How do I get a CDL in South Carolina?

Pass the written knowledge tests for the class and endorsements you want, hold a commercial learner's permit for at least 14 days, complete federal Entry-Level Driver Training, then pass the skills test. South Carolina's licensing agency publishes the current fees and appointment rules.

How many questions are on the South Carolina CDL General Knowledge test?

50, with 80% correct to pass. Air Brakes adds 25 questions and Combination Vehicles 20.

Are CDL rules the same in every state?

The core knowledge is federal — 49 CFR and the AAMVA model manual — so the questions barely change across state lines. Fees, waiting periods and endorsement details are set by the state.

Why does an air-braked vehicle have a delay between pressing the brake pedal and the brakes actually working, a delay that a car with hydraulic brakes does not have?

The compressed air needs time to travel down the lines and reach the brake chambers

The air compressor must first pump the tanks back up to governor cut-out pressure

The spring brakes must fully release before the service brakes can be applied

Which observation points specifically at a driver who may be sleepy, ill, or under the influence, rather than at some other kind of hazard?

A side window down in freezing weather, together with the car wandering from one side of its lane to the other

Roof-rack luggage and out-of-state plates on a car that keeps slowing near interchanges

A raised hood and a jacked-up wheel on a car sitting on the shoulder

An inspector places a truck out of service for defective brakes. The driver moves it five miles to a repair shop anyway. It is his first such incident. What is the minimum disqualification?

None, because he was driving to have the defect repaired

Which of these is prohibited hand-held mobile telephone use while driving a CMV?

Moving out of the seated, belted driving position to reach for the phone, even if you meant to use it hands-free

Talking through an earpiece connected to a phone mounted within reach

Pressing a single button on a phone already within close reach to answer a call

What is traction, and why does it govern how fast you can safely drive?

The grip a tire finds against the road surface, which every steering and braking input has to draw on

The pulling power the engine sends to the drive axle, which is what gets a loaded vehicle up a grade

The bite of the linings against the drums, which is what actually slows the turning wheels

When must you dim your high beams at night?

Within 500 feet of an oncoming vehicle, and also when you are following another vehicle within 500 feet

Only after an oncoming driver flashes their lights at you

Only within 500 feet of an oncoming vehicle

What is the tractor protection valve for?

Sealing the tractor's own air in if the trailer separates or springs a serious leak

Keeping the trailer tanks from filling above the governor's cut-out pressure

Holding the trailer's spring brakes released while the rig is parked

In an emergency stop, under what condition may a driver simply push the brake pedal all the way down and hold it?

Only when every axle of the vehicle, or of the entire combination, carries a functioning antilock system

Any time the road surface is dry, regardless of the vehicle's equipment

Only when the vehicle is empty, because a light vehicle cannot lock its wheels

A driver crosses state lines both for excepted activities and, at other times, for ordinary commercial hauling. Which status must he certify to?

Non-excepted interstate, so that he is qualified for both kinds of interstate driving

Excepted interstate, because he performs excepted activities at least part of the time

He may choose either status and switch whichever way suits each trip

A driver never leaves his own state, but the freight he hauls arrived from another state and he carries it on the last leg of that journey. How is this operation classified?

Interstate commerce, because the cargo is part of a trip that began in another state

Intrastate commerce, because the truck itself never crosses a state line

Neither, because classification depends only on where the carrier is based

Which combination makes hydroplaning most likely?

Water lying on the road plus soft tires or shallow tread, which can start it near 30 mph

Any speed above 55 mph, whatever condition the tires happen to be in

Deep water on its own; inflation and tread depth have no bearing on it

How do you verify that the parking brake will actually hold the vehicle?

With your safety belt fastened and the brake set, select a low gear and pull gently forward against it.

Set it, shut the engine off, and confirm the dash indicator stays lit.

Set it on level ground and confirm the vehicle does not roll when you release the service brake.

South Carolina CDL Practice Test 2026

Free South Carolina CDL practice test: General Knowledge, Air Brakes and Combination Vehicles questions written from the official CDL manuals, each with an explanation.

The three knowledge tests

Practice questions

20 questions, answered right here. Tap an option to see why.

