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TX · GK (Class A) Endorsement

Texas Combination Vehicles CDL Practice Test

Below are 25 exam-style questions for the Texas Combination Vehicles CDL knowledge test, modeled on the FMCSA-aligned content used by the Texas Department of Public Safety. 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
Off-tracking means:
  • A Loss of traction
  • B Driving off the road
  • 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 2 of 25
A heavy combination vehicle in a curve is most likely to:
  • A Lose engine power
  • B Spin out
  • C Roll over before sliding
  • D Stop suddenly
Correct answer: C
Loaded trailers reach the rollover threshold before they slide. Slow before the curve.
Question 3 of 25
Which of the following can damage a fifth wheel?
  • A Failure to grease
  • B Coupling with the trailer too high
  • C All of the above
  • D Backing too fast
Correct answer: C
All three: high trailer skips the jaws, fast backing impacts hardware, and lack of lubrication accelerates wear.
Question 4 of 25
The proper sequence for uncoupling is generally:
  • A No specific order is required
  • B Release fifth wheel first, then connect lines
  • C Pull tractor away first, then disconnect lines
  • D Lower landing gear, disconnect lines, release fifth wheel, pull tractor away
Correct answer: D
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 5 of 25
A tractor jackknife happens when:
  • A The tractor parking brake fails
  • B The drive wheels lose traction and the tractor begins to slide
  • C The trailer is too heavy
  • D The fifth wheel disengages
Correct answer: B
A drive-wheel skid causes the tractor to swing into the trailer at an angle.
Question 6 of 25
A converter dolly:
  • A Is part of the tractor
  • B Is used to convert a semitrailer into a full trailer for towing in combination
  • C Is used only when triple-towing
  • D Replaces the fifth wheel on the tractor
Correct answer: B
A converter dolly turns a semitrailer into a full trailer that can be coupled behind another trailer.
Question 7 of 25
When a tractor pulls a trailer with brakes that are out of balance:
  • A Steering becomes easier
  • B Stopping distances are normal
  • C No effect on safety
  • D Stopping distances increase and the trailer can swing
Correct answer: D
Brake imbalance makes the rig pull, lengthens stopping distance, and increases the chance of trailer swing.
Question 8 of 25
Trailer ABS uses:
  • A Hand valves
  • B Sensors at each wheel that release brake pressure when wheel lockup is detected
  • C A separate compressor
  • D Hydraulic brakes
Correct answer: B
Wheel-speed sensors trigger valves to release pressure when lockup is detected.
Question 9 of 25
A "trailer skid" usually starts because:
  • A The fifth wheel breaks
  • B The tractor brakes lock up
  • C The trailer brakes lock up
  • D A wheel bearing fails
Correct answer: C
Locking the trailer brakes is the most common cause of a trailer skid (jackknife).
Question 10 of 25
The fifth-wheel locking lever should be:
  • A Locked and the safety latch in place after coupling
  • B Removed before driving
  • C Released and visible after coupling
  • D Tied with rope
Correct answer: A
After backing under, the locking jaws must close around the kingpin and the safety latch must be in place.
Question 11 of 25
Most rear-end collisions caused by combination vehicles result from:
  • A Driving too fast for conditions and/or too closely
  • B Cargo movement
  • C Worn out tires
  • D Engine failure
Correct answer: A
Speed and following distance dominate the causes. Increase cushion and slow down.
Question 12 of 25
During a brake check before moving, you should look for:
  • A Smoke from the cab
  • B Pulling, sticking, or unusual feel as you apply the brakes
  • C Engine knocking
  • D Steering wander only
Correct answer: B
Low-speed brake test identifies pulling, sticking, or weakness so you don't discover it on the highway.
Question 13 of 25
Before pulling the kingpin release lever to uncouple, you must:
  • A Honk the horn
  • B Drain the air tanks
  • C Lower the trailer landing gear and chock the trailer wheels
  • D Disconnect the electrical line first
Correct answer: C
Always lower the landing gear and chock the trailer so it cannot move once you pull out from under it.
Question 14 of 25
When parking a tractor-trailer, you should:
  • A Set only the tractor parking brake
  • B Leave the engine running with the brakes off
  • C Use the trailer hand valve
  • D Set both tractor and trailer parking brakes
