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NM · GK (Class A) Endorsement

New Mexico Combination Vehicles CDL Practice Test

Below are 25 exam-style questions for the New Mexico Combination Vehicles CDL knowledge test, modeled on the FMCSA-aligned content used by the New Mexico Motor Vehicle Division. 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
A "trailer skid" usually starts because:
  • A The fifth wheel breaks
  • B The trailer brakes lock up
  • C The tractor brakes lock up
  • D A wheel bearing fails
Correct answer: B
Locking the trailer brakes is the most common cause of a trailer skid (jackknife).
Question 2 of 25
Glad hands are:
  • A Brake adjustment levers
  • B Manual transmission shifters
  • C Electrical connectors
  • D Coupling devices for connecting tractor air lines to the trailer
Correct answer: D
Glad hands have rubber seals and a metal coupler that joins the tractor and trailer air lines.
Question 3 of 25
When a tractor pulls a trailer with brakes that are out of balance:
  • A Stopping distances increase and the trailer can swing
  • B Steering becomes easier
  • C Stopping distances are normal
  • D No effect on safety
Correct answer: A
Brake imbalance makes the rig pull, lengthens stopping distance, and increases the chance of trailer swing.
Question 4 of 25
When the trailer brakes are operating but pulling weakly, this can indicate:
  • A Air leakage in the supply line, low pressure, or a brake-balance issue
  • B Cargo placement
  • C Driver fatigue
  • D Engine wear
Correct answer: A
Weak trailer brakes are usually an air-system problem and require diagnosis before continuing.
Question 5 of 25
Combination vehicles are usually harder to drive than single CMVs because:
  • A They take more skill to back, couple, and uncouple
  • B All of the above
  • C They are heavier and longer
  • D They have a higher rollover risk
Correct answer: B
All three factors apply. The Combination Vehicles section of the federal manual emphasizes the higher skill needed.
Question 6 of 25
You should test the air-brake system by:
  • A Listening to the brake light
  • B Pressing the pedal once at startup
  • C Asking a mechanic
  • D Performing the seven-step air-brake check before each trip
Correct answer: D
The seven-step check is the standard pre-trip air-brake test.
Question 7 of 25
A combination vehicle with empty trailers:
  • A Stops only with parking brake
  • B Stops faster than when loaded
  • C May actually take longer to stop because brakes are designed for the loaded weight
  • D Stops in the same distance
Correct answer: C
Empty trailers can lock up easily and skid, which counterintuitively increases stopping distance.
Question 8 of 25
The seven-pin connector on a tractor-trailer carries:
  • A Air for the brakes
  • B Hydraulic fluid
  • C Fuel
  • D Electrical power for trailer lights and ABS
Correct answer: D
The seven-pin (or older five-pin) is electrical, supplying lights, brake-light signal, and ABS.
Question 9 of 25
Tracking refers to:
  • A Cargo placement
  • B Lane positioning at intersections
  • C The fuel mileage
  • D The trailer following the same path as the tractor in a straight line
Correct answer: D
Tracking is how well the trailer follows the tractor; misalignment can indicate suspension or tire problems.
Question 10 of 25
The trailer hand valve operates:
  • A The parking brake
  • B The tractor service brakes only
  • C The trailer service brakes only
  • D Both tractor and trailer brakes simultaneously
Correct answer: C
The hand valve applies only the trailer service brakes. It is for testing — not for parking or routine use.
Question 11 of 25
When inspecting the air lines between tractor and trailer, look for:
  • A Cuts, abrasions, and worn seals
  • B Loose lug nuts only
  • C Engine oil leaks
  • D Cargo placement
Correct answer: A
Air-line condition is a typical roadside inspection focus on combinations.
Question 12 of 25
When you drive a combination vehicle, watch for:
  • A All of the above
  • B Off-tracking on right turns
  • C Trailer sway in crosswinds
  • D Reduced visibility along the trailer
Correct answer: A
All three are routine combination-vehicle considerations.
Question 13 of 25
Off-tracking means:
  • A Driving off the road
  • B Loss of traction
  • C The trailer wheels follow a tighter arc than the tractor wheels in a turn
  • D Sliding sideways
Correct answer: C
In a right turn, the trailer wheels cut the corner. To compensate, the tractor must swing wider.
Question 14 of 25
The fifth-wheel locking lever should be:
  • A Released and visible after coupling
  • B Locked and the safety latch in place after coupling
  • C Removed before driving
  • D Tied with rope
Correct answer: B
After backing under, the locking jaws must close around the kingpin and the safety latch must be in place.
Question 15 of 25
A safe combination-vehicle following distance is at least:
  • A One second per 10 feet of vehicle length below 40 mph, plus one extra second above 40 mph
