Louisiana CDL — Air Brakes Practice Test
The Louisiana CDL — Air Brakes knowledge test has 25 questions, and you need 20 correct (80%) to pass. Practice free with questions written from the official Louisiana 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 · July 7, 2026
What's on the Louisiana written test
The Louisiana CDL — Air Brakes knowledge test has 25 questions; you need 20 correct (80%) to pass.
Based on the official Louisiana 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 Louisiana practice questions.
How to read traffic signals, lane lines, and pavement markings — including yellow and white lines, arrows, and flashing lights.
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.
Choosing a safe speed, keeping a space cushion, adjusting for weather and traffic, and understanding stopping distance.
What to do when things go wrong — brake failure, tire blowouts, skids, and stalling on railroad tracks.
The point system, license suspension, provisional-license rules, insurance requirements, and other licensing basics.
How to pass the first time
- Read the official Louisiana 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.
Louisiana CDL — Air Brakes test — frequently asked questions
How many questions are on the Louisiana CDL — Air Brakes test?
The Louisiana 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 Louisiana 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 Louisiana 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 Louisiana 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 Louisiana 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 Louisiana driver handbook, practice by topic to target weak areas, and finish with full-length tests until you consistently pass.
Other Louisiana practice tests
Take the CDL — Air Brakes test in another state
Every Louisiana question is written from the official Louisiana 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
Louisiana CDL — Air Brakes questions with answers
20 sample questions from the Louisiana CDL — Air Brakes question bank — each with the correct answer, a short explanation, and the section of the official handbook it comes from.
1. Air brakes are actually made up of which three separate braking systems?
Correct answer: The service, parking, and emergency braking systems
An air brake setup combines three systems: the service brakes for everyday driving, the parking brakes, and the emergency brakes that stop the rig if something fails.
Source: Louisiana Commercial Driver's License Manual, Section 5 - Air Brakes
2. What must you always do before leaving your vehicle unattended?
Correct answer: Apply the parking brakes or chock the wheels
An unattended vehicle can roll away, so always set the parking brakes or chock the wheels before walking away.
Source: Louisiana Commercial Driver's License Manual, Section 5.4.8 - Parking Brakes
3. What does the stop light switch do in an air brake system?
Correct answer: It turns on the brake lights to warn drivers behind you
An air-operated electric switch turns on the brake lights so following drivers know you are braking.
Source: Louisiana Commercial Driver's License Manual, Section 5.1.12 - Stop Light Switch
4. In a dual air system, if one of the two systems gets very low on pressure, what happens?
Correct answer: Either the front or rear brakes will not fully work, so it takes longer to stop
When one circuit loses pressure, only part of the braking remains, so stopping takes longer; stop safely and get it repaired.
Source: Louisiana Commercial Driver's License Manual, Section 5.2 - Dual Air Brake
5. Why does a heavily loaded vehicle need a long distance to stop once the spring brakes come on?
Correct answer: The spring brakes do not act on all of the axles
Because the spring brakes do not work on every axle, a heavy load takes a long distance to stop; it is far safer to stop while there is still enough air for the foot brakes.
Source: Louisiana Commercial Driver's License Manual, Section 5.4.7 - Low Air Pressure
6. When checking manual slack adjusters, about how much movement means they probably need adjustment?
Correct answer: More than roughly one inch of play at the push-rod connection
If a slack adjuster shifts more than roughly one inch at the push-rod connection, it likely needs adjusting; out-of-adjustment brakes are the most common roadside-inspection defect.
Source: Louisiana Commercial Driver's License Manual, Section 5.3.2 - Walk-around Inspection
7. Why should you avoid pressing and releasing the brake pedal more than necessary?
Correct answer: It can release air faster than the compressor can replace it, dropping pressure until the brakes fail
Each release lets air out; fanning the pedal drains the tanks faster than the compressor refills them, and low pressure means no braking.
Source: Louisiana Commercial Driver's License Manual, Section 5.1.7 - The Brake Pedal
8. On newer air-brake vehicles, how do you apply the parking brakes?
Correct answer: Pull out the diamond-shaped yellow push-pull knob
Newer vehicles use a yellow, diamond-shaped push-pull control; pull it out to set the parking or spring brakes and push it in to release them.
