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CDL General KnowledgeFree Commercial Driver's License — General Knowledge practice test
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10 real CDL General Knowledge practice questions with instant answers and explanations — no account, no credit card, no email. Score yourself, then unlock the full bank of 70 questions whenever you’re ready. The CDL General Knowledge passing score is 80% (typically 40 of 50).
What is the main reason a commercial driver performs a pre-trip inspection before every trip?
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All 10 CDL General Knowledge questions & answers
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Q1. What is the main reason a commercial driver performs a pre-trip inspection before every trip?
Correct answer: B. To find problems that could cause a crash or breakdown before driving
The purpose of the pre-trip inspection is safety: catching mechanical problems before they cause a crash or a breakdown on the road.
Q2. Who is ultimately responsible for making sure a commercial vehicle is in safe operating condition before it is driven?
Correct answer: C. The driver
The driver is responsible for inspecting the vehicle and confirming it is safe to operate; the driver must not drive a vehicle found to be unsafe.
Q3. During a routine trip, when should a driver perform en-route inspection checks such as glancing at gauges and watching for tire or brake problems?
Correct answer: B. Periodically while driving and at each stop along the way
En-route inspections are done throughout the trip: watching gauges, mirrors, and the feel of the vehicle while driving and checking critical items at stops.
Q4. In the recommended seven-step inspection method, which step is performed first?
Correct answer: B. A vehicle overview and reviewing the last inspection report
The seven-step method begins with an overview of the vehicle and a review of any prior inspection report noting defects that should have been repaired.
Q5. For steering-axle (front) tires, what is the minimum legal tread depth for a commercial vehicle?
Correct answer: C. 4/32 inch
Federal standards require at least 4/32 inch of tread on steering-axle tires; other tires must have at least 2/32 inch.
Q6. During the in-cab portion of the inspection, checking that the parking brake and service brakes hold is important because it confirms:
Correct answer: B. The braking system can safely stop and hold the vehicle
Checking that the parking and service brakes hold and stop the vehicle verifies the braking system is working before you rely on it in traffic.
Q7. When inspecting the fifth wheel and coupling on a tractor-trailer, what is a key thing to verify?
Correct answer: B. That the locking jaws are closed around the kingpin and the release arm is secured
A proper coupling requires the fifth-wheel locking jaws to be fully closed around the kingpin with the release handle in the locked position; a gap or open jaws means the trailer is not secure.
Q8. Which items are part of the emergency equipment a commercial vehicle must carry?
Correct answer: B. A properly charged and rated fire extinguisher, spare electrical fuses (if used), and warning devices such as reflective triangles
Required emergency equipment includes a properly charged fire extinguisher, spare fuses for vehicles that use them, and warning devices such as three reflective triangles.
Q9. While checking the engine compartment during a pre-trip inspection, the engine should be:
Correct answer: B. Off, with the key removed and wheels chocked as needed
The engine-compartment inspection is done with the engine off to safely check belts, hoses, and fluid levels without risk from moving parts.
Q10. A driver notices a steady puddle of oily fluid forming under the tractor during the walk-around. What is the correct response?
Correct answer: B. Identify the source of the leak and have it corrected before driving
Fresh leaks indicate a developing problem; the driver should identify the source and have it repaired rather than drive with an active fluid leak.
Exam facts and objectives sourced from the official FMCSA (Commercial Driver License Program) certification page. Last reviewed June 2026.
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