Idaho Combination Vehicles CDL Practice Test
Below are 25 exam-style questions for the Idaho Combination Vehicles CDL knowledge test, modeled on the FMCSA-aligned content used by the Idaho Transportation Department 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.
- A Disconnect the electrical line first
- B Honk the horn
- C Lower the trailer landing gear and chock the trailer wheels
- D Drain the air tanks
- A The fuel mileage
- B The trailer following the same path as the tractor in a straight line
- C Lane positioning at intersections
- D Cargo placement
- A Lowered to the ground while driving
- B Fully raised before driving
- C Always halfway extended
- D Disconnected before driving
- A By pulling out the red trailer-air-supply valve
- B By the trailer hand valve
- C By pushing in the red trailer-air-supply valve
- D By setting the red trailer-air-supply valve
- A Small trailer movement
- B No effect
- C Loss of brake pressure
- D Large trailer angle changes; small inputs are key
- A It is illegal in some states
- B It is fine if you are careful
- C It is the standard procedure
- D It can damage the cab and the trailer (cab corner crush)
- A Swing wide to the right first to avoid hitting the curb
- B Keep the cab close to the curb and swing the front out so following cars cannot squeeze beside you on the right
- C Swing left then right
- D Stop in the middle of the turn
- A Stopping distances increase and the trailer can swing
- B Steering becomes easier
- C Stopping distances are normal
- D No effect on safety
- A Can be detected during pre-trip inspection by visual and pressure checks
- B Need a mechanic to find
- C Are caused by low fuel
- D Show up only at high speed
- A Set both tractor and trailer parking brakes
- B Use the trailer hand valve
- C Leave the engine running with the brakes off
- D Set only the tractor parking brake
- A Are normal until the lining is gone
- B Only need attention every 5 years
- C Make the truck quieter
- D Should be replaced when worn beyond manufacturer specs
- A Disconnect the air supply
- B Accelerate
- C Release the brakes to allow the trailer wheels to roll again, then steer
- D Apply the trailer hand valve harder
- 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
- A Release fifth wheel first, then connect lines
- B Lower landing gear, disconnect lines, release fifth wheel, pull tractor away
- C Pull tractor away first, then disconnect lines
- D No specific order is required
- A Reduced visibility along the trailer
- B Off-tracking on right turns
- C All of the above
- D Trailer sway in crosswinds
- A Last
- B Loaded last
- C Either position is fine
- D First (closest to the tractor)
- A Engine wear
- B Cargo placement
- C Driver fatigue
- D Air leakage in the supply line, low pressure, or a brake-balance issue
- A Back as fast as practical
- B Back without using mirrors
- C Back to the left whenever possible because you can see better
- D Always back to the right
- A All of the above
- B They take more skill to back, couple, and uncouple
- C They have a higher rollover risk
- D They are heavier and longer
- A Electrical power for trailer lights and ABS
- B Fuel
- C Air for the brakes
- D Hydraulic fluid
- A Use the shoulder
- B Stop traffic by signaling left
- C Turn from the left lane
- D 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
- A Pressing the pedal once at startup
- B Performing the seven-step air-brake check before each trip
- C Asking a mechanic
- D Listening to the brake light
- A Engine damage
- B Tire wear only
- C The trailer to come uncoupled
- D Rust on the cab
- A Pulling, sticking, or unusual feel as you apply the brakes
- B Engine knocking
- C Smoke from the cab
- D Steering wander only
- A All of the above
- B Backing too fast
- C Failure to grease
- D Coupling with the trailer too high
Study tips for the Idaho Combination Vehicles exam
The Combination Vehicles portion of the Idaho CDL exam is graded out of the bank of questions the Idaho Transportation Department 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 Idaho 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 Idaho 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 Idaho Transportation Department 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 Idaho 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 Idaho 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 Idaho Transportation Department Division of Motor Vehicles office.
Already comfortable with this endorsement? Drill another: ID General Knowledge · ID Air Brakes · ID Hazardous Materials · ID Passenger · ID School Bus · ID Tank Vehicle · ID Doubles / Triples
New to the CDL process in Idaho? Read How to apply for a CDL in Idaho for the document checklist and step-by-step timeline.