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Vermont Air Brakes CDL Practice Test

Below are 25 exam-style questions for the Vermont Air Brakes CDL knowledge test, modeled on the FMCSA-aligned content used by the Vermont Department of Motor Vehicles. Try to answer each question on your own before reading the answer key directly under it. The questions and answer choices are shuffled deterministically per state and endorsement, so the order will stay the same on repeat visits — that lets you genuinely measure your improvement.

Heads up: this is a study tool, not a graded exam. Cover the answer with your hand or a sheet of paper for an honest practice run, then re-read the explanations for any questions you missed. Aim for 22 out of 25 or better, three times in a row, before scheduling the real exam.
Question 1 of 25
Air pressure should normally build from 50 to 90 psi within:
  • A About 3 minutes in dual systems
  • B 10 minutes
  • C Less than 30 seconds
  • D It does not matter
Correct answer: A
Dual air systems should build from 50 to 90 psi within about 3 minutes at idle.
Question 2 of 25
The air compressor is driven by:
  • A The electrical system
  • B The transmission
  • C The exhaust system
  • D The engine, by belts or directly geared
Correct answer: D
Compressors are typically engine-driven, either by a belt or direct gearing, so air pressure builds whenever the engine runs.
Question 3 of 25
Which is true about air storage tanks?
  • A They must be drained completely once a year
  • B They drain themselves automatically in all trucks
  • C They must be drained daily to remove water and oil
  • D They never need to be drained
Correct answer: C
Most trucks require manual daily draining of each tank. Some have automatic moisture ejectors, but the driver is still responsible.
Question 4 of 25
Each axle group on an air-brake-equipped vehicle has its own:
  • A Drive shaft
  • B Set of brake chambers
  • C Air compressor
  • D Engine
Correct answer: B
Each axle group has its own brake chambers fed by the air system; one compressor supplies all of them.
Question 5 of 25
Modulating valves on the rear axle help prevent:
  • A Wheel lockup during emergency braking
  • B Steering wander
  • C Engine overheating
  • D Tire blowouts
Correct answer: A
Modulating valves and ABS sensors release pressure briefly to keep wheels from locking.
Question 6 of 25
The air-brake hand valve (trolley valve) operates:
  • A Both tractor and trailer brakes
  • B The parking brake
  • C The trailer service brakes only
  • D The tractor service brakes only
Correct answer: C
The hand valve applies only the trailer service brakes. It is not a parking brake or a substitute for the foot brake.
Question 7 of 25
Anti-lock braking systems (ABS) on air-brake vehicles:
  • A Are optional and rarely installed
  • B Are required only on hazmat trailers
  • C Help prevent wheel lockup but do not necessarily shorten stopping distance
  • D Replace foundation brakes
Correct answer: C
ABS helps the driver maintain steering control by preventing wheel lockup. It does not necessarily reduce stopping distance.
Question 8 of 25
When doing the air-leak rate test, the engine should be:
  • A Off, with brakes released for the first part
  • B Running at high RPM
  • C Started and stopped repeatedly
  • D In gear
Correct answer: A
Engine off, brakes released to test static leak rate; then brakes applied and held for the second part.
Question 9 of 25
Brake drums in good condition will:
  • A Be glowing red after stops
  • B Have small cracks
  • C Be free of cracks longer than half the width of the friction area
  • D Be coated with oil
Correct answer: C
Cracks longer than half the friction area or any visible heat checks usually fail inspection.
Question 10 of 25
Front-wheel brakes are required on commercial vehicles because:
  • A They look balanced
  • B Federal law mandates them as decorative
  • C They reduce stopping distance significantly without normally causing skids on dry pavement
  • D They make steering easier
Correct answer: C
Front brakes provide a large share of stopping force and modern vehicles are designed so they do not cause front-wheel skids on dry pavement.
Question 11 of 25
In a dual system, normal cut-in pressure is approximately:
  • A 85 psi
  • B 40 psi
  • C 60 psi
  • D 125 psi
Correct answer: C
Cut-in is usually around 100 psi but cut-out is around 125 psi. Cut-in below 60 psi indicates a problem in many systems.
Question 12 of 25
A driver should never:
  • A Use the trailer hand valve as a parking brake
  • B Make pre-trip inspections
  • C Test the parking brake
  • D Drain the wet tank
Correct answer: A
The trailer hand valve is not a parking device — see the trailer-hand-valve question. Always set the trailer parking brakes.
Question 13 of 25
You should test the trailer service brakes by:
  • A Listening for a hiss
  • B Releasing the parking brakes, moving the vehicle slowly forward, and applying the trailer hand valve
  • C Pumping them while parked
  • D Looking at the gauge
Correct answer: B
A low-speed pull-and-stop with the trailer hand valve confirms the trailer brakes apply on their own.
Question 14 of 25
The proper braking technique on a long downgrade is:
  • A Heavy continuous braking
  • B Light, intermittent braking with engine braking and a low gear
  • C Coast in neutral
  • D Apply the parking brake
Correct answer: B
Use the proper low gear so engine braking does most of the work; brief, moderate brake applications keep the speed in check.
Question 15 of 25
Air dryers are used in air-brake systems to:
  • A Remove moisture and contaminants from the compressed air
  • B Increase pressure
  • C Replace governors
  • D Cool the air before it enters the brake chambers
Correct answer: A
Dryers reduce moisture in the air system, helping prevent corrosion, ice in winter, and contamination.
Question 16 of 25
After making the initial brake application, the air-pressure drop should not exceed:
  • A 5 psi
  • B 2-3 psi
  • C 10 psi
  • D 1 psi
Correct answer: B
A small initial drop is normal as the system equalizes — but excessive drop indicates a leak.
Question 17 of 25
When the air pressure in the brake system drops too low:
  • A Nothing happens until you stop
  • B The trailer hand valve releases
  • C Spring brakes apply automatically
  • D The engine stops
Correct answer: C
When system pressure drops, typically below 20-45 psi, mechanical springs apply the brakes regardless of driver input.
Question 18 of 25
Brake-lag distance for a CMV traveling 55 mph is approximately:
  • A 32 feet
  • B 0 feet
  • C 142 feet
  • D 300 feet
Correct answer: A
About 32 feet at 55 mph for the brake lag alone — added to reaction and braking distances.
Question 19 of 25
When the parking brake is set, the dashboard valve will normally:
  • A Have no indication
  • B Flash red
  • C Stay pushed in
  • D Stay popped out and yellow
Correct answer: D
Yellow diamond-shaped valves stay out (popped) when parking brakes are applied; pushing them in releases the brakes.
Question 20 of 25
Spring brakes do NOT replace:
  • A The tail lights
  • B The horn
  • C The headlights
  • D The service brakes for normal stops
Correct answer: D
Spring brakes are for parking and emergency only — never for normal service braking.
Question 21 of 25
Spring brakes are held off by:
  • A Engine vacuum
  • B Electrical current
  • C Hydraulic pressure
  • D Air pressure
Correct answer: D
Compressed air holds the springs back. When air pressure drops, the springs apply the brakes mechanically.
Question 22 of 25
After releasing the parking brake on a tractor, you should:
  • A Drain the wet tank
  • B Pump the service brake five times
  • C Wait for full system pressure before moving
  • D Drive immediately
Correct answer: C
Make sure the system reaches at least the cut-out pressure (typically around 120 psi) before driving.
Question 23 of 25
You should not over-tighten a glad-hand because:
  • A It violates federal weight law
  • B It will reduce engine power
  • C It can damage the rubber seals
  • D It is bad luck
Correct answer: C
Over-tightening crushes the seals. The connection should be firm but not forced.
Question 24 of 25
You should test the parking brake by:
  • A Pressing the service brake while parked
  • B Driving over a curb
  • C Setting the parking brake, releasing the service brake, and gently trying to move the vehicle
  • D Doing nothing — the dashboard light is enough
Correct answer: C
Apply throttle gently in low gear; if the truck moves, the parking brake is not holding.
Question 25 of 25
A dual air-brake system means:
  • A Two separate air-brake systems on one set of brake controls
  • B Twice the air pressure
  • C Two compressors
  • D Two governors
Correct answer: A
Modern trucks have two separate air systems (often labeled primary and secondary) with one set of brake controls so a failure in one circuit still leaves working brakes.

