Illinois General Knowledge CDL Practice Test
25 realistic General Knowledge practice questions for Illinois CDL applicants. Required for: All CDL applicants (Class A, B, and C). Official test: 50 questions, 40 correct to pass.
Question 1 of 25 · Backing
You should always try to park:
-
A.
So that you will have to back when leaving
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B.
So that you can pull forward when leaving
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C.
On the right shoulder of any highway
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D.
Without using the parking brake
Correct answer: B.
Park so that you can pull forward to leave. Backing should always be avoided when possible.
Question 2 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 3 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
-
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 4 of 25 · Backing
The most important hand signal you and a helper should agree on is:
-
A.
Speed up
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B.
Stop
-
C.
Turn left
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D.
Back straight
Correct answer: B.
Always agree on a clear stop signal before backing. The helper must be able to stop you instantly.
Question 5 of 25 · Speed Management
Engine retarders should be turned off when:
-
A.
Driving uphill
-
B.
The road is wet, icy, or snow covered
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C.
Traffic is heavy
-
D.
You are loaded
Correct answer: B.
Retarders can cause drive wheels to skid on slippery surfaces. Turn them off in poor traction conditions.
Question 6 of 25 · Driver Wellness
You should not eat or drink while driving because:
-
A.
It is illegal in all states
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B.
Spills can distract you
-
C.
You should not put both hands on the wheel
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D.
It might damage the vehicle
Correct answer: B.
Eating and drinking divert attention and create spill hazards.
Question 7 of 25 · Emergency Maneuvers
Controlled braking is:
-
A.
Pressing the brake to the floor and holding
-
B.
Applying brakes hard enough to lock the wheels
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C.
Applying brakes to keep wheels just short of locking
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D.
Releasing brakes and coasting
Correct answer: C.
Controlled braking applies the brake firmly without locking the wheels, keeping the steering straight.
Question 8 of 25 · Adverse Conditions
What should you do before driving in fog?
-
A.
Use high beams to see further
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B.
Slow down and use low beams and fog lights if equipped
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C.
Speed up to clear the fog area
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D.
Follow another vehicle closely
Correct answer: B.
Slow down before entering fog. Use low beams and any installed fog lights.
Question 9 of 25 · Inspection
When checking the engine compartment, your vehicle should be:
-
A.
Idling in neutral
-
B.
On a slight incline
-
C.
Parked on level ground with the parking brake set and wheels chocked
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D.
Running with the parking brake off
Correct answer: C.
Always inspect the engine compartment with the vehicle parked on level ground, parking brake set, and wheels chocked.
Question 10 of 25 · Communication
When should you check your mirrors?
-
A.
Only before changing lanes
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B.
Frequently, to know what is around your vehicle
-
C.
When parking only
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D.
Only at intersections
Correct answer: B.
Check mirrors regularly to know what is happening around your vehicle.
Question 11 of 25 · Inspection
What is the minimum tread depth for non-steering axle tires?
-
A.
1/32 inch
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B.
2/32 inch
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C.
4/32 inch
-
D.
6/32 inch
Correct answer: B.
Federal regulations require at least 2/32 inch on non-steering tires.
Question 12 of 25 · Inspection
What is the most important reason for doing a vehicle inspection?
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A.
To meet DOT requirements
-
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 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 · Cargo
Which is correct about cargo and weight balance?
-
A.
Heavy cargo should always be at the rear
-
B.
Cargo should be balanced and secured to prevent shifting
-
C.
Side-to-side balance does not matter
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D.
Top-heavy loads improve stability
Correct answer: B.
Cargo must be evenly balanced and well secured. Top-heavy loads increase rollover risk.
Question 15 of 25 · Basic Control
Where should the wheel chocks be placed?
-
A.
Behind one tire
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B.
In front of and behind tires on the same axle
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C.
Only when on a hill
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D.
Both front and rear tires of the steer axle
Correct answer: B.
Place chocks both in front of and behind the wheels to prevent the vehicle from rolling either way.
Question 16 of 25 · Backing
Which of these statements about backing a heavy vehicle is true?
-
A.
Back in a curved path whenever possible
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B.
Avoid backing whenever you can
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C.
Back as quickly as possible
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D.
Use only the right mirror
Correct answer: B.
Avoid backing whenever you can. Park where you will be able to pull forward to leave.
Question 17 of 25 · Vehicle Dynamics
Empty trucks:
-
A.
Always stop more quickly than loaded trucks
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B.
Have less traction because there is less weight on the drive axles
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C.
Can take curves at higher speeds safely
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D.
Are not affected by wind
Correct answer: B.
Empty trucks have reduced traction on drive axles and require greater stopping distances than loaded trucks.
Question 18 of 25 · Communication
Communicating your intentions means:
-
A.
Honking before each turn
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B.
Using turn signals, brake lights, and the horn appropriately
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C.
Flashing high beams at all drivers
-
D.
Hand signals only at intersections
Correct answer: B.
Use signals, brake lights, and the horn properly to communicate. Hand signals supplement them.
Question 19 of 25 · Emergency Maneuvers
Which of the following is a sign of tire failure?
-
A.
A loud "bang" sound
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B.
Vibration or thumping
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C.
Heavy steering or fishtailing
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D.
All of the above
Correct answer: D.
A bang, vibration, heavy steering, or fishtailing can all indicate tire failure.
Question 20 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 21 of 25 · Driver Wellness
Which of the following is NOT a sign of fatigued driving?
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A.
Frequent yawning
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B.
Drifting from your lane
-
C.
Rapid blinking and clear focus
-
D.
Missing exits or traffic signs
Correct answer: C.
Rapid blinking with clear focus is not a fatigue sign. Yawning, drifting, and missing exits all are.
Question 22 of 25 · Speed Management
When you double your speed, your stopping distance is multiplied by approximately:
-
A.
Two
-
B.
Three
-
C.
Four
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D.
Six
Correct answer: C.
Stopping distance grows with the square of speed. Doubling speed roughly quadruples the distance needed to stop.
Question 23 of 25 · Adverse Conditions
Hydroplaning is most likely to occur when:
-
A.
Tires are properly inflated
-
B.
Speed is below 30 mph
-
C.
Roads are dry
-
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 24 of 25 · Speed Management
You are driving a vehicle that could safely be driven at 55 mph on an open highway. The traffic is heavy and moving at 35 mph. The safest speed for your vehicle in this traffic is most likely:
-
A.
25 mph
-
B.
35 mph
-
C.
45 mph
-
D.
55 mph
Correct answer: B.
You should generally adjust to the speed of surrounding traffic when it is safe to do so.
Question 25 of 25 · Inspection
Pre-trip inspection of the vehicle should be done in the same order each time so that you:
-
A.
Will look professional to other drivers
-
B.
Will learn it well and not skip anything
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C.
Can finish faster
-
D.
Pass the test more easily
Correct answer: B.
Following the same order helps prevent missed steps and builds reliable habits.
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 Illinois Secretary of State — Driver Services administers this knowledge test as part of its commercial driver license program. To earn the CDL General Knowledge on your Illinois CDL, you need to score at least 40 out of 50 on the official version.
Topics covered on this practice test
- Inspection: 4 questions
- Backing: 3 questions
- Speed Management: 3 questions
- Driver Wellness: 3 questions
- CDL Rules: 2 questions
- Emergency Maneuvers: 2 questions
- Adverse Conditions: 2 questions
- Communication: 2 questions
- Night Driving: 1 question
- Cargo: 1 question
- Basic Control: 1 question
- Vehicle Dynamics: 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 Illinois 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 Illinois