Vermont Air Brakes CDL Practice Test
25 realistic Air Brakes practice questions for Vermont CDL applicants. Required for: Vehicles equipped with air brake systems. Official test: 25 questions, 20 correct to pass.
Question 1 of 25 · Combination Air
What does the trailer hand valve do?
-
A.
Operates only the trailer brakes
-
B.
Operates both the tractor and trailer brakes
-
C.
Engages the parking brakes
-
D.
Lowers the landing gear
Correct answer: A.
The hand valve (trolley valve) controls only the trailer service brakes.
Question 2 of 25 · System Basics
Air brakes use compressed air to:
-
A.
Lubricate the wheels
-
B.
Make the brakes work
-
C.
Cool the engine
-
D.
Increase fuel pressure
Correct answer: B.
Compressed air is the working fluid that applies the brakes in an air brake system.
Question 3 of 25 · Speed Management
Which of these statements is true about brake fading?
-
A.
Resting brakes does not bring back braking power
-
B.
Brake fade is caused by drums getting too hot
-
C.
Brake fade only affects new vehicles
-
D.
Brake fade only happens with disc brakes
Correct answer: B.
Brake fade results from overheated drums or discs reducing friction and braking ability.
Question 4 of 25 · Speed Management
Brake fade results from:
-
A.
Oversized brakes
-
B.
Excessive heat from prolonged braking
-
C.
Too much air pressure
-
D.
Cold weather
Correct answer: B.
Brake fade is caused by overheating brakes that lose stopping power.
Question 5 of 25 · Inspection
How much air pressure (psi) loss is allowed per minute for single vehicles with the engine off and brakes released?
-
A.
Up to 1 psi
-
B.
Up to 2 psi
-
C.
Up to 3 psi
-
D.
Up to 4 psi
Correct answer: B.
Single vehicles allow up to 2 psi per minute with brakes released; up to 3 psi with brakes applied.
Question 6 of 25 · Spring Brakes
If your vehicle has dual parking control valves, you can use pressure from a separate tank to:
-
A.
Charge the trailer brakes
-
B.
Release the spring brakes to move a short distance if the main system loses air
-
C.
Operate the steering
-
D.
Power the air horn
Correct answer: B.
Dual parking control valves let you temporarily release spring brakes from a backup tank.
Question 7 of 25 · ABS
Which is true about ABS?
-
A.
It activates only on dry roads
-
B.
It activates only when wheels are about to lock during heavy braking
-
C.
It is the same as anti-skid
-
D.
It eliminates the need for skid recovery
Correct answer: B.
ABS activates only when wheels are about to lock; otherwise the brake system operates normally.
Question 8 of 25 · Compressor
What is the purpose of a one-way check valve?
-
A.
Allow air to flow in one direction
-
B.
Allow water to drain
-
C.
Prevent the trailer from moving
-
D.
Increase pressure in the supply tank
Correct answer: A.
It permits airflow in one direction only — protecting the system if the compressor fails.
Question 9 of 25 · Inspection
What is the air loss rate for combination vehicles with brakes applied?
-
A.
1 psi per minute
-
B.
2 psi per minute
-
C.
3 psi per minute
-
D.
4 psi per minute
Correct answer: D.
Combination vehicles can lose up to 4 psi per minute with brakes applied.
Question 10 of 25 · Foundation Brakes
Brake drums (or discs) must not have cracks longer than:
-
A.
1/4 the width of the friction area
-
B.
1/2 the width of the friction area
-
C.
3/4 the width of the friction area
-
D.
Anything is acceptable
Correct answer: B.
Cracks longer than one-half the width of the friction area are a safety violation.
Question 11 of 25 · Inspection
How can you check the slack adjusters?
-
A.
Pull hard on each slack adjuster — they should not move more than about 1 inch
-
B.
Listen for air leaks at each chamber
-
C.
Watch the brake light flash
-
D.
Look at the brake pedal travel
Correct answer: A.
Pulling hard, slack adjusters should not move more than about 1 inch where the push rod attaches.
Question 12 of 25 · Compressor
The air compressor governor controls:
-
A.
When the air compressor will pump air into the storage tanks
-
B.
When the brakes are applied
-
C.
When emergency brakes engage
-
D.
How fast the air compressor turns
Correct answer: A.
The governor cuts the compressor in and out to keep the system within its operating pressure range.
Question 13 of 25 · Inspection
When should you check the parking brake?
-
A.
Whenever you start a trip
-
B.
Once a month
-
C.
Only at inspections
-
D.
When the brake warning light is on
Correct answer: A.
Test the parking brake every trip — apply the brake and try to move forward gently.
Question 14 of 25 · Speed Management
Air brake lag distance at 55 mph on dry pavement adds about:
-
A.
12 feet to stopping distance
-
B.
32 feet to stopping distance
-
C.
50 feet to stopping distance
-
D.
100 feet to stopping distance
Correct answer: B.
Air brake systems have a lag of about 0.4 seconds, adding roughly 32 feet at 55 mph.
Question 15 of 25 · ABS
If the ABS warning light comes on, you should:
-
A.
Stop driving immediately
-
B.
Continue, knowing brakes still work — but ABS may not
-
C.
Pump the brakes constantly
-
D.
Engage the trailer hand valve
Correct answer: B.
You still have normal braking; only the ABS function may be off. Get it fixed soon.
