25 realistic Air Brakes practice questions for Rhode Island CDL applicants. Required for: Vehicles equipped with air brake systems. Official test: 25 questions, 20 correct to pass.
Question 1 of 25 · Parking
On a tractor with no trailer attached, the tractor parking brake control:
-
A.
Will lock and unlock the front brakes
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B.
Will set or release the spring brakes on the tractor
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C.
Has no function
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D.
Operates only the trailer brakes
Correct answer: B.
The yellow diamond control sets and releases the tractor parking (spring) brakes.
Question 2 of 25 · Operation
When making a normal stop, what should you do?
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A.
Push the brake pedal down so you can stop at a safe place and remain in control
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B.
Pump the brakes
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C.
Use only the parking brake
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D.
Use only the trailer hand valve
Correct answer: A.
Apply pressure progressively to come to a smooth, safe stop while maintaining control.
Question 3 of 25 · Inspection
Air leaks during a static brake check could indicate:
-
A.
Faulty brake chambers or air lines
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B.
Engine problems
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C.
Bad tires
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D.
Low fuel pressure
Correct answer: A.
Air leaks usually indicate faulty chambers, lines, fittings, or valves.
Question 4 of 25 · Compressor
What is the purpose of a one-way check valve?
-
A.
Allow air to flow in one direction
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B.
Allow water to drain
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C.
Prevent the trailer from moving
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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 5 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
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B.
60 psi
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C.
50 psi or 1/2 the compressor governor cut-out pressure
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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 6 of 25 · Tanks
Air brake equipped vehicles must have:
-
A.
Only an emergency brake
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B.
A drain valve in each air tank
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C.
Hydraulic backup
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D.
Disc brakes only
Correct answer: B.
Each air tank has a drain valve to remove water and oil that collect in the tank.
Question 7 of 25 · Emergency Maneuvers
Which of these statements is true about emergency braking?
-
A.
Pumping the brakes is always best
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B.
Stab braking is for non-ABS vehicles in emergencies
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C.
You should brake harder than necessary
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D.
Stab braking is the same as pumping
Correct answer: B.
Stab braking applies to non-ABS systems: full application until lockup, then release.
Question 8 of 25 · Gauges
The supply pressure gauge tells you:
-
A.
The pressure of brake fluid
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B.
How much air pressure is in the air tanks
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C.
The trailer brake pressure
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D.
The temperature of the brake
Correct answer: B.
The supply gauge shows the air pressure available in the storage tanks.
Question 9 of 25 · Inspection
Which of the following must be checked before operating an air-braked vehicle?
-
A.
Low air pressure warning signal
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B.
Spring brakes set automatically
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C.
Air leakage rate
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D.
All of the above
Correct answer: D.
All of these are required pre-trip air brake checks.
Question 10 of 25 · Speed Management
Air brake lag is:
-
A.
The time required for the brakes to apply after the pedal is pressed
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B.
The amount of free play in the brake pedal
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C.
The distance traveled before the brakes release
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D.
The time to drain air tanks
Correct answer: A.
Lag is the time between pressing the pedal and the brakes actually applying — about 0.4 seconds.
Question 11 of 25 · Inspection
How much air pressure (psi) loss is allowed per minute for combination vehicles with the engine off and brakes released?
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A.
Up to 1 psi
-
B.
Up to 2 psi
-
C.
Up to 3 psi
-
D.
Up to 4 psi
Correct answer: B.
Combination vehicles allow up to 3 psi loss per minute with brakes released; with brakes applied, up to 4 psi.
Question 12 of 25 · Spring Brakes
What does the term "modulating control valve" refer to?
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A.
A valve to regulate engine RPM
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B.
A hand-operated valve that gradually applies the spring brakes
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C.
A device that drains air tanks
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D.
The trailer hand valve
Correct answer: B.
A modulating control valve allows gradual application of spring brakes for emergency or backup use.
Question 13 of 25 · System Basics
Air brakes use compressed air to:
-
A.
Lubricate the wheels
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B.
Make the brakes work
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C.
Cool the engine
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D.
Increase fuel pressure
Correct answer: B.
Compressed air is the working fluid that applies the brakes in an air brake system.
