South Carolina SCDMV CDL General Knowledge Practice Test 5
Test 5 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. What is checked about the clutch and the gearshift during the in-cab inspection?
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Answer D: That the clutch free play is within the range the manufacturer specifies
Too little or too much clutch free play causes slipping or dragging, either of which can leave the driver unable to select the gear a hill demands.
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2. An unblocked crate 4 feet long and weighing 900 pounds needs at least how many tiedowns?
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Answer D: One
An article 5 feet or less in length and 1,100 pounds or less in weight is covered by a minimum of one tiedown.
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3. You are moving an oversized load under a permit that requires a pilot vehicle. What is the pilot vehicle there to do?
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Answer B: Warn other traffic and check the route ahead for clearances and hazards
Escort or pilot vehicles warn approaching traffic and scout the route for low bridges, narrow spots and other hazards that a wide or long load cannot pass.
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4. What are you checking when you pull the engine oil dipstick during the pre-trip?
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Answer A: That the oil level is within the safe operating range marked on the stick
The dipstick shows whether there is enough oil to lubricate and cool the engine, and a level outside the safe range must be corrected before driving.
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5. You are dropping a loaded trailer in a yard. How far should the landing gear be lowered?
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Answer A: Until the pads make firm contact and the trailer weight is just off the fifth wheel
Cranking down until the gear is firmly on the ground and just lifting the load off the fifth wheel makes the trailer stable and lets the tractor pull out cleanly.
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6. The scale shows that your combination is over the legal gross weight. Why will sliding the tandems not fix it?
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Answer B: Because sliding the axles changes where the weight sits, not how much there is
Repositioning axles redistributes weight between axle groups; when the total is too high, freight has to come off the vehicle.
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7. Which wheel or rim condition must be treated as a defect during the walkaround?
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Answer C: Cracks, illegal welded repairs, or missing and loose lug nuts
Cracked or welded rims and missing or loose fasteners can let a wheel separate from the vehicle and must be corrected before driving.
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8. What does South Carolina charge for commercial driver license skills tests?
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Answer B: The first skills test is free and each later one costs 25 dollars
State law makes the first CDL skills test administered by the department free of charge and allows a 25 dollar fee for each subsequent skills test given to that individual.
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9. Why does a load of live animals need special attention?
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Answer D: The animals move and lean, so the center of gravity shifts and the vehicle can be pushed off balance in a turn
A live load will not stay where it is put, and that movement changes the balance of the vehicle exactly when a curve is loading it most.
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10. What is normally required in order to move an over-width or over-length load?
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Answer B: A special permit along with warning devices such as flags and signs
Oversize movements need a permit plus marking devices, and travel is often limited to certain hours or routes.
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11. An overpass you have driven under before now has a fresh layer of pavement on the road below it. Why does that matter?
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Answer B: The new layer raises the road and reduces the clearance
Repaving lifts the road surface, so the real clearance under a structure can be less than the height posted on it.
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12. What must be checked about the cargo doors and any tarpaulin before a trip?
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Answer B: That the doors are closed and latched and that any tarp is tied down securely
An unlatched door or a loose tarp can swing open or tear free at speed, spilling cargo or blocking the view of the traffic behind you.
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13. Where are regrooved, recapped or retreaded tires not allowed on a truck or truck tractor?
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Answer C: On the front steering wheels
Regrooved and retreaded tires are prohibited on the front wheels of a truck or truck tractor because a steering tire blowout is extremely difficult to manage.
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14. What is the basic rule about backing a large vehicle?
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Answer B: Avoid backing whenever there is another way
Backing is dangerous because you cannot see everything behind you, so the manual tells drivers to plan routes and parking that avoid it.
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15. How long is a commercial driver disqualified from operating a commercial motor vehicle after a first conviction for an offense such as driving under the influence, refusing a chemical test, or leaving the scene of an accident?
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Answer D: Not less than one year
Section 56-1-2110(A) sets a minimum one-year disqualification for a first conviction of these offenses.
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16. Experienced commercial drivers scan the road ahead by roughly how much travel time?
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Answer B: About 12 to 15 seconds
Looking 12 to 15 seconds ahead gives a heavy vehicle enough room to slow or change lanes smoothly instead of reacting late.
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17. Before raising the hood to inspect the engine compartment, what should you do?
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Answer B: Shut off the engine, set the parking brake and chock the wheels if needed
The engine compartment is inspected with the engine off and the vehicle secured so nothing can move or turn while your hands are inside.