Source: Louisiana Commercial Driver's License Manual, Section 5.1.15 - Parking Brake Controls
9. A visible low air pressure warning must come on before tank pressure falls below what level?
Correct answer: 60 psi
The warning signal you can see is required to activate before the air pressure drops under 60 psi.
Source: Louisiana Commercial Driver's License Manual, Section 5.1.11 - Low Air Pressure Warning
10. What is 'brake lag' in an air brake system?
Correct answer: The short delay for air to reach the brakes after you press the pedal
Unlike instant hydraulic brakes, air brakes have a lag of about a half second or more while air travels through the lines to the brakes.
Source: Louisiana Commercial Driver's License Manual, Section 5.4.4 - Stopping Distance
11. On the application pressure gauge, needing more and more pressure to hold the same speed is a sign of what?
Correct answer: The brakes are fading, so slow down and use a lower gear
If it takes rising application pressure just to maintain speed, the brakes are fading; the response is to slow down and shift to a lower gear.
Source: Louisiana Commercial Driver's License Manual, Section 5.1.10 - Application Pressure Gauge
12. What is the job of the service brake system?
Correct answer: It applies and releases the brakes when you press the pedal in normal driving
The service brakes are the ones you work with the foot pedal during ordinary driving, applying and releasing as you press and ease off.
Source: Louisiana Commercial Driver's License Manual, Section 5 - Air Brakes
13. Why should you avoid pressing the brake pedal while the spring brakes are applied?
Correct answer: The combined force of the springs and the air pressure could damage the brakes
Adding air pressure on top of the spring force can damage the brakes, so it is best never to push the pedal when the spring brakes are set.
Source: Louisiana Commercial Driver's License Manual, Section 5.1.15 - Parking Brake Controls
14. What does a supply pressure gauge tell the driver?
Correct answer: How much air pressure is in the storage tanks
The supply gauge reads the pressure held in the tanks; a dual system has one for each half, or a single gauge with two needles.
Source: Louisiana Commercial Driver's License Manual, Section 5.1.9 - Supply Pressure Gauges
15. Total stopping distance for an air-brake vehicle is made up of which factors?
Correct answer: Perception, reaction, brake lag, and braking distance
Air brakes add a brake-lag component, so total stopping distance combines perception, reaction, brake lag, and braking distances.
Source: Louisiana Commercial Driver's License Manual, Section 5.4.4 - Stopping Distance
16. What should you do when the low air pressure warning first comes on?
Correct answer: Stop the vehicle safely without delay, while you still have enough air to control it
Do not wait for the spring brakes to grab on their own; stop safely as soon as the warning appears, while you still have control of the brakes.
Source: Louisiana Commercial Driver's License Manual, Section 5.1.14 - Spring Brakes
17. Using the proper downhill braking method, when should you release the brakes?
Correct answer: After your speed drops to about 5 mph below your safe speed
Apply firmly enough to feel a definite slowdown, then release once you are about 5 mph below your safe speed, repeating as needed.
Source: Louisiana Commercial Driver's License Manual, Section 5.4.6 - Proper Braking Technique
18. When should you NOT use the parking brakes?
Correct answer: When the brakes are very hot from a steep grade, or very wet in freezing temperatures
Hot brakes can be damaged and wet brakes can freeze; in those cases use wheel chocks instead and let the brakes cool or dry first.
Source: Louisiana Commercial Driver's License Manual, Section 5.4.8 - Parking Brakes
19. Where is the yellow ABS malfunction lamp located on a trailer?
Correct answer: On the left side, at the front or rear corner
Trailers carry the yellow ABS malfunction lamp on the left side, either the front or rear corner; tractors and trucks show it on the dash.
Source: Louisiana Commercial Driver's License Manual, Section 5.1.16 - Antilock Braking Systems (ABS)
20. What does 'controlled braking' mean during an emergency stop?
Correct answer: Braking as firmly as possible just short of a wheel lockup, using only small steering inputs
Controlled braking means braking hard but short of lockup while keeping steering inputs small; if the wheels lock or you must steer more, release and re-apply.
Source: Louisiana Commercial Driver's License Manual, Section 5.4.3 - Emergency Stops