Free Virginia DMV CDL — Air Brakes Practice Test 2026
The Virginia CDL — Air Brakes knowledge test has ~25 questions, and you need ~20 correct (80%) to pass. Practice free with questions written from the official Virginia driver handbook — every one has a clear explanation, and you can retake as often as you like with no sign-up.
Content reviewed against official driver handbooks · August 12, 2026
What's on the Virginia written test
The Virginia CDL — Air Brakes knowledge test has ~25 questions; you need ~20 correct (80%) to pass.
Based on the official Virginia exam format — always confirm current details with your state DMV.
Practice by topic
Focus on one area at a time — each topic has its own set of Virginia practice questions.
How to pass the first time
- Read the official Virginia driver handbook at least once before test day.
- Practice by topic to find your weak spots, then fix them.
- Take full-length practice tests until you pass comfortably every time.
- Read every explanation — understanding beats memorizing.
Virginia CDL — Air Brakes test — frequently asked questions
How many questions are on the Virginia CDL — Air Brakes test?
The Virginia CDL — Air Brakes knowledge test has ~25 questions, and you need ~20 correct (80%) to pass. Our practice tests mirror that format.
How many questions can I miss on the Virginia CDL — Air Brakes test?
You can miss up to ~5 of the ~25 questions and still pass — you need ~20 correct, which is 80%.
Can I retake the practice test?
Yes — practice as often as you like, completely free. The questions and answer choices are shuffled each time.
Can I take the Virginia practice test in Spanish?
Yes. Every question here is available in English and Spanish — switch languages anytime. Many states also offer the real knowledge test in languages other than English; confirm what Virginia offers with your DMV.
Can I practice on my phone?
Yes. The practice tests work in any mobile or desktop browser — no app or sign-up needed — so you can study anywhere.
Are these the real DMV test questions?
No. Our questions are original, written from the current official Virginia driver handbook to match the real test's topics and style. We are not affiliated with any DMV or government agency.
What's the best way to study?
Read the Virginia driver handbook, practice by topic to target weak areas, and finish with full-length tests until you consistently pass.
Other Virginia practice tests
Take the CDL — Air Brakes test in another state
Every Virginia question is written from the official Virginia driver handbook and checked against its current edition. DMV Test Free is a free, independent study resource — not affiliated with any DMV or government agency. About DMV Test Free
Virginia CDL — Air Brakes questions with answers
20 sample questions from the Virginia CDL — Air Brakes question bank — each with the correct answer, a short explanation, and the section of the official handbook it comes from.
Show all 20 questions with answers
1. A manually operated air-tank drain valve should be opened how often?
Correct answer: At the end of every day of driving
Manual drains, opened by a quarter turn or a cable pull, have to be emptied by the driver at the close of each driving day.
Source: Virginia Commercial Driver's License Manual, Section 5 (Air Brakes), 5.1.4 Air Tank Drains
2. At roughly what tank pressure does the governor 'cut out' and stop the compressor from pumping more air?
Correct answer: About 125 psi
Cut-out is the point where the governor halts the compressor because the tanks are full, and that happens at about 125 psi.
Source: Virginia Commercial Driver's License Manual, Section 5 (Air Brakes), 5.1.2 Air Compressor Governor
3. Some buses have dual parking control valves with a separate air tank. What is that separate tank for?
Correct answer: To release the spring brakes a few times so the vehicle can be moved in an emergency
The extra reservoir stores air that can release the spring brakes so the vehicle can be driven a short distance in an emergency, but it holds only enough to do this a few times, so plan the move carefully.
Source: Virginia Commercial Driver's License Manual, Section 5 (Air Brakes), 5.1.15 Parking Brake Controls
4. Compared with hydraulic brakes, why do air brakes add extra stopping distance called brake lag?
Correct answer: Air takes about a half second or more to reach the brakes
Hydraulic brakes act almost instantly, but air needs about a half second or more to travel through the lines to the brakes, which adds roughly 32 feet at 55 mph on dry pavement.
Source: Virginia Commercial Driver's License Manual, Section 5 (Air Brakes), 5.4.4 Stopping Distance
5. Why should you avoid pressing the brake pedal while the spring brakes are already applied?
Correct answer: It could damage the brakes from the combined spring and air forces
Doing so adds air-pressure force on top of the spring force, and that combined load can damage the brakes, so it is best never to make a habit of it.
Source: Virginia Commercial Driver's License Manual, Section 5 (Air Brakes), 5.1.15 Parking Brake Controls
6. How is the air compressor normally driven?
Correct answer: Off the engine, by way of gears or a v-belt
The compressor takes its power from the engine, linked to it either through gears or a v-belt, and it may be cooled and lubricated on its own or by the engine's systems.
Source: Virginia Commercial Driver's License Manual, Section 5 (Air Brakes), 5.1.1 Air Compressor
7. What is the role of the emergency brake portion of an air-brake system?
Correct answer: To stop the vehicle by using parts of the service and parking brakes when a failure occurs
The emergency brakes borrow components from the service and parking circuits so the vehicle can still be brought to a halt if the braking system fails.