0 of 20 answeredScore: 0/2016 to pass

1.
Why does an air-braked vehicle have a delay between pressing the brake pedal and the brakes actually working, a delay that a car with hydraulic brakes does not have?
Not quiteCorrect answer: A — The compressed air needs time to travel down the lines and reach the brake chambers
Hydraulic fluid is nearly incompressible, so a car's brakes bite as soon as the pedal moves. Air is compressible and has to flow through long lines before it can push the chamber pushrods, and that transit time is why roughly half a second or more passes before braking force appears.
Believing brake lag is caused by the compressor or by low tank pressure, so a driver assumes a full, healthy air system means there is no lag at all.
2.
Which observation points specifically at a driver who may be sleepy, ill, or under the influence, rather than at some other kind of hazard?
Not quiteCorrect answer: C — A side window down in freezing weather, together with the car wandering from one side of its lane to the other
Cold air on the face is a common self-treatment for drowsiness, and wandering inside the lane says the lane-keeping job has already degraded. Both point at the driver's condition rather than at circumstances.
Filing every roadside oddity under one heading called 'hazard'. Each clue predicts a different next move, and a driver who does not separate them never forms the specific expectation that matters: that the impaired car may drift into your lane, that the unfamiliar driver may brake or turn without warning, that someone may step out from behind the raised hood.
3.
An inspector places a truck out of service for defective brakes. The driver moves it five miles to a repair shop anyway. It is his first such incident. What is the minimum disqualification?
Not quiteCorrect answer: B — At least 90 days
An out-of-service order means the vehicle or driver stops moving, and driving in defiance of it is the violation regardless of the destination. Even a first offense costs at least 90 days.
The belief that a good reason for moving, such as heading for repairs, excuses driving under an out-of-service order.
4.
Which of these is prohibited hand-held mobile telephone use while driving a CMV?
Not quiteCorrect answer: C — Moving out of the seated, belted driving position to reach for the phone, even if you meant to use it hands-free
The federal restriction names three acts: holding the phone with at least one hand for a voice call, dialing by pressing more than a single button, and moving out of the belted driving position to reach for it. That last one stands on its own, regardless of what you planned to do once you had the phone.
The 'as long as I never hold it to my ear I'm compliant' rule of thumb. It ignores the reach itself, which is exactly the moment the driver is unbelted, twisted, and not looking at the road.
5.
What is traction, and why does it govern how fast you can safely drive?
Not quiteCorrect answer: A — The grip a tire finds against the road surface, which every steering and braking input has to draw on
Steering and braking are both requests made through the tire contact patch, and the road has to be able to answer them. When a surface cuts the available friction, every input you make gets weaker, so the only remaining control you have is speed.
Confusing traction with engine pulling power or with brake friction. A driver who thinks traction lives in the drivetrain or the brake drums will look for the problem inside the vehicle instead of at the road surface, and will keep speed up on a slick road because the truck still feels strong.
6.
When must you dim your high beams at night?
Not quiteCorrect answer: A — Within 500 feet of an oncoming vehicle, and also when you are following another vehicle within 500 feet
Your beams reach a driver ahead of you through their mirrors just as they reach an oncoming driver through the windshield. Both situations blind someone, so both call for low beams.
Thinking high beams only bother oncoming traffic. The driver you are following gets the glare bounced straight into their eyes from two mirrors, and they are the one directly in front of your bumper.
7.
What is the tractor protection valve for?
Not quiteCorrect answer: C — Sealing the tractor's own air in if the trailer separates or springs a serious leak
Without it, a torn trailer hose would empty the whole system and leave the tractor with no service brakes at all. It seals the tractor's air in, and in doing so it vents the trailer emergency line, which sets the trailer's emergency brakes.
Thinking the valve protects the trailer. It protects the powered unit's air supply, and the trailer's emergency brakes coming on is a consequence of that, not its purpose.
8.
In an emergency stop, under what condition may a driver simply push the brake pedal all the way down and hold it?
Not quiteCorrect answer: C — Only when every axle of the vehicle, or of the entire combination, carries a functioning antilock system
Full pedal is safe only when every wheel has a system preventing it from locking. With antilock protection working everywhere, the computer holds the wheels short of lockup; anywhere else, mashing the pedal locks wheels and costs steering.
The belief that an emergency always justifies standing on the pedal, and the related error that dry pavement or a light load makes lockup impossible. Empty rigs actually lock up more easily.
9.
A driver crosses state lines both for excepted activities and, at other times, for ordinary commercial hauling. Which status must he certify to?
Not quiteCorrect answer: C — Non-excepted interstate, so that he is qualified for both kinds of interstate driving
Excepted status only holds when the excepted activities are all the driver does. As soon as any ordinary interstate work is mixed in, the stricter certification is the only one that keeps him legal across the whole range of his driving.
Believing that qualifying for an exception in part of your work extends the exception to the rest of it.
10.
A driver never leaves his own state, but the freight he hauls arrived from another state and he carries it on the last leg of that journey. How is this operation classified?
Not quiteCorrect answer: B — Interstate commerce, because the cargo is part of a trip that began in another state
The test follows the journey of the freight, not the odometer of one truck. A load that started or will finish in another state keeps its interstate character through every leg, including a purely local final run.
The widespread belief that staying inside state lines automatically makes a driver an intrastate operator, which leads drivers to self-certify wrongly and skip the federal medical certificate.
11.
Which combination makes hydroplaning most likely?
