Iowa General Knowledge CDL Practice Test
25 realistic General Knowledge practice questions for Iowa CDL applicants. Required for: All CDL applicants (Class A, B, and C). Official test: 50 questions, 40 correct to pass.
Question 1 of 25 · Speed Management
Whenever you double your speed, the impact in a crash is:
-
A.
Doubled
-
B.
The same
-
C.
Four times greater
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D.
Half
Correct answer: C.
Crash energy increases with the square of speed — doubling speed quadruples crash forces.
Question 2 of 25 · Inspection
What is the minimum tread depth for non-steering axle tires?
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A.
1/32 inch
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B.
2/32 inch
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C.
4/32 inch
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D.
6/32 inch
Correct answer: B.
Federal regulations require at least 2/32 inch on non-steering tires.
Question 3 of 25 · Inspection
What is the minimum tread depth for steering axle tires?
-
A.
2/32 inch
-
B.
4/32 inch
-
C.
6/32 inch
-
D.
8/32 inch
Correct answer: B.
Federal regulations require at least 4/32 inch tread depth on steering axle tires.
Question 4 of 25 · Mountain Driving
What may happen if you don't shift gears properly when going up a hill?
-
A.
You will use less fuel
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B.
The transmission will be damaged
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C.
You may lose control on a downgrade
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D.
Engine RPM will be too low
Correct answer: C.
Improper gear use can result in losing control of speed, especially on the way back down a hill.
Question 5 of 25 · Night Driving
Which of these is true about driving at night?
-
A.
You can see further than during the day
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B.
Your reaction time is faster at night
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C.
You should reduce your speed
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D.
High beams should always be used
Correct answer: C.
You see less and farther obstacles appear later at night. Slow down so you can stop within the area lit by your headlights.
Question 6 of 25 · Inspection
Mirror adjustment should be checked:
-
A.
Only at the start of the trip
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B.
Only when something seems wrong
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C.
Prior to the start of any trip and can only be checked accurately when the trailer(s) are straight
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D.
Once per week
Correct answer: C.
Adjust and check mirrors before each trip while the trailers are straight.
Question 7 of 25 · Inspection
Excessive heat in tires can:
-
A.
Improve handling
-
B.
Cause tire failure
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C.
Help fuel economy
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D.
Increase tire life
Correct answer: B.
Excessive heat causes blowouts and serious damage. Check for hot tires after driving.
Question 8 of 25 · Adverse Conditions
Hydroplaning is most likely to occur when:
-
A.
Tires are properly inflated
-
B.
Speed is below 30 mph
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C.
Roads are dry
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D.
Tires lose contact with the road on wet pavement
Correct answer: D.
Hydroplaning happens when water builds up between the tire and the road, causing loss of contact.
Question 9 of 25 · Rail Crossings
When approaching a railroad crossing without flashing lights or gates, you should:
-
A.
Slow down, look, and listen for trains
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B.
Always come to a complete stop
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C.
Speed up to clear the crossing quickly
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D.
Sound horn but maintain speed
Correct answer: A.
Without active warning devices, slow down and look and listen carefully for an approaching train.
Question 10 of 25 · CDL Rules
Driving with a BAC of 0.04 or higher in a CMV will result in:
-
A.
A warning
-
B.
A 30-day suspension
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C.
A CDL disqualification of at least one year
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D.
No penalty if off-duty
Correct answer: C.
A first offense disqualifies you for at least one year (three years if hauling hazardous materials).
Question 11 of 25 · Night Driving
You should use low beam headlights:
-
A.
Whenever you can
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B.
Within 500 feet of an oncoming vehicle and 500 feet behind another vehicle
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C.
Only in fog
-
D.
On lighted city streets only
Correct answer: B.
Use low beams within 500 feet of oncoming traffic and when following within 500 feet of another vehicle.
Question 12 of 25 · CDL Rules
What is the legal blood alcohol concentration (BAC) limit for CDL drivers?
-
A.
0.08%
-
B.
0.05%
-
C.
0.04%
-
D.
0.02%
Correct answer: C.
Federal CDL law sets the BAC limit at 0.04%, half the limit for non-commercial drivers.
Question 13 of 25 · Driver Wellness
Aggressive drivers should be:
-
A.
Confronted
-
B.
Reported and given plenty of room
-
C.
Followed closely
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D.
Passed quickly without signaling
Correct answer: B.
Stay clear of aggressive drivers and report dangerous behavior to authorities.
Question 14 of 25 · Communication
Drivers should signal their intentions at least:
-
A.
Right at the moment of turning
-
B.
50 feet before the turn
-
C.
100 feet before the turn
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D.
In the city, no signaling needed
Correct answer: C.
Signal at least 100 feet before turning to give following drivers time to react.
Question 15 of 25 · CDL Rules
Refusing a chemical test for alcohol or drugs while operating a CMV will result in:
-
A.
A warning
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B.
A 90-day suspension
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C.
CDL disqualification of at least one year
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D.
A simple fine
Correct answer: C.
Refusal is treated the same as testing positive — minimum one-year disqualification.
Question 16 of 25 · Emergency Equipment
What three kinds of emergency equipment must you have in your vehicle?
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A.
Spare tire, fuses, and reflective triangles
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B.
Fire extinguisher, spare fuses (if equipped), and warning devices
-
C.
First aid kit, water, and flares
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D.
