General Knowledge (national) practice test
50 questions · 80% to pass · Required for every CDL applicant.
How to use this practice test
Read each question, click an answer, and the correct choice is highlighted with a short explanation referencing the underlying CDL Manual concept. Your live score appears at the top of the page. Refresh to reset.
This test runs entirely in your browser. Nothing is uploaded; no account is required. Pages refresh to a new randomized cut from the bank.
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1. When backing a commercial vehicle, you should:
Explanation. Backing toward the driver side gives the driver a direct line of sight, which is much safer than blind-side backing.
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2. Texting while driving a CMV is:
Explanation. Texting is banned for all CMV drivers under federal law.
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3. When checking your vehicle, the engine should be off and the wheels chocked because:
Explanation. Chocking wheels and shutting down the engine prevents the vehicle from rolling away while you are underneath or alongside it.
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4. You should signal a lane change for at least:
Explanation. Signal early and continuously enough for surrounding traffic to see your intent.
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5. Per federal regulations, controlled braking means:
Explanation. Controlled braking is firm pressure that does not lock the wheels, allowing you to continue steering. (Reinforcement variant — same underlying CDL Manual concept.)
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6. When driving in fog, you should:
Explanation. High beams reflect off fog and reduce vision; low beams and slower speed are correct.
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7. In real-world commercial driving, hydroplaning is most likely when:
Explanation. Hydroplaning can occur at speeds as low as 30 mph if there is enough water and the tires cannot channel it away. (Reinforcement variant — same underlying CDL Manual concept.)
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8. The 14-hour rule means a driver may not drive after the:
Explanation. After 14 consecutive hours on duty following 10 hours off, no further driving is allowed even if some of those 14 hours were not driving.
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9. When operating a CMV in interstate commerce, a vehicle is most likely to roll over when:
Explanation. High center of gravity plus sudden steering or braking is the recipe for rollovers. (Reinforcement variant — same underlying CDL Manual concept.)
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10. During a pre-trip inspection, communicating presence with the horn is appropriate when:
Explanation. Use the horn only to warn others of your presence when there is a real risk they have not seen you. (Reinforcement variant — same underlying CDL Manual concept.)
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11. When checking lights during the pre-trip, you should turn the key on and:
Explanation. Have someone else watch, or turn lights on and off and walk around to verify each lamp is working.
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12. What is the standard color of a placard for a Class 2 (gases) hazardous material?
Explanation. Class 2 placards are red for flammable gas, green for non-flammable, and yellow/white for poison/oxygen subdivisions.
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13. Most state DMV CDL handbooks state that you should signal continuously when turning because:
Explanation. Continuous signaling keeps other drivers informed and prevents the signal from cancelling before the turn is complete. (Reinforcement variant — same underlying CDL Manual concept.)
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14. Most state DMV CDL handbooks state that brake fade is caused by:
Explanation. Brakes lose effectiveness when overheated; this is why low gears are essential on grades. (Reinforcement variant — same underlying CDL Manual concept.)
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15. Most state DMV CDL handbooks state that when making a right turn in a large vehicle, you should:
Explanation. Stay in the right lane and watch the trailer; swinging left first invites a same-direction driver to squeeze in on your right. (Reinforcement variant — same underlying CDL Manual concept.)
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16. During a pre-trip inspection, which is the best way to handle a tire failure?
Explanation. Hard braking after a tire failure can cause loss of control. Hold the wheel firmly, ease off the throttle, and brake gently after slowing. (Reinforcement variant — same underlying CDL Manual concept.)
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17. When operating a CMV in interstate commerce, when checking your vehicle, the engine should be off and the wheels chocked because:
Explanation. Chocking wheels and shutting down the engine prevents the vehicle from rolling away while you are underneath or alongside it. (Reinforcement variant — same underlying CDL Manual concept.)
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18. In real-world commercial driving, a safe following distance for a 40-foot vehicle at 50 mph is at least:
Explanation. Use 1 second per 10 feet of vehicle length under 40 mph, plus 1 extra second above 40 mph: 4 + 1 = 5 seconds for a 40-foot truck at 50 mph. (Reinforcement variant — same underlying CDL Manual concept.)
