CDL · free practice test
Free CDL practice test: general knowledge, air brakes, combination and endorsements
As of October 26, 2026, a CLP applicant must first pass a general knowledge test for the vehicle group they plan to drive (49 CFR 383.71).
Under 49 CFR 383.135, a driver must answer at least 80 percent of the questions correctly to pass each CDL knowledge test (per ecfr.gov, checked on Oct 26, 2026).
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30 free CDL practice questions
Questions from every part of the CDL knowledge tests, in the order you would study them. Pick an answer to check it; each explanation names the manual section or regulation behind it.
- General knowledge
Question 1. What is the minimum tread depth in every major groove of a front tire?
Show answer
Front tires need at least 4/32 inch of tread in every major groove. All other tires need at least 2/32 inch.
From California Commercial Driver Handbook (California DMV) · Section 2.1: Vehicle Inspection
- General knowledge
Question 2. How far ahead should you look while driving?
Show answer
Look ahead as far as you will travel in 12 to 15 seconds. That is about one block in town and about a quarter mile on the highway.
From California Commercial Driver Handbook (California DMV) · Section 2.4: Seeing
- General knowledge
Question 3. If you must stop on the road or the shoulder, how soon must you put out your emergency warning devices?
Show answer
Warning devices must be set out within 10 minutes of stopping. Also turn on your 4-way flashers, and do not count on the taillights alone to warn others.
From California Commercial Driver Handbook (California DMV) · Section 2.5: Communicating
- General knowledge
Question 4. On a wet road, how much should you reduce your speed?
Show answer
A wet road can make your stopping distance twice as long. Slow down by about one-third, for example from 55 mph to about 35 mph.
From California Commercial Driver Handbook (California DMV) · Section 2.6: Controlling Your Speed
- General knowledge
Question 5. You drive a 40-foot vehicle at 35 mph. How many seconds of following distance should you keep?
Show answer
Below 40 mph, keep at least 1 second for every 10 feet of vehicle length. A 40-foot vehicle needs 4 seconds.
From California Commercial Driver Handbook (California DMV) · Section 2.7: Managing Space
- General knowledge
Question 6. At night, you should dim your high beams when an oncoming vehicle is within how many feet?
Show answer
Dim your lights within 500 feet of an oncoming vehicle. Also dim them when you follow another vehicle within 500 feet.
From California Commercial Driver Handbook (California DMV) · Section 2.11: Driving at Night
- General knowledge
Question 7. Your safe speed for a downgrade is 40 mph and you are in the right low gear. Using the proper braking technique, you brake when you reach 40 mph. When should you release the brakes?
Show answer
Wait until you reach your safe speed, then brake just hard enough to feel a definite slowdown. Release when you are about 5 mph below the safe speed (about 3 seconds of braking), and repeat as needed.
From California Commercial Driver Handbook (California DMV) · Section 2.16.4: Proper Braking Technique
- General knowledge
Question 8. How does an anti-lock braking system (ABS) help you during hard braking?
Show answer
ABS keeps the wheels from locking up during hard braking, which helps you keep control and steer. It does not necessarily shorten your stopping distance and does not add braking power.
- General knowledge
Question 9. After you start a trip, when should you first re-check your cargo and its securing devices?
Show answer
Inspect the cargo and its securing devices again within the first 50 miles of a trip, and make any adjustments needed.
From California Commercial Driver Handbook (California DMV) · Section 3.1: Inspecting Cargo
- General knowledge
Question 10. What score do you need to pass a CDL knowledge test?
Show answer
You must answer at least 80 percent of the questions correctly to pass each CDL knowledge test.
From 49 CFR 383.135, Passing knowledge and skills tests (eCFR) · § 383.135(a)(1)
- General knowledge
Question 11. Under federal rules, you may not use alcohol within how many hours before going on duty or driving a CMV?
Show answer
You may not use alcohol, or be under its influence, within 4 hours before going on duty or driving a CMV. Using alcohol while on duty is also banned.
From 49 CFR 392.5, Alcohol prohibition (eCFR) · § 392.5(a)(1)
- General knowledge
Question 12. A property-carrying CMV driver has just had 10 consecutive hours off duty. How many hours may the driver drive, in total, before taking another 10 hours off?
Show answer
After 10 consecutive hours off duty, a property-carrying driver may drive a total of 11 hours during the work shift.
From 49 CFR 395.3, Maximum driving time for property-carrying vehicles (eCFR) · § 395.3(a)(3)(i)
- Air brakes
Question 13. At about what air tank pressure does the governor stop the compressor from pumping (the cut-out level)?
