial Driver Handbook, Section 5 Air Brakes, 5.4.6 Proper Braking Technique; same in NY CDL-10 (11/25) 5.4.6
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Question 17On many combination vehicles, which color marks the emergency (supply) air line and its glad hand?
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Answer: B — Red.
Red is used for the emergency (supply) line and blue for the service line, so the two glad hands are not mixed up. Some lines also carry metal tags stamped "service" and "emergency."
Checked against: California Commercial Driver Handbook, Section 6.2.5 Hose Couplers (Glad Hands); same text in NY CDL-10 Section 6.2.5
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Question 18What is the main job of the tractor protection valve?
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Answer: C — It keeps air in the tractor or truck brake system if the trailer breaks away or develops a bad leak.
The tractor protection valve protects the tractor's own air supply when the trailer breaks away or leaks badly. It closes automatically when pressure falls into the 20 to 45 psi range, which also sets the trailer emergency brakes.
Checked against: California Commercial Driver Handbook, Section 6.2.2 Tractor Protection Valve; same text in NY CDL-10 Section 6.2.2
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Question 19When a tractor-semitrailer goes around a corner, which wheels off-track the most?
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Answer: A — The rear wheels of the trailer.
Rear wheels follow a shorter path than front wheels. The tractor's rear wheels off-track some, and the trailer's rear wheels off-track even more, so you must steer the front end wide enough to keep them off the curb.
Checked against: California Commercial Driver Handbook, Section 6.1.6 Turn Wide; same text in NY CDL-10 Section 6.1.6
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Question 20A driver hauling a heavy load wants to lower the risk of a rollover. Which plan follows the handbook's advice?
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Answer: C — Keep the cargo as low as possible and drive slowly around turns.
A low, centered load keeps the center of gravity close to the road, and slow turning keeps the rig from tipping. Cargo piled high or pushed to one side, and fast turns or quick lane changes, all make a rollover more likely.
Checked against: California Commercial Driver Handbook, Section 6.1.1 Rollover Risks; same text in NY CDL-10 Section 6.1.1
Official passing standard: At least 80% correct on each knowledge test (49 CFR 383.135). With 50, 25 and 20 questions (Washington), that is 40, 20 and 16 correct answers.
CDL Knowledge Tests format
| Section | Questions | Time |
|---|---|---|
| General Knowledge | 50 | — |
| Air Brakes | 25 | — |
| Combination Vehicles | 20 | — |
| CDL Knowledge Tests | Official rule |
|---|---|
| Passing score | At least 80% correct on each knowledge test, scored separately; a state must give a different version of a test you retake after failing it source |
| General Knowledge test | Taken by every Class A, B and C applicant. Washington: 50 questions, 40 correct to pass. source |
| Air Brakes test | Needed to drive a vehicle with air brakes, including air-over-hydraulic brakes. Washington: 25 questions, 20 correct to pass. source |
| Combination Vehicles test | Needed for a Class A CDL. Washington: 20 questions, 16 correct to pass. source |
| Same lengths in Utah | Utah: General Knowledge 50 questions, Combination 20, Air Brakes 25; all CDL tests closed-book multiple choice, 80% to pass, English only source |
| Question format | Multiple choice: you choose one correct answer from three choices (New York CDL manual, section 1.4.1) source |
| CDL classes | Class A: combination with a GCWR of 26,001 lb or more, towing more than 10,000 lb GVWR. Class B: single vehicle of 26,001 lb or more GVWR. Class C: smaller vehicle designed for 16 or more people including the driver, or placarded hazardous materials. source |
| Commercial learner's permit (CLP) and 14-day wait | You must be 18 or older and pass the General Knowledge test for your vehicle group to get a CLP. A CLP is valid for no more than 1 year from first issue (California and Washington issue it for 180 days, renewable once), and you cannot take the CDL skills test in the first 14 days after it is first issued. source |
| Minimum age | 18 for a CLP or CDL; at least 21 to drive a commercial motor vehicle in interstate commerce. Under 21, drivers are limited to intrastate driving (for example New York and Washington) source |