  • B A vehicle length
  • C Two car lengths
  • D No specific rule
Correct answer: A
A 60-ft combination needs at least 6 seconds under 40 mph, 7 seconds above 40 mph.
Question 16 of 25
When you make a wide right turn, you should:
  • A Stay in the right lane and swing the front of the tractor wide enough to clear the curb without inviting cars to pass on the right
  • B Use the shoulder
  • C Turn from the left lane
  • D Stop traffic by signaling left
Correct answer: A
Use only as much room as needed and keep the right side blocked to following vehicles.
Question 17 of 25
The "service" line on a tractor-trailer:
  • A Carries electrical power
  • B Sends air pressure to apply trailer service brakes
  • C Drains the trailer reservoir
  • D Sends supply air to the trailer reservoirs
Correct answer: B
The service line carries braking-pressure changes from the foot valve to the trailer brakes.
Question 18 of 25
The proper test of a good fifth-wheel coupling is:
  • A Tug the trailer with the trailer parking brakes set
  • B Look at the locking jaws only
  • C Honk the horn
  • D Listen for a click
Correct answer: A
After coupling and locking, gently pull forward against the locked trailer brakes to confirm engagement.
Question 19 of 25
When backing into a dock, you should:
  • A Back at full speed
  • B Have the dispatcher in the cab
  • C Use only mirrors
  • D GOAL — Get Out And Look — and walk around the trailer first
Correct answer: D
A walk-around catches obstacles, people, and overhead clearance issues before you back.
Question 20 of 25
The proper sequence for uncoupling is generally:
  • A No specific order is required
  • B Pull tractor away first, then disconnect lines
  • C Lower landing gear, disconnect lines, release fifth wheel, pull tractor away
  • D Release fifth wheel first, then connect lines
Correct answer: C
Lower the landing gear, chock the wheels, disconnect air and electrical lines and stow them, release the fifth wheel, then slowly pull the tractor forward.
Question 21 of 25
When uncoupling, after the tractor is clear, you should:
  • A Connect the lines back to the tractor
  • B Disable the trailer parking brake
  • C Check that the trailer is stable on its landing gear
  • D Move the tractor far away immediately without checking
Correct answer: C
Verify the trailer is sitting solidly before leaving the area.
Question 22 of 25
Most rear-end collisions caused by combination vehicles result from:
  • A Driving too fast for conditions and/or too closely
  • B Engine failure
  • C Cargo movement
  • D Worn out tires
Correct answer: A
Speed and following distance dominate the causes. Increase cushion and slow down.
Question 23 of 25
If you cross the air lines (service to emergency and vice versa) when coupling:
  • A The horn will sound
  • B You will notice immediately because trailer brakes will not work properly
  • C Nothing will happen
  • D The trailer brakes will be locked on
Correct answer: B
Crossed glad hands often produce no air flow to brake chambers and incorrect brake operation; you should notice on the brake test.
Question 24 of 25
During a brake check before moving, you should look for:
  • A Pulling, sticking, or unusual feel as you apply the brakes
  • B Engine knocking
  • C Steering wander only
  • D Smoke from the cab
Correct answer: A
Low-speed brake test identifies pulling, sticking, or weakness so you don't discover it on the highway.
Question 25 of 25
The trailer hand valve should NOT be used to:
  • A Apply trailer brakes momentarily
  • B Test the trailer brakes
  • C Both for parking and to prevent jackknife
  • D Hold the vehicle when parking
Correct answer: C
Don't use it to park (it can leak off) or to prevent a jackknife (it locks the trailer wheels and worsens the skid).

Study tips for the New Mexico Combination Vehicles exam

The Combination Vehicles portion of the New Mexico CDL exam is graded out of the bank of questions the New Mexico Motor Vehicle Division draws from each year. While the exact bank is not published, every question is sourced from the Combination Vehicles chapter of the New Mexico 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 Mexico 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 Combination Vehicles.

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 Mexico Motor Vehicle Division 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 Combination Vehicles 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 Mexico General Knowledge practice test before scheduling the real exam.

Next steps

Missed more than four questions? Re-read the Combination Vehicles study guide and the matching chapter in the official New Mexico 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 Mexico Motor Vehicle Division office.

Already comfortable with this endorsement? Drill another: NM General Knowledge · NM Air Brakes · NM Hazardous Materials · NM Passenger · NM School Bus · NM Tank Vehicle · NM Doubles / Triples

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