Not quiteCorrect answer: B — Water lying on the road plus soft tires or shallow tread, which can start it near 30 mph
A tire clears water through its tread grooves; shallow grooves move less of it, and an underinflated tire changes the shape of the contact patch so it clears less still. With enough water down, that failure can begin around 30 mph, nowhere near highway speed.
Filing hydroplaning as a high-speed-only hazard, which lets a driver feel safe at moderate speed on a flooded surface. It also hides the part the driver actually controls: tread depth and inflation are checked in the pre-trip, long before the rain starts.
12.
How do you verify that the parking brake will actually hold the vehicle?
Not quiteCorrect answer: A — With your safety belt fastened and the brake set, select a low gear and pull gently forward against it.
Only applying load proves holding force. Gently pulling against the set brake asks the question that matters, whether it will hold this vehicle at this weight, which no indicator lamp and no level surface can answer.
Confirming that the brake is applied instead of confirming that it holds. Contaminated shoes or slack adjustment will show 'set' on the dash and still let a loaded vehicle walk away on a grade.
13.
You are braking to a stop in a truck with a manual transmission. When should the clutch pedal go in?
Not quiteCorrect answer: B — Once engine speed has dropped close to idle
Holding the clutch out while the engine is still turning above idle keeps the driveline connected, so the engine helps slow the vehicle and you keep the ability to power out of trouble. Disconnecting it only at the point where the engine would otherwise stall gives you that benefit without stalling.
The habit of pushing the clutch in as soon as braking starts, or coasting out of gear. A disconnected driveline throws away engine braking and leaves the brakes to do all of the work of a heavy vehicle alone.
14.
On a typical tractor or straight truck, the spring brakes come fully on when air pressure falls to about:
Not quiteCorrect answer: B — 20 to 45 psi
The springs take over well below the warning threshold, most often somewhere in the twenties or thirties. That gap exists so a driver who reacts to the warning can park deliberately rather than being stopped by the vehicle.
Believing the spring brakes apply at the same pressure that triggers the warning light, which would leave no reaction time at all.
15.
Which statement about blind spots on a large vehicle is correct?
Not quiteCorrect answer: A — Blind spots remain however the mirrors are set, so you check often enough to know when a vehicle has gone into one
No mirror arrangement covers every area around a long vehicle. What frequent checking gives you is continuity: you saw the vehicle approach, you know roughly where it must be now, and you know not to move over even though the glass currently shows nothing there.
Reading an empty mirror as an empty lane. A blind spot is defined by not appearing in any mirror, so the absence of a vehicle in the glass is not evidence that the lane is clear.
16.
You have to back into a loading area you have never used before. What should you do before the vehicle moves?
Not quiteCorrect answer: B — Get out first and walk the line the vehicle will take, looking at what is beside it and what is above it
Walking the route is the only way to learn what is actually there: low obstructions, soft ground, overhead wires, canopies, and objects that sit entirely inside your blind area. Once you are back in the seat, that knowledge is what you steer by, because the mirrors will not supply it.
Believing convex mirrors eliminate blind spots. They widen the view and shrink everything in it; they do not show the ground immediately behind the vehicle or anything above the roof line.
17.
A driver hauls a full load out in the morning and drives the same route back with an empty trailer. What should the driver expect on the return trip?
Not quiteCorrect answer: A — It will need more room to stop, because less weight is pressing the tires onto the road
The running gear and suspension of a heavy vehicle are built around the weight it is meant to carry, and they behave best when that weight is actually on board. Take the load away and the tires press into the surface far less firmly, grip falls off, wheels lock more readily, and the empty unit ends up needing more road than the loaded one did.
The intuition that lighter always means shorter stops. It is true that a heavier vehicle asks more work of the brakes, but a driver who reasons from weight alone will run an empty rig at loaded-vehicle following distances and be caught short.
18.
Why does jerky, abrupt acceleration matter in a tractor-trailer, beyond making the ride uncomfortable?
Not quiteCorrect answer: C — It can break things mechanically, the coupling that holds a trailer to the tractor included
Every sudden surge of torque is absorbed as shock loading by the drivetrain and, when a trailer is behind you, by the coupling that transmits the pull. Building speed smoothly spreads that load out over time instead of hammering the hardware that holds the combination together.
Thinking of smooth acceleration purely as a comfort or fuel-economy habit. In a combination vehicle it is a mechanical-integrity issue affecting the parts that keep the trailer attached.
19.
You find a wheel that has been repaired by welding. How should it be treated?
Not quiteCorrect answer: A — As unsafe: a welded wheel or rim should not be put back on the road.
A rim carries the full dynamic load of the vehicle through a rotating, heat-cycled part. Welding changes the metal around the repair, and that heat-affected zone is where the wheel will crack under load.
Thinking of a wheel as a bracket that can be welded and put back to work, when a rim failure at speed is a wheel-off event rather than a repairable inconvenience.
20.
Your dispatcher tells you to answer the phone by hand while you are rolling, because loads are running late. What is the correct understanding of this situation?
Not quiteCorrect answer: B — Carriers are barred from requiring or allowing hand-held use, so the instruction is improper and exposes the carrier to its own penalties, but the violation and any resulting disqualification still land on you
The prohibition runs in both directions: carriers must not require or allow it, and employers can face civil penalties up to $11,000, while the driver's own violations still carry penalties and count toward disqualification. Nothing in the rule lets an order transfer the driver's exposure.
The belief that an employer's instruction shifts liability off the driver. It does not, and the driver who takes that on faith is the one whose CDL is disqualified after the second conviction.