Show answer
The governor turns off the compressor's pumping once tank pressure reaches its cut-out point, which is around 125 psi.
From California Commercial Driver Handbook (California DMV) · Section 5.1: Parts of an Air Brake System
- Air brakes
Question 14. A low air pressure warning signal you can see must come on when tank pressure falls into what range?
Show answer
Every air brake vehicle needs a low-air warning, usually a red light, sometimes with a buzzer. It must come on when tank pressure falls between 55 and 75 psi (or half the governor cut-out pressure on older vehicles).
From California Commercial Driver Handbook (California DMV) · Section 5.1: Parts of an Air Brake System
- Air brakes
Question 15. What is a dual air brake system?
Show answer
A dual system has two separate air brake systems, each with its own tanks, hoses, and lines, but they share one set of brake controls. Most heavy-duty vehicles use dual systems for safety.
From California Commercial Driver Handbook (California DMV) · Section 5.2: Dual Air Brake
- Air brakes
Question 16. When you pull hard on an S-cam slack adjuster during your walk-around, how much movement means it probably needs adjustment?
Show answer
With the vehicle on level ground, wheels chocked, and parking brakes off, pull each slack adjuster you can reach. Movement of more than about one inch at the push rod connection means it probably needs adjusting.
From California Commercial Driver Handbook (California DMV) · Section 5.3: Inspecting Air Brake Systems
- Air brakes
Question 17. How do you do stab braking in an emergency stop?
Show answer
Stab braking means applying the brakes fully, letting up when the wheels lock, and reapplying fully as soon as the wheels roll again. It helps keep the vehicle in a straight line.
From California Commercial Driver Handbook (California DMV) · Section 5.4: Using Air Brakes
- Air brakes
Question 18. With air brakes, about how long does it take for the air to reach the brakes after you push the pedal (brake lag)?
Show answer
Brake lag is the delay between pushing the pedal and the brakes working. Hydraulic brakes work instantly, but with air brakes the air needs 1/2 second or more to travel through the lines.
From California Commercial Driver Handbook (California DMV) · Section 5.4: Using Air Brakes
- Combination vehicles
Question 19. Which two things help you prevent a rollover?
Show answer
Low cargo keeps the center of gravity down, and slow turns keep the rig from tipping. Keeping the load centered also helps.
From California Commercial Driver Handbook (California DMV) · Section 6.1.1: Rollover Risks
- Combination vehicles
Question 20. Trailer air lines are often color-coded. Which colors are commonly used?
Show answer
Blue marks the service line and red marks the emergency (supply) line. Some lines also have metal tags stamped "service" and "emergency."
From California Commercial Driver Handbook (California DMV) · Section 6.2.5: Hose Couplers (Glad Hands)
- Combination vehicles
Question 21. Trailers built on or after what date are required to have anti-lock brakes (ABS)?
Show answer
ABS is required on trailers built on or after March 1, 1998. Many older trailers were also equipped with ABS on a voluntary basis.
- Combination vehicles
Question 22. After the kingpin locks into the fifth wheel, how do you check that the trailer is locked onto the tractor?
Show answer
This gentle tug test shows whether the fifth wheel is holding the kingpin. Do it before the visual check of the coupling.
- Combination vehicles
Question 23. How do you test the trailer emergency brakes?
Show answer
First charge the system and make sure the trailer rolls freely. Then stop, pull the control (or set it to "emergency"), and tug gently to feel the brakes hold.
- Doubles and triples (T)
Question 24. When you pull doubles or triples, which trailer is most likely to turn over?
Show answer
Because of the crack-the-whip effect, the last trailer in the combination is the one most likely to turn over. Steer gently.
- Hazardous materials (H)
Question 25. A vehicle must be placarded. How many placards does it need, and where do they go?
Show answer
A placarded vehicle needs at least 4 matching placards: one on the front, one on the rear, and one on each side. They must be readable from all 4 directions.
From California Commercial Driver Handbook (California DMV) · Section 9.3.3: Lists of Regulated Products
- Hazardous materials (H)
Question 26. No one may smoke or carry a lit cigarette, cigar, or pipe on or within how many feet of a vehicle carrying Class 1 explosives?
Show answer
No one may smoke or carry a lit cigarette, cigar, or pipe on or within 25 feet of a vehicle carrying Class 1, Class 5, or flammable materials such as Class 3.