Tool kit, fuel can, and flag
Correct answer: B.
You must have a fire extinguisher, spare electrical fuses (if equipped), and warning devices for stopped vehicles.
Question 17 of 25 · Cargo
Which is true about cargo securement?
-
A.
Drivers are responsible for inspecting cargo
-
B.
Cargo only needs to be inspected at the start of a trip
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C.
Securement is the shipper's sole responsibility
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D.
Once strapped, cargo never needs re-checking
Correct answer: A.
Drivers must inspect cargo and its securement at the start of the trip and re-check periodically.
Question 18 of 25 · Communication
When changing lanes you should:
-
A.
Do it quickly so other drivers don't catch up
-
B.
Signal early and check mirrors before and during the lane change
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C.
Turn off the radio
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D.
Speed up first
Correct answer: B.
Signal early, check mirrors, and look for traffic before and during the change.
Question 19 of 25 · Driver Wellness
Which of the following affects alcohol absorption into the body?
-
A.
Drinking on a full stomach
-
B.
How fast you drink
-
C.
Body weight
-
D.
All of the above
Correct answer: D.
Stomach contents, drinking speed, and body weight all influence absorption.
Question 20 of 25 · Speed Management
Engine brakes (Jakes) should not be used:
-
A.
On dry pavement at highway speed
-
B.
On slippery roads while loaded or empty
-
C.
When descending a steep grade
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D.
Heading toward a long downhill
Correct answer: B.
Avoid engine brakes on slippery roads — they can cause the drive wheels to lose traction.
Question 21 of 25 · Driver Wellness
Distracted driving includes:
-
A.
Talking on a hand-held cell phone
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B.
Eating
-
C.
Reading maps
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D.
All of the above
Correct answer: D.
All of these activities take attention from driving and are forms of distracted driving.
Question 22 of 25 · Inspection
What is the most important reason for doing a vehicle inspection?
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A.
To meet DOT requirements
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B.
Safety for yourself and others
-
C.
To save fuel
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D.
To avoid roadside inspections
Correct answer: B.
Safety is the most important reason. A defective vehicle puts you, your cargo, and others at risk.
Question 23 of 25 · Testing
The road test will be scored on:
-
A.
How fast you complete the route
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B.
Vehicle inspection, basic control, and on-road driving
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C.
Whether you wear a uniform
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D.
Your appearance
Correct answer: B.
You'll be evaluated on inspection skills, basic control skills, and safe on-road driving performance.
Question 24 of 25 · Emergency Equipment
When stopped on the side of a level, straight, two-lane road, where should the three reflective triangles be placed?
-
A.
10, 50, and 100 feet behind the vehicle
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B.
10, 100, and 200 feet behind the vehicle
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C.
On the front, side, and rear of the vehicle
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D.
50, 100, and 200 feet on the traffic side
Correct answer: B.
Triangles go 10, 100, and 200 feet behind the vehicle on a straight, level, two-lane road.
Question 25 of 25 · Testing
When taking the road test, you will be expected to:
-
A.
Demonstrate the basic control skills only
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B.
Drive only on the highway
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C.
Show that you can perform safely in normal traffic
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D.
Drive only in residential areas
Correct answer: C.
The road test evaluates safe performance in actual traffic conditions.
About the General Knowledge Test
The General Knowledge test covers safe vehicle inspection, basic vehicle control, shifting gears, communicating, controlling speed, controlling distance, seeing hazards, distracted driving, aggressive drivers, communicating with other drivers, night driving, driving in fog, winter driving, hot weather driving, mountain driving, driving emergencies, anti-lock braking systems, skid recovery, accident procedures, fires, alcohol and other drugs, hazardous materials awareness, and staying alert and fit to drive. Every commercial driver in the United States must pass this test before any other CDL endorsement can be added.
The Iowa Department of Transportation — Motor Vehicle Division administers this knowledge test as part of its commercial driver license program. To earn the CDL General Knowledge on your Iowa CDL, you need to score at least 40 out of 50 on the official version.
Topics covered on this practice test
- Inspection: 5 questions
- CDL Rules: 3 questions
- Driver Wellness: 3 questions
- Speed Management: 2 questions
- Night Driving: 2 questions
- Communication: 2 questions
- Emergency Equipment: 2 questions
- Testing: 2 questions
- Mountain Driving: 1 question
- Adverse Conditions: 1 question
- Rail Crossings: 1 question
- Cargo: 1 question
How to use this practice test
- Read each question carefully. CDL questions are written precisely — small wording differences matter.
- Click "Show Answers & Explanations" only after answering every question. Don't peek mid-test.
- Read the explanation for every question, even ones you got right. The reasoning is more important than the answer.
- Repeat the test until you score 100%. The questions are deterministic per state, so you can track your improvement over multiple sessions.
- Move on to the other endorsement tests for Iowa until you're ready for the official exam.
Tips specific to the General Knowledge test
The General Knowledge test is the foundation of every CDL. Topics include vehicle inspection, basic control, shifting, communicating, controlling speed, controlling space, hazard perception, distracted driving, night driving, fog, winter, hot weather, mountain driving, emergencies, anti-lock brakes, skid recovery, accident procedures, fires, alcohol, hazardous materials awareness, and staying alert. Most failures come from speeding through inspection-related questions; slow down and read carefully.
Other practice tests for Iowa