South Carolina CDL — General Knowledge Practice Test
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South Carolina CDL — General Knowledge questions with answers
20 sample questions from the South Carolina CDL — General Knowledge question bank — each with the correct answer, a short explanation, and the section of the official handbook it comes from.
1. How do you stop a front-wheel skid?
Correct answer: Let the vehicle slow down by easing off turning and braking
In a front-wheel skid the only way to stop it is to let the vehicle slow down by stopping hard turning or braking.
Source: South Carolina CDL Manual — Section 2: Driving Safely (Front-wheel Skids)
2. Which of these counts as a serious traffic violation for a CDL holder?
Correct answer: Speeding 15 mph or more above the limit
Excessive speeding of 15 mph or more over the posted limit is one of the serious traffic violations, along with reckless driving and following too closely.
Source: South Carolina CDL Manual — Section 1: Introduction (Serious Traffic Violations)
3. Before you change lanes, what should you do to communicate the move?
Correct answer: Turn on your signal before beginning the lane change
Put on your turn signal before you change lanes, and make the change slowly and smoothly.
Source: South Carolina CDL Manual — Section 2: Driving Safely (Lane Changes)
4. What is the only real cure for driver fatigue?
Correct answer: Stopping to sleep
The only safe cure for being drowsy is to get off the road and sleep; coffee and fresh air are not real fixes.
Source: South Carolina CDL Manual — Section 2: Driving Safely (If You Get Sleepy)
5. A hazardous-materials placard is shaped and mounted in what way on the outside of a vehicle?
Correct answer: A square turned to a point so it reads as a diamond
Placards are square signs turned to stand on a point, forming a diamond, and must be readable from all four sides of the vehicle.
Source: South Carolina CDL Manual — Section 2: Driving Safely (Lists of Regulated Products)
6. How does the speed at which a person drinks affect their blood alcohol concentration?
Correct answer: Faster drinking raises the BAC
Drinking faster produces a higher BAC, because alcohol builds up when you consume it faster than your body can clear it.
Source: South Carolina CDL Manual — Section 2: Driving Safely (What Determines Blood Alcohol Concentration?)
7. How is road rage different from aggressive driving?
Correct answer: Road rage involves intending to harm or assault someone
Road rage is operating a vehicle with the intent to harm others or physically assault a driver or their vehicle, going beyond mere aggressive driving.
Source: South Carolina CDL Manual — Section 2: Driving Safely (What Is It?)
8. At a flashing-light crossing with more than one track, what must you confirm before you cross?
Correct answer: That all of the tracks are clear
If several tracks are present, confirm each is clear before crossing, since a train on the first rails can conceal one on the next.
Source: South Carolina CDL Manual — Section 2: Driving Safely (Flashing Red Light Signals)
9. On packed snow, by about how much should you reduce your speed?
Correct answer: By about half or more
On packed snow you should cut your speed by about half or more.
Source: South Carolina CDL Manual — Section 2: Driving Safely (Slippery Surfaces)
10. At a crossing with a painted white stop line, where must the front of a school bus remain while stopped?
Correct answer: Behind the painted stop line
The front of the school bus must stay behind the white stop line painted before the tracks while it is stopped at the crossing.
Source: South Carolina CDL Manual — Section 2: Driving Safely (Pavement Markings)
11. Under the state hands-free act, what does the law say about viewing moving images such as videos or video calls while driving?
Correct answer: It is prohibited while driving
The act forbids watching moving images, including videos, movies, games, or video calls, while operating a vehicle on a public road.
Source: South Carolina CDL Manual — Section 2: Driving Safely (South Carolina Hands-Free and Distracted Act)
12. If your engine catches fire, what should you avoid doing?
Correct answer: Opening the hood to reach the flames
Turn off the engine and avoid opening the hood if you can, since opening it feeds the fire more oxygen.
Source: South Carolina CDL Manual — Section 2: Driving Safely (Keep the Fire from Spreading)
13. What is the CDL disqualification for a first railroad-highway grade crossing violation?
Correct answer: At least 60 days
A first grade-crossing violation results in losing your CDL for at least 60 days.
Source: South Carolina CDL Manual — Section 1: Introduction (Railroad-highway Grade Crossing Violations)
14. South Carolina law (Code 56-5-4780) sets a minimum distance for dimming your headlights when approaching another vehicle from behind. What is that minimum?
Correct answer: 200 feet
State law requires you to dim your headlights within at least 200 feet when coming up behind another vehicle.
Source: South Carolina CDL Manual — Section 2: Driving Safely (Avoid Blinding Others)
15. Why does the manual warn about the space beneath your vehicle at railroad tracks and drainage channels?
Correct answer: The vehicle could drag or get hung up on the surface
Ground clearance can be very small when heavily loaded, and tracks or drainage dips can make the ends of the vehicle drag or hang up.
Source: South Carolina CDL Manual — Section 2: Driving Safely (Space Below)
16. Besides the pavement 'X' and 'RR' letters, what other marking appears on a two-lane road ahead of a railroad crossing?
Correct answer: A no-passing zone marking
On a two-lane road the crossing markings also include a no-passing zone marking, and a no-passing sign may be posted as well.
Source: South Carolina CDL Manual — Section 2: Driving Safely (Pavement Markings)
17. Why does a smaller person generally reach a given blood alcohol concentration on less alcohol?
Correct answer: Because weight affects how much alcohol is needed to reach a BAC
Body weight affects BAC, so a small person does not have to drink as much as a larger one to reach the same concentration.
Source: South Carolina CDL Manual — Section 2: Driving Safely (What Determines Blood Alcohol Concentration?)
18. How does the manual describe aggressive driving?
Correct answer: Driving in a selfish and pushy way that ignores others' safety
The manual describes aggressive driving as operating a vehicle selfishly, boldly, or pushily with no concern for others' rights or safety.
Source: South Carolina CDL Manual — Section 2: Driving Safely (Aggressive Drivers/Road Rage)
19. If there are two left-turn lanes, which one should a commercial driver use?
Correct answer: The right-hand of the two turn lanes
Use the right-hand turn lane; starting in the inside lane may force you to swing right and endanger drivers on your left.
Source: South Carolina CDL Manual — Section 2: Driving Safely (Left Turns)
20. At what speed can hydroplaning begin if there is a lot of water on the road?
Correct answer: As low as 30 mph
When plenty of water covers the road, a vehicle can begin to hydroplane at speeds down around 30 mph.
Source: South Carolina CDL Manual — Section 2: Driving Safely (Hydroplaning)