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CO · GK (Class A) Endorsement

Colorado Combination Vehicles CDL Practice Test

Below are 25 exam-style questions for the Colorado Combination Vehicles CDL knowledge test, modeled on the FMCSA-aligned content used by the Colorado Department of Revenue 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
A converter dolly:
  • A Replaces the fifth wheel on the tractor
  • B Is used only when triple-towing
  • C Is part of the tractor
  • D Is used to convert a semitrailer into a full trailer for towing in combination
Correct answer: D
A converter dolly turns a semitrailer into a full trailer that can be coupled behind another trailer.
Question 2 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 3 of 25
You should test the air-brake system by:
  • A Performing the seven-step air-brake check before each trip
  • B Asking a mechanic
  • C Pressing the pedal once at startup
  • D Listening to the brake light
Correct answer: A
The seven-step check is the standard pre-trip air-brake test.
Question 4 of 25
The "emergency" line (supply line) on a tractor-trailer:
  • A Carries electrical signals
  • B Drains the wet tank
  • C Sends supply air to the trailer reservoirs and controls the trailer emergency brakes
  • D Operates the parking brake only
Correct answer: C
Loss of pressure on the emergency line causes the trailer's emergency brake to apply automatically.
Question 5 of 25
Which of the following can damage a fifth wheel?
  • A All of the above
  • B Failure to grease
  • C Backing too fast
  • D Coupling with the trailer too high
Correct answer: A
All three: high trailer skips the jaws, fast backing impacts hardware, and lack of lubrication accelerates wear.
Question 6 of 25
When you cross a railroad track in a combination vehicle, the safest practice is:
  • A Honk and accelerate
  • B Cross in a low gear without shifting
  • C Stop on the tracks if traffic ahead slows
  • D Shift in the middle of the track
Correct answer: B
Cross in a low gear without shifting; never stop on the tracks; never shift in the middle.
Question 7 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 Move the tractor far away immediately without checking
  • D Check that the trailer is stable on its landing gear
Correct answer: D
Verify the trailer is sitting solidly before leaving the area.
Question 8 of 25
When inspecting the air lines between tractor and trailer, look for:
  • A Loose lug nuts only
  • B Cargo placement
  • 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 9 of 25
The proper test of a good fifth-wheel coupling is:
  • A Listen for a click
  • B Honk the horn
  • C Look at the locking jaws only
  • D Tug the trailer with the trailer parking brakes set
Correct answer: D
After coupling and locking, gently pull forward against the locked trailer brakes to confirm engagement.
Question 10 of 25
A tractor jackknife happens when:
  • A The fifth wheel disengages
  • B The tractor parking brake fails
  • C The drive wheels lose traction and the tractor begins to slide
  • D The trailer is too heavy
Correct answer: C
A drive-wheel skid causes the tractor to swing into the trailer at an angle.
Question 11 of 25
Which is true about combination braking?
  • A Brake balance is irrelevant
  • B ABS prevents jackknife in all cases
  • C Drive wheels never lock
  • D Trailer wheels lock more often than drive wheels in panic stops
Correct answer: D
Empty trailer wheels lock easily and contribute to jackknife and trailer-swing risks.
Question 12 of 25
A combination vehicle with empty trailers:
  • A Stops only with parking brake
  • B Stops faster than when loaded
  • C Stops in the same distance
  • D May actually take longer to stop because brakes are designed for the loaded weight
Correct answer: D
Empty trailers can lock up easily and skid, which counterintuitively increases stopping distance.
Question 13 of 25
When the trailer begins to skid, you should:
  • A Disconnect the air supply
  • B Apply the trailer hand valve harder
  • C Release the brakes to allow the trailer wheels to roll again, then steer
  • D Accelerate
Correct answer: C
Releasing the brakes lets the wheels rotate again so the trailer can recover its tracking.
Question 14 of 25
The "service" line on a tractor-trailer:
  • A Sends supply air to the trailer reservoirs
  • B Drains the trailer reservoir
  • C Carries electrical power
  • D Sends air pressure to apply trailer service brakes
Correct answer: D
The service line carries braking-pressure changes from the foot valve to the trailer brakes.
Question 15 of 25
If you are pulling two trailers, the heavier trailer should be:
  • A Last
  • B Loaded last
  • C First (closest to the tractor)
  • D Either position is fine
Correct answer: C
Heavier trailer first reduces the rear-trailer crack-the-whip effect.
Question 16 of 25
A combination vehicle has a higher rollover risk because:
  • A It uses air brakes
  • B Its tires are wider
  • C It is shorter than a straight truck
  • D Its center of gravity is high
Correct answer: D
Loaded trailers have high centers of gravity; rollover happens at speeds the driver thinks are safe.
Question 17 of 25
Glad hands are:
  • A Electrical connectors
  • B Coupling devices for connecting tractor air lines to the trailer
  • C Manual transmission shifters
  • D Brake adjustment levers
Correct answer: B
Glad hands have rubber seals and a metal coupler that joins the tractor and trailer air lines.
Question 18 of 25
Trailer parking brakes are released:
  • A By setting the red trailer-air-supply valve
  • B By pulling out the red trailer-air-supply valve
  • C By the trailer hand valve
  • D By pushing in the red trailer-air-supply valve
Correct answer: D
Pushing in the red knob charges the trailer brakes and releases the spring brakes.
Question 19 of 25
Trailer air supply valves on tractors are typically:
  • A Square, white, marked CHARGE
  • B Octagonal, red, marked TRAILER AIR SUPPLY
  • C Round, blue, marked TRACTOR
  • D Triangular, green, marked SERVICE
Correct answer: B
The trailer air-supply valve is the red, octagonal knob — a federal standard.
Question 20 of 25
After connecting the air lines, before pulling the tractor away, you must:
  • A Drain the wet tank
  • B Pump the brakes 10 times
  • C Drive away immediately
  • D Charge the trailer brakes by setting the trailer air supply control
Correct answer: D
After connecting, charge the trailer system and verify brake operation.
Question 21 of 25
When you make a wide right turn, you should:
  • A Use the shoulder
  • B Turn from the left lane
  • C 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
  • D Stop traffic by signaling left
Correct answer: C
Use only as much room as needed and keep the right side blocked to following vehicles.
Question 22 of 25
Before pulling the kingpin release lever to uncouple, you must:
  • A Lower the trailer landing gear and chock the trailer wheels
  • B Honk the horn
  • C Disconnect the electrical line first
  • D Drain the air tanks
Correct answer: A
Always lower the landing gear and chock the trailer so it cannot move once you pull out from under it.
Question 23 of 25
Combination vehicles are usually harder to drive than single CMVs because:
  • A They have a higher rollover risk
  • B They take more skill to back, couple, and uncouple
  • C They are heavier and longer
  • D All of the above
Correct answer: D
All three factors apply. The Combination Vehicles section of the federal manual emphasizes the higher skill needed.
Question 24 of 25
A skid is most likely to result in a jackknife if:
  • A The drive wheels lock and the trailer pushes the tractor sideways
  • B The trailer wheels lock briefly
  • C You are driving slowly
  • D The brakes are released gently
Correct answer: A
Drive-wheel lockup is the classic jackknife cause.
Question 25 of 25
After coupling, the locking jaws should:
  • A Be closed around the shank of the kingpin (not on the head)
  • B Be loose
  • C Be open
  • D Be missing
Correct answer: A
Visual check: jaws around the shank, not the head. A flashlight helps.

Study tips for the Colorado Combination Vehicles exam

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

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

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