| Entry-level driver training (ELDT) | Required before the skills test for a first Class A or B CDL (or a B-to-A upgrade) and before the skills test for a first P or S endorsement, from a provider on FMCSA's Training Provider Registry. Not required before the General Knowledge, Air Brakes or Combination tests; it is required before the hazardous materials (H) knowledge test. source |
| Endorsements | Knowledge test only: Doubles/Triples (T), Tank (N), Hazardous materials (H). Knowledge and skills tests: Passenger (P), School bus (S). Washington lengths: hazmat 30 questions; doubles/triples, tank, passenger and school bus 20 each. source |
| If you skip or fail Air Brakes | Your CLP or CDL is restricted from operating any commercial vehicle with air brakes (the same happens if you take the skills test in a vehicle without air brakes) source |
| DOT medical certificate | Most commercial driving needs a DOT medical exam by an examiner on FMCSA's National Registry; the certificate is normally valid up to 24 months source |
| Languages | Federal rules allow knowledge tests in a foreign language as long as no interpreter is used; the skills test is in English only. Washington offers the CDL knowledge test in English, Spanish, Russian and Serbian-Croatian; Utah gives CDL tests in English only. source |
| Fees (examples) | Set by each state. Washington: $35 CDL knowledge test, $40 CLP, $175 skills test. source |
Checked on the official sources on October 3, 2026. Rules change: always confirm on the official site before test day.
Practice by section
CDL General Knowledge practice test
15 free questions with explanations
CDL Air Brakes practice test
15 free questions with explanations
CDL Combination Vehicles practice test
15 free questions with explanations
Who takes the CDL knowledge tests
You need a commercial driver's license (CDL) to drive the heavier trucks, buses and hazmat vehicles defined in 49 CFR 383.91. The first step is a set of written knowledge tests at your state's licensing agency. Passing them gets you a commercial learner's permit (CLP), which lets you practice on public roads with a qualified CDL holder beside you.
FMCSA does not issue CDLs: your state does. Federal rules set the minimum standards, and states build their tests from an FMCSA-approved pool of questions. That is why the core content is the same everywhere, while test lengths, fees and retake rules vary from state to state.
Which tests you take
The tests depend on the class of license and the endorsements you want (classes defined in 49 CFR 383.91):
| You want to drive | Class | Knowledge tests |
|---|---|---|
| Tractor-trailer or other combination with a GCWR of 26,001 lb or more, towing more than 10,000 lb | A | General Knowledge + Combination Vehicles (+ Air Brakes if the vehicle has air brakes) |
| Single vehicle with a GVWR of 26,001 lb or more (dump truck, box truck, large bus) | B | General Knowledge (+ Air Brakes if needed) |
| Smaller vehicle carrying 16 or more people including the driver, or placarded hazmat | C | General Knowledge + the matching endorsement test |
Air Brakes matters for most truck drivers. If you skip or fail it, your permit and license carry a restriction that bars you from driving any commercial vehicle with air brakes (49 CFR 383.95). Most tractor-trailers have air brakes, so a Class A truck driver normally takes all three tests: General Knowledge, Air Brakes and Combination Vehicles. If you fail Combination Vehicles, your state cannot issue a Class A CLP or CDL.
Endorsements add their own tests (49 CFR 383.93). Doubles/Triples (T), Tank (N) and Hazardous Materials (H) need a knowledge test only. Passenger (P) and School Bus (S) need both a knowledge test and a skills test. Our practice tests cover the three core tests, not the endorsements.
Format and passing score
Federal rules require you to answer at least 80% of the questions correctly on each knowledge test (49 CFR 383.135). Each test is scored on its own, so a strong General Knowledge score does not make up for a weak Air Brakes score.
Test lengths are published by each state. Washington's CDL knowledge test page lists:
| Test | Questions | Correct answers to pass |
|---|---|---|
| General Knowledge | 50 | 40 |
| Air Brakes | 25 | 20 |
| Combination Vehicles | 20 | 16 |
Utah publishes the same 50, 25 and 20 questions, closed-book. Washington also lists 30 questions for Hazmat and 20 for each other endorsement. Other states may differ, so check your state's CDL manual or website.
