Iowa General Knowledge CDL Practice Test
Below are 25 exam-style questions for the Iowa General Knowledge CDL knowledge test, modeled on the FMCSA-aligned content used by the Iowa Department of Transportation. 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 Signal early, signal continuously, and cancel after the turn
- B Signal only at the moment you start turning
- C Use the four-way flashers instead of signals at intersections
- D Signal only when other vehicles are present
- A Engine oil level is safe to operate
- B Power steering fluid is at the proper level
- C Coolant level is above LOW and the cap is secure
- D All of the above
- A A traffic violation, but not a CDL disqualification
- B Allowed if the driver feels fine
- C Allowed off-duty only
- D Considered driving under the influence for CDL purposes
- A Brake hard immediately
- B Release the brake, let the wheels turn freely, and let the vehicle slow down
- C Steer sharply in the opposite direction
- D Accelerate
- A When you are stopped or moving slowly enough to be a hazard
- B Only on the highway
- C Whenever you feel like it
- D Only at night
- A Honk and proceed
- B Slow down, look, listen, and be prepared to stop
- C Always come to a full stop regardless of traffic
- D Cross at maximum speed to get over quickly
- A To save fuel and improve mileage
- B So the brake lights don't mislead following drivers and so the brakes don't overheat
- C To rest the right leg
- D To save brake pads and reduce drag
- A 0.04% or higher
- B 0.10% or higher
- C Any detectable amount above 0.00%
- D 0.08% or higher
- A Roads in direct sunlight
- B Gravel surfaces
- C Concrete pavement only
- D Bridges and overpasses
- A 20,000 lbs or more
- B 26,001 lbs or more
- C 10,001 lbs or more
- D 40,000 lbs or more
- A A reasonable time, before going off duty
- B 24 hours
- C 1 hour
- D 7 days
- A Drum brakes never need adjustment
- B Brakes self-adjust forever
- C Brake adjustment is the dispatcher's responsibility
- D Slack adjusters need periodic checking; pushrod travel beyond limits is out-of-service
- A It cools the brakes too much
- B It wastes brake pads
- C Brake fade can leave you with reduced or no braking power
- D It triggers the ABS warning light
- A Half the range of your low-beam headlights
- B Whatever speed feels safe
- C The full range of high-beam headlights when in use
- D The range of your low-beam headlights
- A All of the above
- B Trouble remembering the last few miles
- C Frequent yawning
- D Drifting in your lane
- A Drive faster to get out of the fog quickly
- B Use low-beam headlights and slow down
- C Use the four-ways while in motion at highway speed
- D Use high-beam headlights for maximum visibility
- A A warning
- B No federal consequence
- C A fine only
- D CDL disqualification for at least one year for a first offense
- A Three reflective triangles: 10 ft, 100 ft, and 200 ft toward approaching traffic
- B A spotter walking 1,000 ft up the road
- C A flare burning constantly
- D One reflective triangle within 10 feet
- A The area immediately next to it where other drivers are hidden in your blind spots
- B The fuel tank area
- C The area in front of the steer axle
- D A federal speed restriction
- A A vehicle is in safe operating condition
- B A trailer brake light is out
- C Required emergency equipment is missing
- D A passenger door is open
- A 2/32 inch
- B 6/32 inch
- C 4/32 inch
- D 1/32 inch
- A Powertrain wear and possible loss of control on slippery surfaces
- B Wasting fuel only
- C Engine damage
- D Annoying passengers
- A Only when the load is hazardous
- B At the end of the trip
- C Only if a warning light comes on
- D Within the first 25 miles, then about every 150 miles or every 3 hours
- A Gross Cargo Weight Rating
- B Gross Combination Weight Rating
- C Government Combination Weight Reading
- D General Carrier Weight Rating
- A Coast in neutral
- B Look for an escape ramp
- C Use the parking brake hard
- D Shift into reverse
Study tips for the Iowa General Knowledge exam
The General Knowledge portion of the Iowa CDL exam is graded out of the bank of questions the Iowa Department of Transportation draws from each year. While the exact bank is not published, every question is sourced from the General Knowledge chapter of the Iowa 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 Iowa 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 General Knowledge.
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 Iowa Department of Transportation 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 General Knowledge 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 Iowa General Knowledge practice test before scheduling the real exam.
Next steps
Missed more than four questions? Re-read the General Knowledge study guide and the matching chapter in the official Iowa 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 Iowa Department of Transportation office.
Already comfortable with this endorsement? Drill another: IA Air Brakes · IA Combination Vehicles · IA Hazardous Materials · IA Passenger · IA School Bus · IA Tank Vehicle · IA Doubles / Triples
New to the CDL process in Iowa? Read How to apply for a CDL in Iowa for the document checklist and step-by-step timeline.