South Carolina SCDMV CDL General Knowledge Practice Test 4
Test 4 of 5. Pick an answer for each question to see if it is right and why; your score appears at the end. You need 40 correct answers to pass, the same ratio as the real South Carolina test.
- Questions50
- Correct to pass40
- Passing score80%
- Minimum age18 years
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1. Why must the downshift be finished before you reach a steep downgrade or a sharp curve rather than during it?
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Answer D: Because once your speed is too high you may not get into any gear at all
If you wait until speed has built up, the lower gear may refuse to engage and you can be left in neutral with no engine braking at all.
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2. A hard frost has left your vehicle covered in ice. What must be cleared before you drive?
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Answer D: The windshield, mirrors, lights and reflectors
You must be able to see out and other drivers must be able to see your lights and reflectors, so all of those surfaces have to be cleared.
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3. On the Interstate System, what are the federal maximums for a tandem axle group and for gross vehicle weight?
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Answer B: 34,000 pounds and 80,000 pounds
The federal Interstate limits allow 34,000 pounds on a tandem axle group and 80,000 pounds gross.
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4. What is wrong with resting your foot on the clutch pedal between shifts?
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Answer B: It slowly wears the clutch out, because the pressure plate is never fully engaged
Any weight on the pedal partly disengages the clutch, so it slips and wears; the foot belongs off the pedal once the shift is finished.
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5. How much sleep does a typical adult driver need each day to stay properly alert?
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Answer D: Seven to eight hours
Most adults need seven to eight hours of sleep in every 24 hours, and a driver who regularly gets less builds up a debt that shows up behind the wheel.
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6. Why is backing toward the driver side preferred?
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Answer C: You can watch the rear of the vehicle directly through the side window
Backing to the left lets the driver look out the window and see the rear of the vehicle directly instead of relying on a mirror alone.
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7. A load overhangs the rear of the trailer. What must the driver check before leaving?
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Answer D: That the overhang is marked as required, with flags or lamps as conditions demand
A projecting load has to be made visible to other drivers, with flags in daylight and lamps when lights are required, so nobody runs into what they cannot see.
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8. Under federal safety rules, what must the driver of a commercial vehicle do before starting a trip?
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Answer A: Be satisfied that the vehicle is in safe operating condition
The driver is responsible for inspecting the vehicle and must be satisfied it is in safe operating condition before the trip begins.
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9. While checking the in-cab gauges after start-up, what should the coolant temperature gauge do?
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Answer C: Rise gradually to the normal operating range
A healthy cooling system warms the engine slowly; a gauge that shoots up or stays cold points to a problem with the thermostat, coolant or sensor.
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10. Where is the yellow antilock brake malfunction lamp on a trailer, and what does it mean if it stays lit?
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Answer D: On the left side, at the front or rear corner, and it means the antilock function may not be working
Trailers carry the yellow lamp on the left side, and a lamp that stays on after the bulb check means the antilock function may be lost even though the normal brakes still work.
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11. Under federal rules, what is required of a commercial driver who wants to use a mobile phone while driving?
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Answer B: The phone must be hands-free and started with no more than a single button press, and it must not be held
Federal rules ban texting and hand-held phone use while driving a commercial vehicle; reaching for, holding or dialing a phone is a violation.
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12. You are hauling livestock and the trailer is only partly full. What should be done?
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Answer A: Use false bulkheads or partitions to keep the animals bunched together
Animals that can move around shift the center of gravity, so a partial load is bunched together with partitions to limit how far the weight can move.
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13. A tire has a cut deep enough to expose the body ply or the belt material. What does that mean?
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Answer D: The vehicle must not be driven on that tire
Once the structural plies are exposed the casing has lost its strength, and federal rules treat that tire as unfit for the road.
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14. Why should the mirrors be checked repeatedly while you make a tight turn?
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Answer C: To watch the rear of the vehicle clear other vehicles and objects
In a long vehicle the rear wheels cut inside the path of the front wheels, so only the mirrors show whether the rear is clearing curbs, poles and other vehicles.
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15. With water standing on the road, hydroplaning can begin at speeds as low as what?
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Answer D: 30 mph
When enough water covers the surface, the tires can ride up on it and lose contact at speeds as low as 30 mph.
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16. Which of these is NOT on the federal list of parts and accessories the driver must be satisfied are in good working order before driving?
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Answer D: The seat cushion upholstery
The federal pre-trip rule names brakes, steering, lights and reflectors, tires, horn, wipers, mirrors, coupling devices, wheels and rims, and emergency equipment; seat upholstery is not on that list.