- Tank vehicles (N)
Question 27. Under federal rules, which setup makes a commercial vehicle a tank vehicle?
Show answer
A tank vehicle carries liquid or gas in one or more tanks, each rated at more than 119 gallons, with a total rated capacity of 1,000 gallons or more. The tanks may be permanently or temporarily attached.
From California Commercial Driver Handbook (California DMV) · Section 8: Tank Vehicles (introduction)
- Passenger (P)
Question 28. Where may standing riders be on a bus?
Show answer
No rider may stand forward of the rear of the driver's seat. Buses that allow standing have a standee line on the floor, and standing riders must stay behind it.
From California Commercial Driver Handbook (California DMV) · Section 4.2.3: Standee Line
- Passenger (P)
Question 29. On a transit bus, what does the brake-door interlock do when the rear door is open?
Show answer
With the rear door open, the interlock applies the brakes and holds the throttle at idle. It releases when the door closes, and you must not use it in place of the parking brake.
From California Commercial Driver Handbook (California DMV) · Section 4.6: Use of Brake-Door Interlocks
- School bus (S)
Question 30. How far ahead of the front bumper can a school bus danger zone extend?
Show answer
The danger zone may reach 30 feet ahead of the front bumper, and the first 12 feet are the most dangerous. It also extends 12 feet from each side and 12 feet behind the rear bumper.
From California Commercial Driver Handbook (California DMV) · Section 10.1.1: Danger Zones
What the CDL knowledge tests cover
Most drivers take general knowledge, plus air brakes for a vehicle with air brakes and combination vehicles for Class A. Each endorsement adds its own test.
| Test | Free on this page | In the full pack |
|---|---|---|
| General knowledge | 12 | 118 |
| Air brakes | 6 | 56 |
| Combination vehicles | 5 | 45 |
| Hazardous materials (H) | 2 | 32 |
| Tank vehicles (N) | 1 | 16 |
| Doubles and triples (T) | 1 | 16 |
| Passenger (P) | 2 | 16 |
| School bus (S) | 1 | 16 |
Practice every CDL test
The questions above are a sample. The pack is the whole bank, practiced one test part at a time.
Minimum ages, the 14-day wait with a learner’s permit, entry-level training and which tests each class and endorsement needs.
Learner’s permit fees, how long the permit lasts, where to test and the link to each state’s CDL manual.
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CDL practice pack
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- All 315 questions, not just these 30
- Practice one part at a time: general knowledge, air brakes, combination or an endorsement
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- Missed questions come back until you know them, for a year
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CDL practice test FAQ
What score do you need to pass the CDL permit test?
Under 49 CFR 383.135, a driver must answer at least 80 percent of the questions correctly to pass each CDL knowledge test. The free test on this page uses the same 80 percent mark for its score. Source: official page "49 CFR 383.135, Passing knowledge and skills tests (eCFR)", checked on Oct 26, 2026.
How many questions are on the CDL general knowledge test?
Each state sets the number, and many do not publish it. Among the states OneTryPass has checked, Illinois (30), Michigan (50), New Jersey (50) and Washington (50) publish it. Each state page links to the official source.
Are these the real CDL test questions?
No. OneTryPass writes its own questions from the official CDL manual and federal regulations, and each answer names the manual section or regulation it comes from. States do not publish their live test questions, and their tests change version when you retake them.
Do I need a different CDL practice test for my state?
No. Every state builds its CDL knowledge tests for each vehicle group and endorsement from the same FMCSA pre-approved pool of test questions (49 CFR 383.133). Fees, test locations and how long the learner’s permit lasts do change by state: see your state’s page. Source: official page "49 CFR 383.133, Test methods (eCFR)", checked on Oct 26, 2026.
Where this information comes from
OneTryPass writes each question from the official California Commercial Driver Handbook and from Title 49 of the Code of Federal Regulations, leaving out rules that apply only in California. A question shows here only while the rule behind it is within a year of its last check.
- California Commercial Driver Handbook (California DMV)dmv.ca.gov · checked Oct 26, 2026
- 49 CFR 383.135, Passing knowledge and skills tests (eCFR)ecfr.gov · checked Oct 26, 2026
- 49 CFR 392.5, Alcohol prohibition (eCFR)ecfr.gov · checked Oct 26, 2026
- 49 CFR 395.3, Maximum driving time for property-carrying vehicles (eCFR)ecfr.gov · checked Oct 26, 2026
- 49 CFR 397.13, Smoking (eCFR)ecfr.gov · checked Oct 26, 2026
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