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19. Per federal regulations, which of these is NOT a sign of a tired driver?
Explanation. A "second wind" is a brief, deceptive boost. All of the others, including the second wind, are warning signs of fatigue. (Reinforcement variant — same underlying CDL Manual concept.)
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20. According to the FMCSA CDL Manual, most pre-trip inspections begin with which step?
Explanation. The CDL Manual lists "review last inspection report" as the first step in the seven-step pre-trip inspection. (Reinforcement variant — same underlying CDL Manual concept.)
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21. Which is the best way to handle a tire failure?
Explanation. Hard braking after a tire failure can cause loss of control. Hold the wheel firmly, ease off the throttle, and brake gently after slowing.
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22. When operating a CMV in interstate commerce, empty trucks need:
Explanation. Empty trucks have less traction and brakes designed for the loaded weight, so they can actually take longer to stop and lock up more easily. (Reinforcement variant — same underlying CDL Manual concept.)
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23. Controlled braking means:
Explanation. Controlled braking is firm pressure that does not lock the wheels, allowing you to continue steering.
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24. When taking the CDL knowledge exam, when checking your vehicle, the engine should be off and the wheels chocked because:
Explanation. Chocking wheels and shutting down the engine prevents the vehicle from rolling away while you are underneath or alongside it. (Reinforcement variant — same underlying CDL Manual concept.)
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25. Empty trucks need:
Explanation. Empty trucks have less traction and brakes designed for the loaded weight, so they can actually take longer to stop and lock up more easily.
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26. Per federal regulations, you should signal continuously when turning because:
Explanation. Continuous signaling keeps other drivers informed and prevents the signal from cancelling before the turn is complete. (Reinforcement variant — same underlying CDL Manual concept.)
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27. The eye-lead time recommended for highway driving is at least:
Explanation. Look 12-15 seconds ahead so you can identify hazards in time to react smoothly.
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28. A driver loses their CDL for life if convicted of:
Explanation. Using a CMV to commit a controlled-substance felony is grounds for a lifetime CDL disqualification.
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29. When taking the CDL knowledge exam, you should NOT drive when taking which of these?
Explanation. Drowsiness-causing medications, even legal ones, can disqualify you from driving. (Reinforcement variant — same underlying CDL Manual concept.)
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30. Per federal regulations, you should warm up the engine before driving because:
Explanation. Allowing the engine to warm circulates oil and reduces wear before load is applied. (Reinforcement variant — same underlying CDL Manual concept.)
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31. When making a right turn in a large vehicle, you should:
Explanation. Stay in the right lane and watch the trailer; swinging left first invites a same-direction driver to squeeze in on your right.
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32. According to the FMCSA CDL Manual, a retarder helps the driver by:
Explanation. Retarders slow the vehicle without using service brakes, reducing brake wear and overheating risk. (Reinforcement variant — same underlying CDL Manual concept.)
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33. Experienced commercial drivers know that you must use low beams within how many feet of an oncoming vehicle?
Explanation. Switch to low beams within 500 feet of an oncoming vehicle to avoid blinding the other driver. (Reinforcement variant — same underlying CDL Manual concept.)
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34. Per federal regulations, when driving in fog, you should:
Explanation. High beams reflect off fog and reduce vision; low beams and slower speed are correct. (Reinforcement variant — same underlying CDL Manual concept.)
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35. Black ice is dangerous because:
Explanation. Black ice is a thin layer of ice clear enough that the road below shows through, making it look merely wet.
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36. When taking the CDL knowledge exam, black ice is dangerous because:
Explanation. Black ice is a thin layer of ice clear enough that the road below shows through, making it look merely wet. (Reinforcement variant — same underlying CDL Manual concept.)
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37. When operating a CMV in interstate commerce, what does the term "perception distance" mean?