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17. You are pulling a loaded pneumatic dry bulk trailer and approach an exit ramp posted at 35 mph. What is the safest approach?
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Answer C: Slow to well below the posted speed before the ramp begins
A dry bulk trailer carries its weight high and the load can move, so the ramp speed posted for a car is far too fast and the slowing must be finished before the curve.
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18. When should a driver add space beyond the basic following distance rule?
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Answer D: On slippery roads and whenever visibility is poor
The seconds rule is a minimum for good conditions, so rain, snow, darkness and heavy traffic all call for more space than that.
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19. After starting the engine, how quickly should the oil pressure gauge come up to its normal range?
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Answer B: Within a few seconds
Oil pressure should build within seconds of starting; if it stays low, the engine is not being lubricated and should be shut down.
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20. You are drifting in the lane, yawning constantly and cannot remember the last few miles. What is the only reliable cure?
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Answer C: Stopping in a safe place and sleeping
Those are classic drowsiness warning signs, and nothing except sleep repays the sleep the body is missing.
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21. Who may South Carolina issue a seasonal restricted commercial driver's license to?
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Answer B: A seasonal employee of a custom harvester, livestock feeder, or agri-chemical business who holds a Class E or F license
Section 56-1-2085(C) limits the seasonal restricted CDL to seasonal agricultural employees who hold or pass a Class E or F license and have at least a year of driving experience.
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22. Why does a driver use pull-ups while backing into a tight space?
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Answer C: To pull forward and start the approach again when the angle is going wrong
Stopping, pulling ahead and repositioning fixes a bad angle safely, and there is nothing wrong with needing more than one attempt.
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23. What does a front-end header board on a van or flatbed protect against?
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Answer A: Cargo moving forward toward the cab in a crash or hard stop
The header board, often called a headache rack, blocks forward movement of the load toward the driver.
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24. What must happen to a commercial driver found with a measurable amount of alcohol in his system, or who refuses the alcohol test, under South Carolina law?
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Answer D: The driver must be placed out-of-service for 24 hours
Section 56-1-2120(B) requires a 24-hour out-of-service period for a commercial driver with measurable alcohol or who refuses testing.
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25. Using the snub braking method on a downgrade, when does the driver release the brakes?
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Answer A: After speed has dropped about 5 mph below the safe speed
The driver brakes firmly to about 5 mph under the chosen safe speed, releases to let the brakes cool, then repeats when the safe speed returns.
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26. Your axle weights are legal, but the tires on that axle are rated below the weight it is carrying. What controls?
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Answer B: The lower figure, so the tires may not be loaded beyond their marked rating
You may never exceed the rating marked on a tire, even when the axle limit would allow more, because an overloaded tire builds heat and can fail.
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27. What actually lowers the amount of alcohol in the bloodstream?
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Answer B: Time
The liver removes alcohol at a fixed rate, so nothing but the passage of time reduces blood alcohol concentration.
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28. Where on a tire is tread depth measured?
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Answer C: In a major tread groove, away from any tie bar or wear indicator
Depth is taken in a major groove and away from the raised tie bars and wear indicators, which would give a shallower and misleading reading.
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29. A brake light lens is cracked and the lamp still lights. How should that be treated?
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Answer B: As a defect, because water can enter and the lamp can dim or fail
A cracked lens lets in water and dirt, which corrodes the socket and dulls the lamp, so it is reported before it becomes a dead brake light.
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30. As a long vehicle goes around a corner, how do the rear wheels travel compared with the front wheels?
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Answer A: They follow a tighter path, closer to the inside of the turn
The rear wheels off-track toward the inside of the turn, and the longer the vehicle the bigger the difference, which is why the front must swing wide enough to keep the rear off the curb.
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31. Your speedometer stops working during the pre-trip check. How should it be treated?
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Answer D: As a defect, because the driver cannot judge and control speed without it
A working speedometer is required equipment, because judging speed by feel in a heavy vehicle is unreliable and speed governs stopping distance.
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32. Which of these counts as a serious traffic violation for a commercial driver license holder?
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Answer C: Speeding 15 miles per hour or more above the limit
Excessive speeding, reckless driving, improper lane changes, following too closely and texting while driving are all serious traffic violations.
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33. Which combination of warning devices meets the requirement for a stopped commercial vehicle?
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Answer A: Three reflective triangles, or six fusees, or three liquid burning flares
A vehicle may carry three bidirectional reflective triangles, six fusees or three liquid burning flares as its warning devices.
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34. A tire blows out at highway speed. What should the driver do first?
