NH · L (restriction removed) Endorsement

New Hampshire Air Brakes CDL Practice Test

Below are 25 exam-style questions for the New Hampshire Air Brakes CDL knowledge test, modeled on the FMCSA-aligned content used by the New Hampshire Division 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

Brake-lag distance for a CMV traveling 55 mph is approximately:

A 0 feet
B 142 feet
C 32 feet
D 300 feet

Correct answer: C

About 32 feet at 55 mph for the brake lag alone — added to reaction and braking distances.

Question 2 of 25

Air pressure should normally build from 50 to 90 psi within:

A 10 minutes
B It does not matter
C About 3 minutes in dual systems
D Less than 30 seconds

Correct answer: C

Dual air systems should build from 50 to 90 psi within about 3 minutes at idle.

Question 3 of 25

Cross-leakage between primary and secondary brake systems is:

A A serious defect that can prevent backup braking
B A normal feature
C Required by federal law
D Caused by overuse

Correct answer: A

Each circuit must remain independent so a failure in one still leaves the other working.

Question 4 of 25

Which is true about air storage tanks?

A They drain themselves automatically in all trucks
B They must be drained completely once a year
C They never need to be drained
D They must be drained daily to remove water and oil

Correct answer: D

Most trucks require manual daily draining of each tank. Some have automatic moisture ejectors, but the driver is still responsible.

Question 5 of 25

You should test the parking brake by:

A Setting the parking brake, releasing the service brake, and gently trying to move the vehicle
B Doing nothing — the dashboard light is enough
C Pressing the service brake while parked
D Driving over a curb

Correct answer: A

Apply throttle gently in low gear; if the truck moves, the parking brake is not holding.

Question 6 of 25

After parking a tractor-trailer:

A Set only the tractor parking brake
B Set both tractor and trailer parking brakes
C Leave both released
D Set only the trailer parking brake

Correct answer: B

Federal practice is to set both parking brakes when fully parked. The exception is during coupling/uncoupling, where the trailer brakes are set.

Question 7 of 25

A dual air-brake system means:

A Two separate air-brake systems on one set of brake controls
B Two compressors
C Two governors
D Twice the air pressure

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.

Question 8 of 25

In a dual system, normal cut-in pressure is approximately:

A 60 psi
B 40 psi
C 125 psi
D 85 psi

Correct answer: A

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 9 of 25

Glad-hand seals should be:

A Coated with oil
B Removed for inspection
C Free of dirt and damage and properly seated
D Loose for easy connection

Correct answer: C

Damaged or dirty seals cause leaks. Inspect and clean them as part of the trailer hookup.

Question 10 of 25

In a combination vehicle, with the brakes applied and the engine off, the maximum allowable air loss is:

A 4 psi per minute
B 3 psi per minute
C 2 psi per minute
D 5 psi per minute

Correct answer: A

Combination vehicle, brakes applied: 4 psi per minute. Single vehicle, brakes applied: 3 psi per minute.

Question 11 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 12 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 13 of 25

Modulating valves on the rear axle help prevent:

A Steering wander
B Wheel lockup during emergency braking
C Tire blowouts
D Engine overheating

Correct answer: B

Modulating valves and ABS sensors release pressure briefly to keep wheels from locking.

Question 14 of 25

After making the initial brake application, the air-pressure drop should not exceed:

A 1 psi
B 2-3 psi
C 10 psi
D 5 psi

Correct answer: B

A small initial drop is normal as the system equalizes — but excessive drop indicates a leak.

Question 15 of 25

If air pressure drops in the emergency line:

A Trailer service brakes apply
B Nothing happens
C Trailer spring brakes apply automatically
D Tractor brakes apply

Correct answer: C

Loss of supply-line pressure is the failsafe that triggers the trailer's spring brakes.

Question 16 of 25

A foot-valve pressure gauge reading lower than expected during a brake application could indicate:

A A leak or restriction
B A worn seat belt
C A new compressor
D Normal operation

Correct answer: A

Low pressure during application means the system isn't delivering full braking force — investigate.

Question 17 of 25

When testing low-air warning, you should:

A Pump the brake to fan down the pressure and verify the warning activates before pressure drops below 60 psi
B Look at the dashboard light
C Disconnect the trailer
D Drain the wet tank only

Correct answer: A

Fan the brakes (engine off) until the warning device activates and confirm it is above 60 psi.

Question 18 of 25

You should not over-tighten a glad-hand because:

A It will reduce engine power
B It can damage the rubber seals
C It violates federal weight law
D It is bad luck

Correct answer: B

Over-tightening crushes the seals. The connection should be firm but not forced.

Question 19 of 25

A common reason for compressor failure to keep up is:

A All of the above
B A leak in the brake system
C A clogged air filter or worn compressor
D A broken governor

Correct answer: A

Any of these causes can prevent the compressor from maintaining cut-out pressure.

Question 20 of 25

When approaching a long downgrade, you should:

A Coast in neutral
B Test the brakes by lightly applying them at the top
C Skip the brake test
D Test the brakes at the bottom

Correct answer: B

A light brake application at the top tests for pulling or weakness before the descent puts heat into the system.

Question 21 of 25

When the air pressure in the brake system drops too low:

A Nothing happens until you stop
B Spring brakes apply automatically
C The engine stops
D The trailer hand valve releases

Correct answer: B

When system pressure drops, typically below 20-45 psi, mechanical springs apply the brakes regardless of driver input.

Question 22 of 25

When a vehicle is hooked to a trailer, the air system must include:

A Only a safety chain
B Only an electrical connector
C One additional reservoir for the trailer brakes
D Service line and emergency line, with glad-hand connectors

Correct answer: D

Air goes through service and emergency (supply) lines to the trailer, with glad-hand connectors and color-coded couplers.

Question 23 of 25

The air-brake hand valve (trolley valve) operates:

A Both tractor and trailer brakes
B The trailer service brakes only
C The tractor service brakes only
D The parking brake

Correct answer: B

The hand valve applies only the trailer service brakes. It is not a parking brake or a substitute for the foot brake.

Question 24 of 25

Air-brake hoses should:

A Be coiled tightly under the truck
B Be wrapped in tape
C Show no signs of damage, leaks, or excessive wear
D Have at least 5 splices each

Correct answer: C

Damaged or chafed hoses are a common air-brake defect and a frequent out-of-service citation.

Question 25 of 25

A common practice during a long brake-recharge wait is to:

A Check the brake light visibility
B Disable the warning lamp
C Drain the wet tank
D Allow the system to reach operating pressure before driving

Correct answer: D

Always wait for full operating pressure (typically around 120 psi) before moving the vehicle.

Study tips for the New Hampshire Air Brakes exam

The Air Brakes portion of the New Hampshire CDL exam is graded out of the bank of questions the New Hampshire Division 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 New Hampshire 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 New Hampshire 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 New Hampshire Division 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 New Hampshire 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 New Hampshire 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 New Hampshire Division of Motor Vehicles office.

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

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