Free Alabama DMV CDL — Air Brakes Practice Test 2026
The Alabama CDL — Air Brakes knowledge test has ~25 questions, and you need ~20 correct (80%) to pass. Practice free with questions written from the official Alabama 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 Alabama written test
The Alabama CDL — Air Brakes knowledge test has ~25 questions; you need ~20 correct (80%) to pass.
Based on the official Alabama 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 Alabama practice questions.
Following distance, scanning, blind spots, using your lights, and the habits that prevent crashes and keep you in control.
Legal and illegal parking, colored curbs, distances from hydrants and crossings, and how to park safely on hills.
What to do when things go wrong — brake failure, tire blowouts, skids, and stalling on railroad tracks.
How to pass the first time
- Read the official Alabama 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.
Alabama CDL — Air Brakes test — frequently asked questions
How many questions are on the Alabama CDL — Air Brakes test?
The Alabama 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 Alabama 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 Alabama 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 Alabama 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 Alabama 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 Alabama driver handbook, practice by topic to target weak areas, and finish with full-length tests until you consistently pass.
Other Alabama practice tests
Take the CDL — Air Brakes test in another state
Every Alabama question is written from the official Alabama 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
Alabama CDL — Air Brakes questions with answers
20 sample questions from the Alabama 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. Your brakes have gotten soaked. How does the manual suggest you dry them out?
Correct answer: Roll along in a low gear and apply light brake pressure to warm them
Light braking while you roll along in a low gear builds enough friction heat to drive the water off, which matters because soaked brakes can freeze solid in cold weather.
Source: Alabama Commercial Driver License Manual, Section 5 (Air Brakes) - 5.4.8 Parking Brakes
2. In an s-cam drum brake, what happens when air enters the brake chamber?
Correct answer: The push rod moves the slack adjuster and the s-cam forces the shoes against the drum
Air pressure pushes the rod out, which moves the slack adjuster and twists the camshaft; the s-cam then turns and forces the brake shoes apart against the inside of the drum.
Source: Alabama Commercial Driver License Manual, Section 5 (Air Brakes) - 5.1.8 Foundation Brakes
3. In which situation does the manual allow a driver to push the brake pedal all the way down for an emergency stop?
Correct answer: When the truck or combination has antilock braking working on all of its axles
Full-force braking normally risks locking the wheels and losing steering. The one exception is a straight truck or combination whose antilock system is working on every axle.
Source: Alabama Commercial Driver License Manual, Section 5 (Air Brakes) - 5.4.2 Braking with Antilock Brakes
4. On a dual air system, the low air warning should come on before pressure drops below 55 psi in which system?
Correct answer: Either system
The warning light and buzzer should activate before pressure falls under 55 psi in either the primary or the secondary system, and if that happens while driving you should stop and park safely.
Source: Alabama Commercial Driver License Manual, Section 5 (Air Brakes) - 5.2 Dual Air Brake Systems
5. Bringing a truck with a manual gearbox to a routine stop, when should the clutch pedal go down?
Correct answer: Not until engine speed has dropped down near idle
Holding off until the revs fall close to idle keeps the stop smooth and keeps the engine from stalling; after you are stopped, pick a gear you can pull away in.
Source: Alabama Commercial Driver License Manual, Section 5 (Air Brakes) - 5.4.1 Normal Stops
6. If the air compressor has its own separate oil supply, what should the driver do before a trip?
Correct answer: Check the level of that oil supply
A compressor that carries its own oil, rather than sharing the engine's oil, needs its oil level checked before driving so it stays properly lubricated.
Source: Alabama Commercial Driver License Manual, Section 5 (Air Brakes) - 5.1.1 Air Compressor
7. You are pulling a trailer fitted with ABS behind a tractor that has none, and the tractor starts to jackknife. What does the manual advise?
Correct answer: Ease off the brake pedal, where it is safe, until control returns
Backing off the pedal lets the wheels roll again so steering comes back. Only ease off when traffic and the space ahead make releasing brake pressure a safe thing to do.
Source: Alabama Commercial Driver License Manual, Section 5 (Air Brakes) - 5.4.2 Braking with Antilock Brakes
8. Before driving a vehicle with a dual air system, how much pressure should you let build up in both the primary and secondary systems?
Correct answer: A minimum of 100 psi in both systems
You should allow the compressor time to build a minimum of 100 psi in both the primary and secondary systems before you drive.