The questions are multiple choice. New York's manual says you choose one correct answer from three choices. We found no federal time limit, and the state pages we checked do not state one. California tells applicants to allow 2 to 3 hours if taking all tests.
If you fail, you can try again, and the state must give you a different version of the test. Retake limits are set by each state. California allows three attempts at each required test on one application. Utah charges a $26 test fee after two attempts.
From CLP to skills test
To get a CLP you must be at least 18 and pass the General Knowledge test for the vehicle group you will drive. You also need a regular driver's license from the same state, proof of identity and residence, and a 10-year driving history check. To drive across state lines (interstate commerce) you must be at least 21. Under 21, states such as New York limit you to driving within the state.
A CLP is valid for no more than one year from first issue without retaking the knowledge tests. California and Washington issue it for 180 days, renewable once. You cannot take the skills test in the first 14 days after your CLP is first issued (49 CFR 383.25(e)). The skills test has three parts taken in order: vehicle inspection, basic vehicle control and the road test. It is given in English only.
Entry-level driver training (ELDT)
If you are getting a Class A or B CDL for the first time, or upgrading from B to A, you must complete entry-level driver training from a provider listed on FMCSA's Training Provider Registry before the skills test. The same applies before the skills test for a first Passenger or School Bus endorsement, and before the knowledge test for a first Hazmat endorsement (49 CFR 383.71(a)(10)).
You do not need ELDT before the General Knowledge, Air Brakes or Combination tests. FMCSA states there is no federal requirement to finish ELDT theory before applying for a CLP, though some states add their own rules.
The DOT medical certificate
Most commercial drivers must pass a DOT physical with an examiner on FMCSA's National Registry, and FMCSA notes that you bring proof of medical qualification when you apply for the CLP. A medical certificate is normally valid for up to 24 months; New York's manual notes the examiner may issue it for a shorter period. Book the exam early so it does not hold up your permit.
Fees
Fees are set by each state. For example, Washington charges $35 for the CDL knowledge test, $40 for the CLP and $175 for the skills test. Check your own state's fee page before you go.
How to prepare
Your state's CDL manual is free, and it is the book the questions are written from. Many states follow the same national model: the California Commercial Driver Handbook and the New York CDL Manual have the same section numbers. Study these sections:
- General Knowledge: sections 1, 2 and 3 (introduction, driving safely, transporting cargo). New York also lists the inspection and skills test sections, 11 to 13.
- Air Brakes: section 5.
- Combination Vehicles: section 6, plus section 5, because combination questions cover trailer air brakes (New York manual, section 1.4.1).
Read one section at a time and answer the review questions at the end of it. Then take an untimed practice test and reread the parts behind every miss. Air Brakes and Combination questions are very specific: glad hands, the tractor protection valve, spring brakes, the low-air warning and the coupling steps. Learn them in the order the manual gives them.
On test day
Bring the documents your state lists, including your driver's license, proof of identity and residence, and your medical certificate where required. Testing aids are not allowed: California marks a test as failed if you use notes, the handbook or a phone. Arrive well before closing time: California does not start knowledge tests within 30 minutes of closing. Read every choice before you answer. Many wrong answers are "almost right" numbers taken from a nearby rule.
Frequently asked questions
How many questions are on the CDL permit test?
It depends on your state and on how many tests you take. Washington publishes 50 questions for General Knowledge, 25 for Air Brakes and 20 for Combination Vehicles, and Utah publishes the same numbers. A Class A applicant who takes all three therefore answers 95 questions, with each test scored separately. Source
What score do I need to pass?
Federal rules require at least 80% correct on each knowledge test. On a 50-question General Knowledge test that means 40 correct; on 25 Air Brakes questions, 20; on 20 Combination questions, 16. Source
Which knowledge tests do I need for a Class A CDL?
General Knowledge and Combination Vehicles, plus Air Brakes if you will drive a truck with air brakes (most tractor-trailers have them). Without the Air Brakes test you get an air brake restriction, and failing Combination Vehicles means no Class A permit or license can be issued. Endorsements such as Doubles/Triples, Tank or Hazmat need their own tests. Source
Do I need entry-level driver training (ELDT) before the written tests?