Explanation. Perception distance is the distance traveled while your brain identifies a hazard, typically about 1.5 seconds at highway speed. (Reinforcement variant — same underlying CDL Manual concept.)
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38. When taking the CDL knowledge exam, what does the term "perception distance" mean?
Explanation. Perception distance is the distance traveled while your brain identifies a hazard, typically about 1.5 seconds at highway speed. (Reinforcement variant — same underlying CDL Manual concept.)
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39. During a pre-trip inspection, you should check your mirrors:
Explanation. Frequent mirror checks (every 5-8 seconds) are part of safe scanning. (Reinforcement variant — same underlying CDL Manual concept.)
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40. In real-world commercial driving, brake fade is caused by:
Explanation. Brakes lose effectiveness when overheated; this is why low gears are essential on grades. (Reinforcement variant — same underlying CDL Manual concept.)
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41. According to the FMCSA CDL Manual, cargo should be inspected:
Explanation. You must inspect cargo within the first 50 miles, then every 150 miles or 3 hours, whichever is sooner. (Reinforcement variant — same underlying CDL Manual concept.)
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42. In real-world commercial driving, when approaching a railroad crossing, you should:
Explanation. Always slow, look, listen, and prepare to stop. A full stop is required only for buses, hazmat, and certain placarded vehicles. (Reinforcement variant — same underlying CDL Manual concept.)
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43. In real-world commercial driving, when driving in fog, you should:
Explanation. High beams reflect off fog and reduce vision; low beams and slower speed are correct. (Reinforcement variant — same underlying CDL Manual concept.)
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44. When taking the CDL knowledge exam, when checking lights during the pre-trip, you should turn the key on and:
Explanation. Have someone else watch, or turn lights on and off and walk around to verify each lamp is working. (Reinforcement variant — same underlying CDL Manual concept.)
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45. A driver may use a hand-held mobile phone while driving a CMV:
Explanation. Federal rules prohibit hand-held mobile phone use by CMV drivers except in emergencies.
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46. Most state DMV CDL handbooks state that when driving in fog, you should:
Explanation. High beams reflect off fog and reduce vision; low beams and slower speed are correct. (Reinforcement variant — same underlying CDL Manual concept.)
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47. Most state DMV CDL handbooks state that you should signal a lane change for at least:
Explanation. Signal early and continuously enough for surrounding traffic to see your intent. (Reinforcement variant — same underlying CDL Manual concept.)
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48. You should warm up the engine before driving because:
Explanation. Allowing the engine to warm circulates oil and reduces wear before load is applied.
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49. Which of these is NOT a sign of a tired driver?
Explanation. A "second wind" is a brief, deceptive boost. All of the others, including the second wind, are warning signs of fatigue.
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50. Per federal regulations, when driving down a long, steep grade, you should:
Explanation. Always select a low gear before descending so engine compression helps hold speed and brakes do not overheat. (Reinforcement variant — same underlying CDL Manual concept.)
About the General Knowledge exam
The General Knowledge exam is required for every Class A, B, and C CDL applicant. It covers vehicle inspection, basic control, shifting, backing, communicating with other drivers, distracted driving, fatigue, hazard perception, emergency maneuvers, skid control, accident procedures, hazardous materials awareness, and federal hours-of-service rules.
This is the national edition of the General Knowledge practice test. Visit your state page for a state-framed version of the same exam. The questions are identical because the federal source material is identical — only the wording around the test changes from state to state.
Tips that actually work
- Read every answer choice before clicking. CDL questions are famous for "best answer" wording where two choices look right.
- Don’t memorize question text — learn the underlying rule. The DMV reshuffles wording constantly.
- Keep a list of the questions you miss. Re-drill them in isolation until you can’t miss them.
- Practice in short, frequent sessions. Two 20-minute sessions per day beats one two-hour cram.
What happens after I pass?
Passing the knowledge test earns you a Commercial Learner’s Permit (CLP). You must hold the CLP for at least 14 days before you can take the road skills test, and you must drive with a CDL-holding instructor in the cab during that period. Once you pass the road skills test, your CDL is issued.