Study tips for the Vermont Air Brakes exam

The Air Brakes portion of the Vermont CDL exam is graded out of the bank of questions the Vermont Department of Motor Vehicles draws from each year. While the exact bank is not published, every question is sourced from the Air Brakes chapter of the Vermont CDL handbook, which itself is derived from the FMCSA Model Commercial Driver's License Manual. That means studying our practice tests, reading the corresponding handbook chapter, and re-reading the parts you got wrong is genuinely the most efficient route to a first-time pass.

Most successful applicants follow a simple cycle: take the practice test cold, write down every question you missed, open the matching chapter of the official Vermont handbook, re-read the section that contains the right answer, then re-take the practice test 24 to 48 hours later. The 24-hour delay matters — sleep is when your brain commits new information to long-term memory, and CDL knowledge questions reward that kind of consolidated learning rather than cramming.

Pay particular attention to questions that include qualifier words like always, never, only, primary, or most. CDL test writers love to flip the right answer with a single qualifier. When two answer choices look almost identical, pay attention to the verb (is it must, should, or may?) and to any numbers (14 days, 100 air miles, 8 hours, 70/8 split). On endorsement tests in particular, watch for trick framing where a true statement about a different endorsement is offered as the "correct" answer to a question that is actually about Air Brakes.

Test-day logistics matter too. Bring photo ID, your Social Security card or birth certificate, your medical examiner's certificate (DOT card), and proof of state residency if you haven't already submitted those documents. The Vermont Department of Motor Vehicles will not let you sit for the knowledge exam without your documentation, and most offices charge an additional fee for re-attempts. Arrive early — the wait at most CDL testing offices runs 30 to 60 minutes — and silence your phone before the exam begins.

Finally, keep your General Knowledge fundamentals sharp even when you're focused on the Air Brakes exam. Many states administer multiple knowledge tests in a single sitting, and questions on weight definitions (GVWR, GCWR, GAWR), stopping distance, and the pre-trip inspection routine show up across endorsements. If you're unsure on the basics, sit a fresh Vermont General Knowledge practice test before scheduling the real exam.

Next steps

Missed more than four questions? Re-read the Air Brakes study guide and the matching chapter in the official Vermont CDL handbook. Then come back and re-take the test. Once you can score 22 of 25 or higher on three runs in a row, you're in good shape to schedule the real exam at your local Vermont Department of Motor Vehicles office.

Already comfortable with this endorsement? Drill another: VT General Knowledge · VT Combination Vehicles · VT Hazardous Materials · VT Passenger · VT School Bus · VT Tank Vehicle · VT Doubles / Triples

New to the CDL process in Vermont? Read How to apply for a CDL in Vermont for the document checklist and step-by-step timeline.