Correct answer: D
For full parking, both parking brakes apply.
Question 15 of 25
When inspecting the air lines between tractor and trailer, look for:
  • A Cargo placement
  • B Loose lug nuts only
  • C Engine oil leaks
  • D Cuts, abrasions, and worn seals
Correct answer: D
Air-line condition is a typical roadside inspection focus on combinations.
Question 16 of 25
The trailer landing gear (dolly legs) should be:
  • A Always halfway extended
  • B Lowered to the ground while driving
  • C Disconnected before driving
  • D Fully raised before driving
Correct answer: D
Landing gear must be fully raised and the crank handle secured before moving the trailer.
Question 17 of 25
Tracking refers to:
  • A The trailer following the same path as the tractor in a straight line
  • B Lane positioning at intersections
  • C The fuel mileage
  • D Cargo placement
Correct answer: A
Tracking is how well the trailer follows the tractor; misalignment can indicate suspension or tire problems.
Question 18 of 25
When backing into a dock, you should:
  • A Back at full speed
  • B GOAL — Get Out And Look — and walk around the trailer first
  • C Have the dispatcher in the cab
  • D Use only mirrors
Correct answer: B
A walk-around catches obstacles, people, and overhead clearance issues before you back.
Question 19 of 25
Sharp turns at low speed will cause:
  • A Off-tracking — the trailer wheels follow a tighter arc than the tractor
  • B No off-tracking
  • C Brake fade
  • D Wheel damage
Correct answer: A
Off-tracking always happens; sharper turns make it worse.
Question 20 of 25
If you cross the air lines (service to emergency and vice versa) when coupling:
  • A You will notice immediately because trailer brakes will not work properly
  • B Nothing will happen
  • C The trailer brakes will be locked on
  • D The horn will sound
Correct answer: A
Crossed glad hands often produce no air flow to brake chambers and incorrect brake operation; you should notice on the brake test.
Question 21 of 25
When you cross a railroad track in a combination vehicle, the safest practice is:
  • A Honk and accelerate
  • B Shift in the middle of the track
  • C Stop on the tracks if traffic ahead slows
  • D Cross in a low gear without shifting
Correct answer: D
Cross in a low gear without shifting; never stop on the tracks; never shift in the middle.
Question 22 of 25
When backing a tractor-trailer, you should:
  • A Back without using mirrors
  • B Always back to the right
  • C Back to the left whenever possible because you can see better
  • D Back as fast as practical
Correct answer: C
Backing to the driver's side gives the best view of the trailer. Always GOAL — Get Out And Look — before and during.
Question 23 of 25
You should never back under a trailer that is:
  • A Empty
  • B Too high — it can damage the kingpin or skip over the fifth wheel
  • C Properly chocked
  • D Loaded
Correct answer: B
A trailer set too high can skip over the fifth-wheel jaws and not lock, or damage the coupling.
Question 24 of 25
Trailer air supply valves on tractors are typically:
  • A Round, blue, marked TRACTOR
  • B Octagonal, red, marked TRAILER AIR SUPPLY
  • C Square, white, marked CHARGE
  • D Triangular, green, marked SERVICE
Correct answer: B
The trailer air-supply valve is the red, octagonal knob — a federal standard.
Question 25 of 25
When coupling a tractor to a semitrailer, the trailer should be at:
  • A Whatever height it happens to be
  • B Maximum legal height
  • C A height where the tractor will lift the trailer slightly when backing under
  • D A height that requires the tractor to drop down to fit
Correct answer: C
The trailer should be slightly lower than the fifth wheel so backing in lifts the trailer.

Study tips for the Texas Combination Vehicles exam

The Combination Vehicles portion of the Texas CDL exam is graded out of the bank of questions the Texas Department of Public Safety draws from each year. While the exact bank is not published, every question is sourced from the Combination Vehicles chapter of the Texas 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 Texas 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 Texas Department of Public Safety 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 Texas 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 Texas 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 Texas Department of Public Safety office.

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

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