CDL General Knowledge Practice Test
General Knowledge is the section every Class A and Class B applicant has to pass, and it is the longest one on the written exam. These practice questions come with the reasoning behind each answer, because knowing why a wrong answer is wrong is what gets you through the real test.
Written and reviewed by Christopher Scott Sneed, 30+ year diesel technician, founder of Blue Collar Empire.
What this section covers
- Vehicle inspection: what you check and in what order
- Basic control: shifting, backing, turning, and space management
- Safe driving: speed, following distance, and total stopping distance
- Seeing hazards, communicating, and controlling speed for conditions
- Night driving, mountain driving, extreme weather, and skid recovery
- Accident procedures, fires, and driver fitness rules including the 0.04 BAC limit
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How often must a driver complete a pre-trip inspection?
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15 practice questions with explanations
1. How often must a driver complete a pre-trip inspection?
- A. Once per week
- B. Before every trip — correct
- C. Only when the vehicle is new
- D. Only after a DOT inspection
Why: FMCSA requires a pre-trip inspection before operating any commercial motor vehicle.
2. What is the most common cause of serious skids?
- A. Underinflated tires
- B. Driving too fast for conditions — correct
- C. Worn brake shoes
- D. Cold weather
Why: Excessive speed for conditions is the #1 cause of loss-of-traction skids.
3. When driving at night, you should:
- A. Use high beams whenever possible
- B. Adjust speed so you can stop within the range of your headlights — correct
- C. Follow closer to see the vehicle ahead
- D. Drive with interior lights on
Why: You must be able to stop within the distance you can see — headlight range at night.
4. Which is a sign of tire failure?
- A. Loud bang, vibration, or heavy steering pull — correct
- B. Slight fuel-economy drop
- C. A warm hub
- D. Steering that feels lighter than usual
Why: A blowout usually presents as a loud noise, vibration, or a hard pull to one side.
5. The proper way to hold the steering wheel is:
- A. One hand at 12 o'clock
- B. Both hands on opposite sides of the wheel — correct
- C. Bottom of the wheel only
- D. Whichever is comfortable
Why: Hands on opposite sides gives maximum control if a tire blows or the wheel jerks.
6. You should downshift before:
- A. Starting down a hill or entering a curve — correct
- B. Every stop
- C. Passing another vehicle
- D. Backing up
Why: Downshift before hills and curves so you keep engine braking and control.
7. Hydroplaning is most likely when:
- A. Tires are new
- B. Speed is high and roads are wet — correct
- C. The load is heavy
- D. Brakes are cold
Why: At higher speeds on wet roads, tires can lift off the surface on a film of water.
8. The best way to see the sides and rear of your rig is:
- A. Rely on your memory
- B. Regular mirror checks every 5–8 seconds — correct
- C. Only when changing lanes
- D. Only in traffic
Why: Frequent mirror scans catch problems (traffic, tires, cargo, smoke) early.
9. If your vehicle catches fire while driving, you should first:
- A. Speed up to blow the fire out
- B. Get off the road and stop in a safe place — correct
- C. Continue to the next exit no matter how far
- D. Open the hood immediately
Why: Pull over safely away from other traffic and combustibles before dealing with the fire.
10. Total stopping distance equals:
- A. Perception + reaction + braking distance — correct
- B. Braking distance only
- C. Reaction distance only
- D. Following distance
Why: Total stopping distance = perception distance + reaction distance + braking distance.
11. Following distance for a 60-ft rig at 55 mph in good conditions is at least:
- A. 2 seconds
- B. 4 seconds
- C. 7 seconds — correct
- D. 10 seconds
Why: One second per 10 ft of vehicle length up to 40 mph, +1 second above 40 mph = 7s for a 60-ft rig at 55 mph.
12. A driver may not operate a CMV with a blood alcohol concentration (BAC) of:
- A. 0.08 or higher
- B. 0.04 or higher — correct
- C. 0.10 or higher
- D. 0.02 or higher
Why: The federal CDL limit is 0.04% BAC — half the passenger-car limit.
13. Black ice is most likely on:
- A. Dry hilltops
- B. Bridges and shaded areas after rain or thaw — correct
- C. New asphalt
- D. Gravel roads
Why: Bridges and shaded spots freeze first because they lose heat from both sides.
14. If your brakes fail on a downgrade, you should:
- A. Shift to neutral and coast
- B. Look for an escape ramp and use engine braking — correct
- C. Pump the brakes only
- D. Turn off the engine
Why: Use engine braking and steer to an escape ramp; never shift to neutral.
15. You should never drive with cruise control in:
- A. Heavy rain, snow, or ice — correct
- B. Flat highway
- C. Interstate at night
- D. Any downhill
Why: Cruise can maintain speed into a loss of traction, causing a skid.
How to study this section
- Learn total stopping distance as a formula, not a number — perception plus reaction plus braking.
- Memorize the following-distance rule: one second per 10 feet of vehicle length up to 40 mph, plus one second above 40 mph.
- Every question about speed and conditions has the same underlying answer: slow down.
- Read your state's official CDL manual alongside these questions — the exam is written from it.
Frequently asked questions
- How many questions are on the CDL general knowledge test?
- Most states use about 50 multiple-choice questions and require roughly 80% correct to pass. Check your state's CDL manual, because question counts and passing scores vary.
- Is the general knowledge test required for every CDL?
- Yes. Every Class A, B, and C applicant takes General Knowledge. Endorsements and Air Brakes are additional tests on top of it.
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