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18. How does South Carolina change the one-year commercial disqualification period when the offense occurred while the driver was transporting a placarded load of hazardous material?
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Answer A: The minimum disqualification rises to not less than three years
Section 56-1-2110(A) raises the minimum disqualification to three years when the violation occurs while hauling a placarded hazardous material load.
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19. What is the risk when too little weight rests on the drive axles?
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Answer A: Poor traction, so the drive wheels spin easily on wet or slippery surfaces
Traction depends on weight pressing the driving tires onto the road, so a light drive axle spins on wet, snowy or loose surfaces.
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20. Which of these is a major cause of skids in heavy vehicles?
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Answer C: Over-braking, over-steering, over-acceleration or driving too fast for conditions
Skids happen when the tires are asked for more grip than the road can give, which happens through braking, steering or accelerating too hard or simply too much speed.
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21. Federal rules forbid operating a commercial vehicle in which condition?
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Answer C: In a condition likely to cause a crash or a breakdown
A defect that makes a crash or a breakdown likely has to be corrected before the vehicle is driven, not reported at the end of the trip.
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22. What does the federal bridge formula do?
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Answer C: It reduces the weight allowed on a group of axles as those axles get closer together
Axles bunched together concentrate the load on a short span of a bridge, so the formula lowers the allowable weight as the spacing shrinks.
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23. You are hauling a load of steel plate that is well within every weight limit but is stacked five feet high on a flatbed. What is the main concern?
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Answer A: The center of gravity is high, so the rig will roll more easily in a curve
Legal weight does not make a load safe; height raises the center of gravity and it is height, not weight alone, that decides how readily the vehicle rolls over.
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24. A fire starts in the cargo area of a van trailer. Why should you keep the doors closed until firefighters arrive?
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Answer D: Opening the doors lets in air that feeds the fire
A fire in a closed van is starved of oxygen; opening the doors gives it the air it needs to flare up.
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25. Most rollovers of loaded trucks on exit and entrance ramps happen for which reason?
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Answer B: The ramp was taken faster than the load could tolerate
A posted ramp speed is set for cars, and a loaded trailer with a high center of gravity can roll at a speed a car would take easily.
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26. Which items belong to the trailer part of the walkaround inspection?
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Answer D: Landing gear, doors, tires, wheels, lights, reflectors, frame and cargo securement
The trailer has its own running gear, lighting, structure and load, and all of it is the responsibility of the driver pulling it.
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27. On a one way street or a divided highway, where are the warning devices placed?
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Answer B: About 10 feet, 100 feet and 200 feet back toward the approaching traffic
When traffic can only come from one side, all three devices are spread out behind the vehicle to give approaching drivers a longer warning.
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28. What should be done before a night trip to get the most from your headlights?
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Answer C: Clean the windshield, the mirrors and the lights
Dirt on glass and lenses cuts both the light you throw down the road and the light that reaches your eyes, so cleaning is the cheapest night safety measure there is.
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29. During the walkaround inspection, where does the driver normally start and how does the check proceed?
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Answer C: At the left front of the vehicle, working around it in a set order that returns to the cab
The walkaround follows the same route every time, starting at the left front and circling the vehicle, so that nothing is skipped when the driver is tired or rushed.
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30. Your brakes are starting to fade on a mountain downgrade and a sign shows an escape ramp one mile ahead. What should you do?
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Answer B: Plan to use the ramp instead of trying to reach the bottom
Fading brakes on a grade only get worse, and the ramp exists precisely so a driver does not have to gamble on the rest of the descent.
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31. A company mechanic serviced your truck this morning and signed the work order. Do you still have to inspect the vehicle?
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Answer B: Yes, the driver is still responsible for being satisfied the vehicle is safe
Shop work does not transfer the duty; the driver who takes the vehicle out remains responsible for being satisfied it is in safe operating condition.
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32. You are backing a tractor-trailer in a straight line and the trailer starts to drift to the left. What is the standard correction?
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Answer D: Turn the top of the steering wheel a little to the left, toward the drift
Small corrections made in the direction the trailer is drifting bring it back into line; large or opposite movements make the drift worse.
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33. What is the correct way to test the parking brake before a trip?
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Answer C: With the parking brake set, put the vehicle in a low gear and gently try to move forward
A parking brake that holds against a gentle pull in low gear is working; if the vehicle moves, the brake needs adjustment or repair.
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34. A doctor prescribes you a medicine that can cause drowsiness. What should you do?