Source: Virginia Commercial Driver's License Manual, Section 5 (Air Brakes) - overview
8. What are the four elements that make up total stopping distance for an air-brake vehicle?
Correct answer: Perception, reaction, brake lag, and braking distances
Air-brake vehicles add brake lag to the usual factors, so total stopping distance is perception distance plus reaction distance plus brake lag distance plus braking distance.
Source: Virginia Commercial Driver's License Manual, Section 5 (Air Brakes), 5.4.4 Stopping Distance
9. When should you NOT set the parking brakes?
Correct answer: When the brakes are very hot, or very wet in freezing temperatures
Avoid the parking brakes when the brakes are very hot from a steep grade or very wet in freezing temperatures; instead use wheel chocks, let hot brakes cool, or dry wet ones by driving lightly in low gear.
Source: Virginia Commercial Driver's License Manual, Section 5 (Air Brakes), 5.4.8 Parking Brakes
10. Which foundation-brake design is the most common on air-brake vehicles?
Correct answer: The s-cam drum brake
Although wedge and disc types exist, the s-cam drum brake is by far the most widely used foundation brake.
Source: Virginia Commercial Driver's License Manual, Section 5 (Air Brakes), 5.1.8 Foundation Brakes
11. If the safety relief valve lets air escape, what does that indicate?
Correct answer: Something is wrong and the problem should be repaired by a mechanic
The safety valve only vents when pressure climbs too high, so if it releases air something is wrong and a mechanic should correct the fault.
Source: Virginia Commercial Driver's License Manual, Section 5 (Air Brakes), 5.1.6 Safety Valve
12. You should never leave a commercial vehicle unattended without doing what?
Correct answer: Setting the parking brakes or placing chocks under the wheels
Always set the parking brakes or chock the wheels before leaving the vehicle; otherwise it could roll away and cause injury or damage.
Source: Virginia Commercial Driver's License Manual, Section 5 (Air Brakes), 5.4.8 Parking Brakes
13. What defines a dual air brake system?
Correct answer: Two separate air systems operated by one set of controls
A dual air brake system is two independent air brake systems that share a single set of brake controls, each with its own tanks, hoses, and lines.
Source: Virginia Commercial Driver's License Manual, Section 5 (Air Brakes), 5.2 Dual Air Brake
14. How does the controlled braking method work in an emergency stop?
Correct answer: Brake as firmly as you can short of locking the wheels, keeping steering inputs small
With controlled braking you apply the brakes as hard as possible without locking the wheels while keeping steering inputs small; if you must steer more or the wheels lock, you ease off and reapply.
Source: Virginia Commercial Driver's License Manual, Section 5 (Air Brakes), 5.4.3 Emergency Stops
15. On newer air-brake vehicles, what does the parking-brake control usually look like and how is it used?
Correct answer: A yellow, diamond-shaped knob you pull out to apply and push in to release
The modern parking-brake control is a yellow, diamond-shaped push-pull knob; you pull it out to set the parking (spring) brakes and push it in to release them.
Source: Virginia Commercial Driver's License Manual, Section 5 (Air Brakes), 5.1.15 Parking Brake Controls
16. What is the most common brake problem found during roadside inspections?
Correct answer: Brakes that are out of adjustment
Brakes that are out of adjustment are the single most common defect turned up in roadside inspections, which is why checking slack adjusters matters.
Source: Virginia Commercial Driver's License Manual, Section 5 (Air Brakes), 5.3.2 Walk-around Inspection
17. Which sequence correctly describes the stab braking method for an emergency stop?
Correct answer: Apply fully, release when the wheels lock, then reapply fully once they roll again
In stab braking you press the brakes all the way, release them when the wheels lock, and reapply fully once the wheels begin rolling again, remembering it can take up to a second for them to start rolling.
Source: Virginia Commercial Driver's License Manual, Section 5 (Air Brakes), 5.4.3 Emergency Stops
18. How do you test that the parking brake will actually hold?
Correct answer: Set it and, in a low gear, ease the vehicle forward against it to confirm it holds
With the vehicle stopped, set the parking brake and gently try to pull forward against it in a low gear to confirm it holds the vehicle.
Source: Virginia Commercial Driver's License Manual, Section 5 (Air Brakes), 5.3.3 Final Air Brake Check
19. Using the recommended downgrade technique with a 'safe' speed of 40 mph, at what point do you apply the brakes and to what speed do you slow before releasing?
Correct answer: Apply at 40 mph and slow to about 35 mph
You wait until you reach the safe speed of 40 mph, then brake firmly enough to drop to about 35 mph (roughly five mph below safe speed) before releasing, and repeat as needed.
Source: Virginia Commercial Driver's License Manual, Section 5 (Air Brakes), 5.4.6 Proper Braking Technique
20. The moment the low-pressure warning light and buzzer come on while you are driving, what should you do?
Correct answer: Bring the vehicle to a safe stop while you can still control the brakes
Don't wait for the spring brakes to set themselves; get the vehicle stopped safely without delay while you still have enough air to work the service brakes.
Source: Virginia Commercial Driver's License Manual, Section 5 (Air Brakes), 5.1.14 Spring Brakes