Source: Alabama Commercial Driver License Manual, Section 5 (Air Brakes) - 5.2 Dual Air Brake Systems
9. In the service brake check you creep ahead at roughly five mph and press the pedal firmly. What are you looking for?
Correct answer: The truck tugging to one side, an odd feel, or a late stop
This slow-speed check exposes faults such as uneven braking, a strange pedal feel, or a stop that comes late, while you are still in the yard rather than out in traffic.
Source: Alabama Commercial Driver License Manual, Section 5 (Air Brakes) - 5.3.3 Final Air Brake Check
10. During ordinary driving, which system engages and releases the brakes as you work the pedal?
Correct answer: The service brake system
The service brake system is the one at work in everyday driving; it puts the brakes on and lets them off as you press and ease off the foot pedal.
Source: Alabama Commercial Driver License Manual, Section 5 (Air Brakes) - overview
11. If the low air pressure warning comes on while driving, why is it safer to stop while air still remains in the tanks?
Correct answer: You can still use the foot brakes for a controlled stop while air lasts
Controlled braking is only possible while enough air is left in the tanks; if you wait, the spring brakes may come on suddenly, and a heavily loaded vehicle takes a long distance to stop because they do not work on all axles.
Source: Alabama Commercial Driver License Manual, Section 5 (Air Brakes) - 5.4.7 Low Air Pressure
12. For a vehicle with air brakes, total stopping distance is made up of which four parts?
Correct answer: Perception, reaction, brake lag, and braking distance
Because of brake lag, total stopping distance for air brakes adds four parts together: perception distance, reaction distance, brake lag distance, and braking distance.
Source: Alabama Commercial Driver License Manual, Section 5 (Air Brakes) - 5.4.4 Stopping Distance
13. On newer vehicles, how do you apply the parking (spring) brakes?
Correct answer: Pull out the yellow, diamond-shaped control knob
Newer air brake vehicles use a yellow, diamond-shaped push-pull knob; you pull the knob out to set the parking brakes and push it in to release them.
Source: Alabama Commercial Driver License Manual, Section 5 (Air Brakes) - 5.1.15 Parking Brake Controls
14. Which type of foundation brake is the most common on vehicles with air brakes?
Correct answer: The s-cam drum brake
Although wedge and disc designs exist, the s-cam drum brake is the most widely used foundation brake found at the wheels.
Source: Alabama Commercial Driver License Manual, Section 5 (Air Brakes) - 5.1.8 Foundation Brakes
15. When the low air pressure warning first comes on, what is the safest thing to do?
Correct answer: Bring the vehicle to a safe stop right away
You should bring the vehicle to a safe stop right away while you still have enough air to control the brakes, rather than waiting for the spring brakes to apply on their own.
Source: Alabama Commercial Driver License Manual, Section 5 (Air Brakes) - 5.1.14 Spring Brakes
16. If one half of a dual air system loses most of its pressure, what should you expect?
Correct answer: It will take longer to stop the vehicle
With one system very low, either the front or the rear brakes will not be fully operating, so it will take you longer to stop; bring the vehicle to a safe stop and have it repaired.
Source: Alabama Commercial Driver License Manual, Section 5 (Air Brakes) - 5.2 Dual Air Brake Systems
17. How is the parking brake checked as part of the final air brake test?
Correct answer: Set it with the vehicle stopped and tug against it gently in a low gear
Setting the parking brake and then easing against it in a low gear shows whether it can really hold the vehicle before you take it out on the road.
Source: Alabama Commercial Driver License Manual, Section 5 (Air Brakes) - 5.3.3 Final Air Brake Check
18. Why can the brakes still be used several times even if the compressor quits working?
Correct answer: The tanks hold a reserve of compressed air
The storage tanks keep a reserve of compressed air, so there is enough on hand to apply the brakes a number of times even after the compressor stops.
Source: Alabama Commercial Driver License Manual, Section 5 (Air Brakes) - 5.1.3 Air Storage Tanks
19. When using the 'controlled braking' method in an emergency, how hard should you press the brakes?
Correct answer: As hard as you can without locking the wheels
Controlled braking means applying the brakes as hard as you can without locking the wheels while keeping steering movements small; if the wheels lock or you must steer more, release and then reapply.
Source: Alabama Commercial Driver License Manual, Section 5 (Air Brakes) - 5.4.3 Emergency Stops
20. What best describes a dual air brake system?
Correct answer: Two separate air systems sharing one set of controls
A dual air brake system is two separate air brake systems that share a single set of brake controls, with each system having its own tanks, hoses, and lines.
Source: Alabama Commercial Driver License Manual, Section 5 (Air Brakes) - 5.2 Dual Air Brake Systems