Question 14 of 25 · Spring Brakes
Where are spring brakes typically NOT found?
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A.
Front steering axle
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B.
Drive axles
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C.
Trailer axles
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D.
Tractor rear axles
Correct answer: A.
Spring brakes are found on drive axles and trailer axles, not normally on the steering axle.
Question 15 of 25 · Operation
When the brake pedal is pushed harder, what happens?
-
A.
Brake pedal must be pumped to release
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B.
More air goes to the brakes; less foot pressure releases air
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C.
It locks the brakes permanently
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D.
The brakes do not respond
Correct answer: B.
The harder you push, the more air pressure is sent to the brake chambers.
Question 16 of 25 · System Basics
Air brake systems combine three different braking systems. They are:
-
A.
Service, parking, and emergency brakes
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B.
Hydraulic, parking, and emergency brakes
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C.
Front, rear, and trailer brakes
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D.
Disc, drum, and parking brakes
Correct answer: A.
The three are: the service brake, the parking brake, and the emergency brake.
Question 17 of 25 · Gauges
What gauge tells you the air pressure being delivered to the brakes?
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A.
Application pressure gauge
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B.
Supply pressure gauge
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C.
Speedometer
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D.
Tachometer
Correct answer: A.
The application gauge shows pressure being applied to the brakes when the pedal is pressed.
Question 18 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 19 of 25 · Inspection
How do you know that you have an air leak?
-
A.
Pressure drops faster than allowable rate
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B.
You hear hissing
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C.
Both A and B
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D.
The brake pedal feels firm
Correct answer: C.
Pressure dropping faster than allowed and audible hissing both indicate leaks.
Question 20 of 25 · System Basics
Which of these is NOT a part of the basic air brake system?
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A.
Air compressor
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B.
Air storage tanks
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C.
Hydraulic master cylinder
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D.
Foot brake valve
Correct answer: C.
Hydraulic master cylinders belong to hydraulic brake systems, not air brake systems.
Question 21 of 25 · Spring Brakes
What does a "spring brake" mean?
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A.
A brake that operates only in spring weather
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B.
A mechanical brake that uses powerful springs to apply the brake when air pressure is lost
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C.
A specific kind of disc brake
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D.
A backup hydraulic brake
Correct answer: B.
Spring brakes use powerful coil springs to apply the brakes when air pressure is lost.
Question 22 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 23 of 25 · Foundation Brakes
What's the most common type of foundation brake found on heavy vehicles?
-
A.
Disc brakes
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B.
Wedge drum brakes
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C.
S-cam drum brakes
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D.
Air-over-hydraulic
Correct answer: C.
S-cam drum brakes are the most common foundation brakes on heavy commercial vehicles.
Question 24 of 25 · Foundation Brakes
When checking the slack adjuster on S-cam brakes, the slack adjuster should not move more than:
-
A.
1/2 inch
-
B.
1 inch
-
C.
About 1 inch where the push rod attaches to it
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D.
2 inches
Correct answer: C.
When pulled by hand, the slack adjuster shouldn't move more than about an inch where the push rod attaches.
Question 25 of 25 · ABS
What is the proper procedure for an air brake stop in a vehicle equipped with ABS?
-
A.
Pump the brakes
-
B.
Press the brake pedal firmly and steadily; let ABS work
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C.
Disengage ABS first
-
D.
Apply the parking brake
Correct answer: B.
With ABS, brake firmly and steadily. ABS prevents wheel lockup automatically.
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 Rhode Island Division of Motor Vehicles administers this knowledge test as part of its commercial driver license program. To earn the Air Brakes Endorsement on your Rhode Island CDL, you need to score at least 20 out of 25 on the official version.
Topics covered on this practice test
- Inspection: 6 questions
- Spring Brakes: 3 questions
- System Basics: 3 questions
- Operation: 2 questions
- Gauges: 2 questions
- Foundation Brakes: 2 questions
- Parking: 1 question
- Compressor: 1 question
- Warning Devices: 1 question
- Tanks: 1 question
- Emergency Maneuvers: 1 question
- Speed Management: 1 question
- ABS: 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 Rhode Island 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.