District of Columbia Combination Vehicles CDL Practice Test
Below are 25 exam-style questions for the District of Columbia Combination Vehicles CDL knowledge test, modeled on the FMCSA-aligned content used by the DC Department 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 Brake fade
- B Wheel damage
- C Off-tracking — the trailer wheels follow a tighter arc than the tractor
- D No off-tracking
- A Listening to the brake light
- B Asking a mechanic
- C Pressing the pedal once at startup
- D Performing the seven-step air-brake check before each trip
- A Stop traffic by signaling left
- B Use the shoulder
- 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 Turn from the left lane
- A Carries electrical power
- B Sends air pressure to apply trailer service brakes
- C Sends supply air to the trailer reservoirs
- D Drains the trailer reservoir
- A Stop on the tracks if traffic ahead slows
- B Cross in a low gear without shifting
- C Shift in the middle of the track
- D Honk and accelerate
- A Coupling with the trailer too high
- B Failure to grease
- C Backing too fast
- D All of the above
- A Always halfway extended
- B Fully raised before driving
- C Disconnected before driving
- D Lowered to the ground while driving
- A Pull tractor away first, then disconnect lines
- B Release fifth wheel first, then connect lines
- C Lower landing gear, disconnect lines, release fifth wheel, pull tractor away
- D No specific order is required
- A A wheel bearing fails
- B The tractor brakes lock up
- C The fifth wheel breaks
- D The trailer brakes lock up
- A Connect any line first; order doesn't matter
- B Connect only air; electrical is optional
- C Connect air emergency line first, then service line, then electrical (or per company policy) — verify with brake check
- D Connect electrical first, then air
- A Stop in the middle of the turn
- B Swing wide to the right first to avoid hitting the curb
- C Keep the cab close to the curb and swing the front out so following cars cannot squeeze beside you on the right
- D Swing left then right
- A Only at the destination
- B Every 3 hours
- C Only at the start of the day
- D Before, during, and after coupling
- A Tire wear only
- B Rust on the cab
- C The trailer to come uncoupled
- D Engine damage
- A Fuel
- B Hydraulic fluid
- C Air for the brakes
- D Electrical power for trailer lights and ABS
- A Need a mechanic to find
- B Are caused by low fuel
- C Can be detected during pre-trip inspection by visual and pressure checks
- D Show up only at high speed
- A Leave the gear up
- B Lower the landing gear all the way until firmly on the ground, then a few extra cranks
- C Raise the gear partway
- D Use blocks instead
- A The drive wheels lock and the trailer pushes the tractor sideways
- B You are driving slowly
- C The trailer wheels lock briefly
- D The brakes are released gently
- A Steering becomes easier
- B Stopping distances increase and the trailer can swing
- C No effect on safety
- D Stopping distances are normal
- A Trailer wheels lock more often than drive wheels in panic stops
- B Drive wheels never lock
- C ABS prevents jackknife in all cases
- D Brake balance is irrelevant
- A Set only the tractor parking brake
- B Use the trailer hand valve
- C Set both tractor and trailer parking brakes
- D Leave the engine running with the brakes off
- A Maximum legal height
- B Whatever height it happens to be
- 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
- A Sliding sideways
- B The trailer wheels follow a tighter arc than the tractor wheels in a turn
- C Loss of traction
- D Driving off the road
- A Be removed
- B Be locked at half-height
- C Be in the low position when traveling
- D Be in the stowed (high) position when traveling
- A Driver fatigue
- B Cargo placement
- C Engine wear
- D Air leakage in the supply line, low pressure, or a brake-balance issue
- A Cargo placement
- B The fuel mileage
- C The trailer following the same path as the tractor in a straight line
- D Lane positioning at intersections
Study tips for the District of Columbia Combination Vehicles exam
The Combination Vehicles portion of the District of Columbia CDL exam is graded out of the bank of questions the DC Department 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 District of Columbia 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 District of Columbia 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 DC Department 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 District of Columbia 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 District of Columbia 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 DC Department of Motor Vehicles office.
Already comfortable with this endorsement? Drill another: DC General Knowledge · DC Air Brakes · DC Hazardous Materials · DC Passenger · DC School Bus · DC Tank Vehicle · DC Doubles / Triples
New to the CDL process in District of Columbia? Read How to apply for a CDL in District of Columbia for the document checklist and step-by-step timeline.