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Delaware Combination Vehicles CDL Practice Test

Below are 25 exam-style questions for the Delaware Combination Vehicles CDL knowledge test, modeled on the FMCSA-aligned content used by the Delaware 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
When you uncouple a trailer with cargo on it, you should:
  • A Leave the gear up
  • B Use blocks instead
  • C Raise the gear partway
  • D Lower the landing gear all the way until firmly on the ground, then a few extra cranks
Correct answer: D
Make sure the gear takes the full weight before pulling out from under.
Question 2 of 25
Most tire problems on a combination vehicle:
  • A Show up only at high speed
  • B Need a mechanic to find
  • C Are caused by low fuel
  • D Can be detected during pre-trip inspection by visual and pressure checks
Correct answer: D
Visual and pressure checks catch most problems before they become roadside failures.
Question 3 of 25
A "trailer skid" usually starts because:
  • A The fifth wheel breaks
  • B A wheel bearing fails
  • C The trailer brakes lock up
  • D The tractor brakes lock up
Correct answer: C
Locking the trailer brakes is the most common cause of a trailer skid (jackknife).
Question 4 of 25
When uncoupling, after the tractor is clear, you should:
  • A Disable the trailer parking brake
  • B Connect the lines back to the tractor
  • 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 5 of 25
After coupling, the locking jaws should:
  • A Be loose
  • B Be closed around the shank of the kingpin (not on the head)
  • C Be open
  • D Be missing
Correct answer: B
Visual check: jaws around the shank, not the head. A flashlight helps.
Question 6 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 Worn out tires
  • D Cargo movement
Correct answer: A
Speed and following distance dominate the causes. Increase cushion and slow down.
Question 7 of 25
Glad hands are:
  • A Manual transmission shifters
  • B Coupling devices for connecting tractor air lines to the trailer
  • C Electrical connectors
  • 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 8 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 Stop traffic by signaling left
  • C Use the shoulder
  • D Turn from the left lane
Correct answer: A
Use only as much room as needed and keep the right side blocked to following vehicles.
Question 9 of 25
A safe combination-vehicle following distance is at least:
  • A Two car lengths
  • B No specific rule
  • C A vehicle length
  • D One second per 10 feet of vehicle length below 40 mph, plus one extra second above 40 mph
Correct answer: D
A 60-ft combination needs at least 6 seconds under 40 mph, 7 seconds above 40 mph.
Question 10 of 25
The "emergency" line (supply line) on a tractor-trailer:
  • A Carries electrical signals
  • B Operates the parking brake only
  • C Sends supply air to the trailer reservoirs and controls the trailer emergency brakes
  • D Drains the wet tank
Correct answer: C
Loss of pressure on the emergency line causes the trailer's emergency brake to apply automatically.
Question 11 of 25
When you drive a combination vehicle, watch for:
  • A Reduced visibility along the trailer
  • B All of the above
  • C Off-tracking on right turns
  • D Trailer sway in crosswinds
Correct answer: B
All three are routine combination-vehicle considerations.
Question 12 of 25
A combination vehicle has a higher rollover risk because:
  • A Its center of gravity is high
  • B Its tires are wider
  • C It is shorter than a straight truck
  • D It uses air brakes
Correct answer: A
Loaded trailers have high centers of gravity; rollover happens at speeds the driver thinks are safe.
Question 13 of 25
The "service" line on a tractor-trailer:
  • A Sends supply air to the trailer reservoirs
  • B Sends air pressure to apply trailer service brakes
  • C Carries electrical power
  • D Drains the trailer reservoir
Correct answer: B
The service line carries braking-pressure changes from the foot valve to the trailer brakes.
Question 14 of 25
When parking a tractor-trailer, you should:
  • A Set both tractor and trailer parking brakes
  • B Use the trailer hand valve
  • C Set only the tractor parking brake
  • D Leave the engine running with the brakes off
Correct answer: A
For full parking, both parking brakes apply.
Question 15 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 brakes are released gently
  • C You are driving slowly
  • D The trailer wheels lock briefly
Correct answer: A
Drive-wheel lockup is the classic jackknife cause.
Question 16 of 25
Trailer parking brakes are released:
  • A By pushing in the red trailer-air-supply valve
  • B By the trailer hand valve
  • C By setting the red trailer-air-supply valve
  • D By pulling out the red trailer-air-supply valve
Correct answer: A
Pushing in the red knob charges the trailer brakes and releases the spring brakes.
Question 17 of 25
Brake-system pressure should be checked:
  • A Before, during, and after coupling
  • B Only at the destination
  • C Only at the start of the day
  • D Every 3 hours
Correct answer: A
Pressure changes during coupling indicate connection problems early.
Question 18 of 25
A converter dolly:
  • A Is part of the tractor
  • B Replaces the fifth wheel on the tractor
  • C Is used only when triple-towing
  • 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 19 of 25
The proper test of a good fifth-wheel coupling is:
  • A Look at the locking jaws only
  • B Tug the trailer with the trailer parking brakes set
  • C Honk the horn
  • D Listen for a click
Correct answer: B
After coupling and locking, gently pull forward against the locked trailer brakes to confirm engagement.
Question 20 of 25
Off-tracking means:
  • A Loss of traction
  • B Driving off the road
  • C Sliding sideways
  • D The trailer wheels follow a tighter arc than the tractor wheels in a turn
Correct answer: D
In a right turn, the trailer wheels cut the corner. To compensate, the tractor must swing wider.
Question 21 of 25
When a tractor pulls a trailer with brakes that are out of balance:
  • A No effect on safety
  • B Stopping distances are normal
  • C Steering becomes easier
  • 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 22 of 25
When the trailer brakes are operating but pulling weakly, this can indicate:
  • A Engine wear
  • B Driver fatigue
  • C Air leakage in the supply line, low pressure, or a brake-balance issue
  • D Cargo placement
Correct answer: C
Weak trailer brakes are usually an air-system problem and require diagnosis before continuing.
Question 23 of 25
If you are pulling two trailers, the heavier trailer should be:
  • A Last
  • B First (closest to the tractor)
  • C Loaded last
  • D Either position is fine
Correct answer: B
Heavier trailer first reduces the rear-trailer crack-the-whip effect.
Question 24 of 25
You should never back under a trailer that is:
  • A Too high — it can damage the kingpin or skip over the fifth wheel
  • B Properly chocked
  • C Empty
  • D Loaded
Correct answer: A
A trailer set too high can skip over the fifth-wheel jaws and not lock, or damage the coupling.
Question 25 of 25
You should inspect a combination vehicle for:
  • A Cracks in the kingpin
  • B All of the above
  • C Misalignment between tractor and trailer
  • D Loose or missing fifth-wheel mounting bolts
Correct answer: B
All three are pre-trip combination-vehicle items.

Study tips for the Delaware Combination Vehicles exam

The Combination Vehicles portion of the Delaware CDL exam is graded out of the bank of questions the Delaware 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 Delaware 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 Delaware 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 Delaware 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 Delaware 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 Delaware 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 Delaware Division of Motor Vehicles office.

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

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