Question 16 of 25 · Emergency Maneuvers
Stab braking includes which of these steps?
-
A.
Apply brakes fully, release when wheels lock, reapply when wheels begin rolling
-
B.
Apply brakes lightly until they fade
-
C.
Pump the brakes rapidly
-
D.
Apply the parking brake repeatedly
Correct answer: A.
Stab braking: full application, release on lockup, reapply when wheels turn again.
Question 17 of 25 · Compressor
Brake-system air pressure should build from 85 to 100 psi within:
-
A.
15 seconds in dual systems
-
B.
30 seconds in dual systems
-
C.
45 seconds in dual systems
-
D.
60 seconds in dual systems
Correct answer: C.
Build-up time should be within 45 seconds in dual air systems.
Question 18 of 25 · Spring Brakes
Spring brakes will come on automatically when air pressure drops to:
-
A.
100 psi
-
B.
60 psi or less
-
C.
20 to 45 psi
-
D.
10 psi
Correct answer: C.
Spring brakes typically apply automatically between 20 and 45 psi.
Question 19 of 25 · Gauges
The supply pressure gauge tells you:
-
A.
The pressure of brake fluid
-
B.
How much air pressure is in the air tanks
-
C.
The trailer brake pressure
-
D.
The temperature of the brake
Correct answer: B.
The supply gauge shows the air pressure available in the storage tanks.
Question 20 of 25 · Gauges
You should know your vehicle is properly equipped with which gauge?
-
A.
Two air pressure gauges (or one with two needles) showing pressure in primary and secondary tanks
-
B.
A vacuum gauge
-
C.
A voltage meter only
-
D.
A coolant gauge only
Correct answer: A.
Dual air systems require gauges for both primary and secondary air supplies.
Question 21 of 25 · Inspection
How do you test the low pressure warning signal?
-
A.
With the engine off, pump the brake pedal until the signal activates (must come on at 60 psi or above)
-
B.
Drive the vehicle to lose pressure
-
C.
Open the air tank drain valve briefly
-
D.
Push the parking brake control
Correct answer: A.
Pump the brake to lower pressure; warning must come on at 60 psi or higher.
Question 22 of 25 · Parking
Why should you use chocks?
-
A.
When parking on a hill
-
B.
On level ground when leaving the vehicle
-
C.
Whenever brakes might fail or it's required by company policy or law
-
D.
All of the above
Correct answer: D.
Chocks should be used when required to prevent vehicle movement.
Question 23 of 25 · Warning Devices
The low air pressure warning device must come on when air pressure in the service tanks falls below:
-
A.
80 psi
-
B.
60 psi
-
C.
50 psi or 1/2 the compressor governor cut-out pressure
-
D.
20 psi
Correct answer: C.
Low pressure warnings activate at 60 psi or less (or half the cut-out pressure on older vehicles).
Question 24 of 25 · Foundation Brakes
What's the most common type of foundation brake found on heavy vehicles?
-
A.
Disc brakes
-
B.
Wedge drum brakes
-
C.
S-cam drum brakes
-
D.
Air-over-hydraulic
Correct answer: C.
S-cam drum brakes are the most common foundation brakes on heavy commercial vehicles.
Question 25 of 25 · Bobtail
What is bobtail braking?
-
A.
Braking with no trailer attached, when the tractor brakes harder than usual
-
B.
A type of trailer-only braking
-
C.
Emergency braking on doubles
-
D.
A way to test the parking brake
Correct answer: A.
A bobtail tractor (without a trailer) brakes hard because it has less weight on the drive axles.
About the Air Brakes Test
The Air Brakes test covers air brake system parts (compressor, governor, reservoirs, drain valves, alcohol evaporator, safety valve, brake pedal, foundation brakes), dual air brake systems, inspecting air brakes, using air brakes (normal stops, emergency stops, parking brakes), and proper procedures for braking on downgrades. If you fail or skip the Air Brakes test, your CDL is restricted to vehicles without full air brake systems.
The Vermont Department of Motor Vehicles administers this knowledge test as part of its commercial driver license program. To earn the Air Brakes Endorsement on your Vermont CDL, you need to score at least 20 out of 25 on the official version.
Topics covered on this practice test
- Inspection: 5 questions
- Speed Management: 3 questions
- Compressor: 3 questions
- Spring Brakes: 2 questions
- ABS: 2 questions
- Foundation Brakes: 2 questions
- Gauges: 2 questions
- Combination Air: 1 question
- System Basics: 1 question
- Emergency Maneuvers: 1 question
- Parking: 1 question
- Warning Devices: 1 question
- Bobtail: 1 question
How to use this practice test
- Read each question carefully. CDL questions are written precisely — small wording differences matter.
- Click "Show Answers & Explanations" only after answering every question. Don't peek mid-test.
- Read the explanation for every question, even ones you got right. The reasoning is more important than the answer.
- Repeat the test until you score 100%. The questions are deterministic per state, so you can track your improvement over multiple sessions.
- Move on to the other endorsement tests for Vermont until you're ready for the official exam.
Tips specific to the Air Brakes test
Air Brakes questions test your ability to identify components, follow inspection sequences, and respond to system failures. Memorize the cut-in and cut-out pressures, the low-pressure warning thresholds, the pressure ranges at which spring brakes apply, and the maximum allowable air-loss rates. Many questions have nearly-identical wording, so precision matters.
Other practice tests for Vermont