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Answer A: Tell the doctor what you drive and not drive while affected
Both prescription and over the counter medicines can make a driver unsafe, so the medical professional must know the job and the driver must stay out of the seat while affected.
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35. Why does extra weight make a long downgrade more dangerous even when the brakes are in good order?
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Answer B: Gravity adds to the momentum and the brakes heat up faster
The heavier the vehicle, the more energy the brakes must turn into heat, and heat is exactly what makes brakes fade on a long descent.
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36. Which of these is a suspension defect you must look for during the walkaround?
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Answer D: Cracked or broken spring leaves, loose or broken U-bolts, or leaking air suspension bags
Broken springs, failed U-bolts and leaking air bags let the axle shift or the body drop, which can make the vehicle impossible to control.
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37. Part of your load stands high enough to hide a rear lamp or a reflector. What must be done?
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Answer B: The load must be moved or extra lamps fitted so the required lights can be seen
Required lamps and reflectors must remain visible; if the cargo blocks them, the load is rearranged or additional lamps are fitted so the vehicle can still be seen.
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38. How does a load carried high in the trailer affect safe speed through a curve?
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Answer B: It raises the rollover risk, so the speed must be lower
A high center of gravity lets the vehicle tip long before the tires lose their grip, so height of the load directly limits curve speed.
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39. For a modern truck with low-friction parts and a streamlined shape, which gear should be used going down a grade?
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Answer D: A gear lower than the one needed to climb the same grade
Newer trucks roll more freely than older ones, so the old rule of using the climbing gear no longer holds; a lower gear is needed for enough engine braking.
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40. How should speed and gears be handled when approaching a curve?
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Answer A: Slow to a safe speed and downshift before entering the curve
Braking and shifting are completed before the curve so the vehicle is settled and can pull gently through it without upsetting the load.
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41. Two vehicles of exactly the same length make a right turn, one gently and one very tightly. What is the effect on off-tracking?
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Answer A: Turning more sharply increases off-tracking, so the tight turn needs more room
Off-tracking depends on both the length of the vehicle and the sharpness of the turn; a tighter corner brings the rear wheels further inside the path of the front wheels.
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42. An angry driver has cut in front of you and is now braking hard to provoke you. What is the safest response?
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Answer D: Drop back, avoid eye contact and let the driver go
Giving an aggressive driver space and no response removes the conflict, while any answering gesture invites escalation you cannot control in a heavy vehicle.
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43. What extinguisher rating is required on a vehicle carrying hazardous materials in amounts that need placards?
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Answer B: 10 B:C or more
Placarded loads carry a much higher fire risk, so the required extinguisher rating rises to at least 10 B:C.
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44. What are you checking on the mud flaps during the walkaround?
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Answer C: That they are securely attached, not torn and not dragging on the ground
A flap that is torn or hanging loose stops shielding following traffic from spray and stones, and a dragging flap can catch and tear away on the road.
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45. What is the purpose of an escape ramp on a mountain grade?
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Answer C: To stop a runaway vehicle without injuring the driver
Escape ramps use soft material or a steep upgrade to bring a vehicle with failed brakes to a controlled stop.
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46. Which exhaust system condition must be reported as a defect?
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Answer B: A section repaired by wrapping tape or patching material around the pipe
Exhaust parts may not be patched with wrap or tape, because the repair does not contain the gas or the heat and it fails quickly in service.
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47. An oncoming vehicle drifts across the center line into your lane. What is usually the safest move?
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Answer C: Steer to the right, toward the shoulder if necessary
Moving right keeps you away from the drifting vehicle and off the oncoming side; the other driver may swerve back and hit you if you go left.
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48. How soon must warning devices be placed after a commercial vehicle stops on the traveled part or the shoulder of a highway?
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Answer D: As soon as possible and in any case within 10 minutes
The hazard warning flashers go on immediately and the warning devices must be in place as soon as possible, never later than 10 minutes after stopping.
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49. What are you looking for when you check the hubs and wheel seals during the walkaround?
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Answer B: Leaking oil or grease, which can also contaminate the brake linings
A leaking hub seal starves the bearing of lubricant and the escaping oil or grease can soak the brake linings and cut braking power.
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50. What must the driver check about the seat belt during the inspection?
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Answer A: That it is securely mounted, adjusts properly and is not ripped or frayed
A belt only restrains the driver if its anchorage is sound and the webbing is intact, so mounting and condition are both checked.