No, not for General Knowledge, Air Brakes or Combination Vehicles. FMCSA says there is no federal requirement to finish ELDT theory before applying for a CLP. ELDT from a registered provider is required before the skills test for a first Class A or B CDL, before the skills test for a first P or S endorsement, and before the hazardous materials knowledge test. Some states add their own requirements. Source
What happens if I fail a CDL knowledge test?
You can retake it, and the state must give you a different version of the test. Retake limits are set by each state: California allows 3 attempts at each required knowledge test per application with no waiting period, New York has no fixed limit, and Utah charges a second test fee after two attempts. Source
How long is a CLP valid, and when can I take the skills test?
Federally, a CLP is valid for no more than one year from first issue without retaking the knowledge tests; California and Washington issue it for 180 days with one renewal. You must hold the CLP for at least 14 days before taking the skills test. Source
Is the CDL knowledge test timed?
Federal rules do not set a time limit, and the Washington, Utah, New York and California pages we checked do not state one for these tests. California tells applicants to allow 2 to 3 hours if they are taking all tests. Ask your own testing office. Source
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Sources
- California Commercial Driver Handbook (current edition linked by the California DMV, © 2019-2021) — California Department of Motor Vehicles (checked October 3, 2026)
- New York State Commercial Driver's Manual (CDL-10), sections 1-13 — New York State DMV (checked October 3, 2026)
- California DMV: Commercial Driver's Licenses (CLP and CDL application, attempts, 14-day wait) — California Department of Motor Vehicles (checked October 3, 2026)
- Washington DOL: CDL knowledge test (types of tests, number of questions, passing scores, languages) — Washington State Department of Licensing (checked October 3, 2026)
- Washington DOL: Commercial learner's permit (CLP) — Washington State Department of Licensing (checked October 3, 2026)
- Washington DOL: Driver licensing fees (CDL knowledge test, CLP, skills test) — Washington State Department of Licensing (checked October 3, 2026)
- Utah Driver License Division: CDL Written Knowledge Test — Utah Department of Public Safety, Driver License Division (checked October 3, 2026)
- 49 CFR Part 380: Special Training Requirements (Subpart F, entry-level driver training) — eCFR, National Archives (checked October 3, 2026)
- 49 CFR Part 382: Controlled Substances and Alcohol Use and Testing — eCFR, National Archives (checked October 3, 2026)
- 49 CFR Part 383: Commercial Driver's License Standards; Requirements and Penalties — eCFR, National Archives (checked October 3, 2026)
- 49 CFR Part 391: Qualifications of Drivers — eCFR, National Archives (checked October 3, 2026)
- 49 CFR Part 392: Driving of Commercial Motor Vehicles — eCFR, National Archives (checked October 3, 2026)
- 49 CFR Part 393: Parts and Accessories Necessary for Safe Operation — eCFR, National Archives (checked October 3, 2026)
- 49 CFR Part 395: Hours of Service of Drivers — eCFR, National Archives (checked October 3, 2026)
- FMCSA: Commercial Driver's License, Drivers (classes, endorsements, restrictions, CLP) — Federal Motor Carrier Safety Administration (checked October 3, 2026)
- FMCSA: How do I get a Commercial Driver's License? — Federal Motor Carrier Safety Administration (checked October 3, 2026)
- FMCSA: Entry-Level Driver Training (ELDT) — Federal Motor Carrier Safety Administration (checked October 3, 2026)
- FMCSA Training Provider Registry — Federal Motor Carrier Safety Administration (checked October 3, 2026)
passmock is an independent practice service. It is not affiliated with or endorsed by the Federal Motor Carrier Safety Administration (FMCSA), the U.S. Department of Transportation, the American Association of Motor Vehicle Administrators (AAMVA) or any state DMV, DPS or driver licensing agency. Our questions are original practice questions written from the official state CDL manuals and federal regulations; they are not taken from any state's test. Our questions are original practice questions written from the official test description and study materials; they are not questions from the real test.
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