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Answer C: Hold the steering wheel firmly, stay off the brake and let the vehicle slow down
Braking while a tire is gone can pull the vehicle out of line, so the driver keeps it straight and lets speed fall before easing off the road.
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35. What ages does South Carolina apply to commercial driving inside and outside the state?
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Answer C: At least 18 to drive within South Carolina and at least 21 to drive outside it
SCDMV states that a first CDL requires the driver to be at least 18 to drive within South Carolina and at least 21 to drive outside the state.
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36. You have just passed another vehicle on a two lane road. What tells you it is safe to return to your lane?
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Answer B: You can see the whole front of that vehicle in your right mirror
Seeing the entire front of the vehicle you passed in your mirror proves you are far enough ahead to move back over without cutting the driver off.
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37. How is a shipping container normally secured when it is carried on a special container chassis?
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Answer B: With its own locking devices that attach the container directly to the chassis frame
Containers built for rail or ship transport have locking corners that fasten to a matching chassis; a container carried on a plain flatbed must be secured like any other cargo.
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38. What is the purpose of the header board, or headache rack, that you inspect behind the cab?
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Answer A: It protects the driver from cargo that shifts forward during a hard stop
In a hard stop the load keeps moving forward, and the header board is the barrier between that load and the back of the cab.
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39. What condition should the fifth wheel be in before you back under a trailer?
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Answer C: Jaws open, plate greased, and the fifth wheel tilted down toward the rear
The jaws have to be open to take the kingpin, the plate must be lubricated to prevent hard steering, and the fifth wheel is tilted down at the rear so the trailer apron can ride up onto it.
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40. How should a driver use brakes fitted with an antilock system during an emergency stop?
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Answer C: Brake as usual and keep enough pressure to stay in control while steering around the hazard
The system only works when the brakes are applied hard enough for it to act, so the driver keeps pressure on and steers while the system prevents lockup.
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41. You must drive well below the speed of surrounding traffic, for example when climbing a steep grade with a heavy load. What should you do?
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Answer B: Turn on the four-way flashers to warn following traffic, where state law allows it
Flashers warn faster traffic that a slow-moving vehicle is ahead, which helps prevent rear-end crashes; some states restrict their use while moving, so check the local rule.
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42. What does mountain driving demand that flat country driving does not?
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Answer D: Lower gears and constant allowance for gravity
In the mountains gravity works for you on the climb and against you on the descent, so gear selection and speed control matter far more than on level road.
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43. Your load projects more than 4 feet beyond the rear of the vehicle. How must the projecting end be marked?
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Answer A: With a red or orange flag by day and a red lamp after dark
Federal rules require a warning flag on a rear projecting load in daylight and a red lamp on the end of it when lights are required.
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44. You are backing with a helper guiding you and the helper drops out of sight in your mirror. What should you do?
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Answer B: Stop until you can see the helper again
If you cannot see the helper you cannot receive a signal to stop, so the only safe action is to halt until visual contact is restored.
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45. Your brakes have failed on a downgrade and there is no escape ramp in sight. What is the best choice?
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Answer A: Steer into an open field or onto a side road that flattens out or climbs uphill
A flat or uphill escape route uses gravity and rolling resistance to stop the vehicle; take it as soon as you see it, because the longer you wait the faster you go.
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46. Why can an empty truck need a longer stopping distance than a loaded one?
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Answer C: An empty vehicle has less traction, so its wheels lock up more easily
Brakes and tires are designed for a loaded vehicle, and with little weight on the axles the tires grip less and lock sooner.
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47. How long must the record of a periodic inspection be kept?
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Answer A: Fourteen months
The periodic inspection report is retained for fourteen months from the date of the report, which covers the full twelve month cycle plus a margin.
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48. What can repeated violations of the federal phone and texting rules cost a commercial driver?
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Answer D: Disqualification of the commercial driver license
Multiple convictions for using a hand-held phone or texting while driving a commercial vehicle lead to disqualification, on top of fines for driver and carrier.
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49. Why should you never shift gears while crossing railroad tracks?
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Answer A: You could miss the gear or stall and be stuck on the tracks
A stalled or coasting vehicle on the tracks has no way to clear quickly, so choose the gear before the crossing and do not shift until you are across.
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50. A hazard suddenly appears ahead and you must act. Which is usually the faster way to avoid it in a heavy vehicle?
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Answer B: Steering around it, because you can usually turn faster than you can stop
Stopping distance at speed is very long, so a quick turn out of the way, when there is room, avoids the crash sooner than braking.