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Mississippi Combination Vehicles CDL Practice Test

Below are 25 exam-style questions for the Mississippi Combination Vehicles CDL knowledge test, modeled on the FMCSA-aligned content used by the Mississippi 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
A worn or damaged fifth wheel can cause:
  • A Rust on the cab
  • B The trailer to come uncoupled
  • C Engine damage
  • D Tire wear only
Correct answer: B
Worn locking jaws or a cracked structure can fail and release the trailer in motion.
Question 2 of 25
Trailer ABS uses:
  • A A separate compressor
  • B Sensors at each wheel that release brake pressure when wheel lockup is detected
  • C Hydraulic brakes
  • D Hand valves
Correct answer: B
Wheel-speed sensors trigger valves to release pressure when lockup is detected.
Question 3 of 25
A safe combination-vehicle following distance is at least:
  • A Two car lengths
  • B A vehicle length
  • C One second per 10 feet of vehicle length below 40 mph, plus one extra second above 40 mph
  • D No specific rule
Correct answer: C
A 60-ft combination needs at least 6 seconds under 40 mph, 7 seconds above 40 mph.
Question 4 of 25
The fifth-wheel locking lever should be:
  • A Released and visible after coupling
  • B Tied with rope
  • C Removed before driving
  • D Locked and the safety latch in place after coupling
Correct answer: D
After backing under, the locking jaws must close around the kingpin and the safety latch must be in place.
Question 5 of 25
Which of the following can damage a fifth wheel?
  • A Backing too fast
  • B Failure to grease
  • C Coupling with the trailer too high
  • D All of the above
Correct answer: D
All three: high trailer skips the jaws, fast backing impacts hardware, and lack of lubrication accelerates wear.
Question 6 of 25
The trailer landing gear (dolly legs) should be:
  • A Always halfway extended
  • B Disconnected before driving
  • C Lowered to the ground while 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 7 of 25
A combination vehicle has a higher rollover risk because:
  • A Its tires are wider
  • B It is shorter than a straight truck
  • C It uses air brakes
  • 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 8 of 25
During a brake check before moving, you should look for:
  • A Steering wander only
  • B Smoke from the cab
  • C Pulling, sticking, or unusual feel as you apply the brakes
  • D Engine knocking
Correct answer: C
Low-speed brake test identifies pulling, sticking, or weakness so you don't discover it on the highway.
Question 9 of 25
Trailer wheels with worn brake linings:
  • A Are normal until the lining is gone
  • B Should be replaced when worn beyond manufacturer specs
  • C Only need attention every 5 years
  • D Make the truck quieter
Correct answer: B
Worn linings are an out-of-service item; replace per manufacturer/federal limits.
Question 10 of 25
A tractor jackknife happens when:
  • A The trailer is too heavy
  • B The drive wheels lose traction and the tractor begins to slide
  • C The tractor parking brake fails
  • D The fifth wheel disengages
Correct answer: B
A drive-wheel skid causes the tractor to swing into the trailer at an angle.
Question 11 of 25
When the trailer brakes are operating but pulling weakly, this can indicate:
  • A Cargo placement
  • B Driver fatigue
  • C Air leakage in the supply line, low pressure, or a brake-balance issue
  • D Engine wear
Correct answer: C
Weak trailer brakes are usually an air-system problem and require diagnosis before continuing.
Question 12 of 25
The trailer hand valve should NOT be used to:
  • A Both for parking and to prevent jackknife
  • B Hold the vehicle when parking
  • C Apply trailer brakes momentarily
  • D Test the trailer brakes
Correct answer: A
Don't use it to park (it can leak off) or to prevent a jackknife (it locks the trailer wheels and worsens the skid).
Question 13 of 25
If you cross the air lines (service to emergency and vice versa) when coupling:
  • A Nothing will happen
  • B The horn will sound
  • C You will notice immediately because trailer brakes will not work properly
  • D The trailer brakes will be locked on
Correct answer: C
Crossed glad hands often produce no air flow to brake chambers and incorrect brake operation; you should notice on the brake test.
Question 14 of 25
The seven-pin connector on a tractor-trailer carries:
  • A Fuel
  • B Air for the brakes
  • C Hydraulic fluid
  • 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 15 of 25
You should inspect a combination vehicle for:
  • A Loose or missing fifth-wheel mounting bolts
  • B All of the above
  • C Cracks in the kingpin
  • D Misalignment between tractor and trailer
Correct answer: B
All three are pre-trip combination-vehicle items.
Question 16 of 25
Which is true about combination braking?
  • A Trailer wheels lock more often than drive wheels in panic stops
  • B ABS prevents jackknife in all cases
  • C Brake balance is irrelevant
  • D Drive wheels never lock
Correct answer: A
Empty trailer wheels lock easily and contribute to jackknife and trailer-swing risks.
Question 17 of 25
Tracking refers to:
  • A Cargo placement
  • B The fuel mileage
  • C Lane positioning at intersections
  • 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 18 of 25
When parking a tractor-trailer, you should:
  • A Use the trailer hand valve
  • B Set only the tractor parking brake
  • C Set both tractor and trailer parking brakes
  • D Leave the engine running with the brakes off
Correct answer: C
For full parking, both parking brakes apply.
Question 19 of 25
The "emergency" line (supply line) on a tractor-trailer:
  • A Sends supply air to the trailer reservoirs and controls the trailer emergency brakes
  • B Operates the parking brake only
  • C Drains the wet tank
  • D Carries electrical signals
Correct answer: A
Loss of pressure on the emergency line causes the trailer's emergency brake to apply automatically.
Question 20 of 25
Brake-system pressure should be checked:
  • A Only at the start of the day
  • B Only at the destination
  • C Every 3 hours
  • D Before, during, and after coupling
Correct answer: D
Pressure changes during coupling indicate connection problems early.
Question 21 of 25
Most tire problems on a combination vehicle:
  • A Are caused by low fuel
  • B Show up only at high speed
  • C Can be detected during pre-trip inspection by visual and pressure checks
  • D Need a mechanic to find
Correct answer: C
Visual and pressure checks catch most problems before they become roadside failures.
Question 22 of 25
The proper test of a good fifth-wheel coupling is:
  • A Tug the trailer with the trailer parking brakes set
  • B Listen for a click
  • C Honk the horn
  • D Look at the locking jaws only
Correct answer: A
After coupling and locking, gently pull forward against the locked trailer brakes to confirm engagement.
Question 23 of 25
A "trailer skid" usually starts because:
  • A The trailer brakes lock up
  • B A wheel bearing fails
  • C The tractor brakes lock up
  • D The fifth wheel breaks
Correct answer: A
Locking the trailer brakes is the most common cause of a trailer skid (jackknife).
Question 24 of 25
The crank handle on the landing gear should:
  • A Be in the low position when traveling
  • B Be locked at half-height
  • C Be in the stowed (high) position when traveling
  • D Be removed
Correct answer: C
Stow the crank up so it doesn't catch on something while traveling.
Question 25 of 25
When backing a trailer, small steering inputs cause:
  • A Loss of brake pressure
  • B No effect
  • C Small trailer movement
  • D Large trailer angle changes; small inputs are key
Correct answer: D
Trailer responds aggressively to small wheel inputs in reverse — back slowly and correct quickly.

Study tips for the Mississippi Combination Vehicles exam

The Combination Vehicles portion of the Mississippi CDL exam is graded out of the bank of questions the Mississippi 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 Mississippi 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 Mississippi 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 Mississippi 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 Mississippi 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 Mississippi 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 Mississippi Department of Public Safety office.

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

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