Questions people ask

How do I get a CDL in South Carolina?: Pass the written knowledge tests for the class and endorsements you want, hold a commercial learner's permit for at least 14 days, complete federal Entry-Level Driver Training, then pass the skills test. South Carolina's licensing agency publishes the current fees and appointment rules.
How many questions are on the South Carolina CDL General Knowledge test?: 50, with 80% correct to pass. Air Brakes adds 25 questions and Combination Vehicles 20.
Are CDL rules the same in every state?: The core knowledge is federal — 49 CFR and the AAMVA model manual — so the questions barely change across state lines. Fees, waiting periods and endorsement details are set by the state.

Where this comes from

49 CFR Part 383 — Commercial Driver's License Standards; Requirements and Penalties — U.S. Federal Motor Carrier Safety Administration
49 CFR Part 392 — Driving of Commercial Motor Vehicles — U.S. Federal Motor Carrier Safety Administration
49 CFR Part 393 — Parts and Accessories Necessary for Safe Operation — U.S. Federal Motor Carrier Safety Administration
49 CFR Part 395 — Hours of Service of Drivers — U.S. Federal Motor Carrier Safety Administration
49 CFR Part 396 — Inspection, Repair, and Maintenance — U.S. Federal Motor Carrier Safety Administration
Commercial Driver's License Manual (AAMVA Modernized Testing System), 2026 edition published by the Virginia DMV — American Association of Motor Vehicle Administrators / Virginia DMV
New York State Commercial Driver's Manual — English (CDL-10) and official Spanish edition (CDL-10S) — New York State DMV
Manual on Uniform Traffic Control Devices (MUTCD), 11th Edition — U.S. Federal Highway Administration

Independent study aid. Not affiliated with, endorsed by or connected to any Department of Motor Vehicles or government agency. Questions are written from the official handbooks listed above; no exam result is guaranteed.

The three knowledge tests

Practice questions

Why does an air-braked vehicle have a delay between pressing the brake pedal and the brakes actually working, a delay that a car with hydraulic brakes does not have?

Which observation points specifically at a driver who may be sleepy, ill, or under the influence, rather than at some other kind of hazard?

An inspector places a truck out of service for defective brakes. The driver moves it five miles to a repair shop anyway. It is his first such incident. What is the minimum disqualification?

Which of these is prohibited hand-held mobile telephone use while driving a CMV?

What is traction, and why does it govern how fast you can safely drive?

When must you dim your high beams at night?

What is the tractor protection valve for?

In an emergency stop, under what condition may a driver simply push the brake pedal all the way down and hold it?

A driver crosses state lines both for excepted activities and, at other times, for ordinary commercial hauling. Which status must he certify to?

A driver never leaves his own state, but the freight he hauls arrived from another state and he carries it on the last leg of that journey. How is this operation classified?

Which combination makes hydroplaning most likely?

How do you verify that the parking brake will actually hold the vehicle?

You are braking to a stop in a truck with a manual transmission. When should the clutch pedal go in?

On a typical tractor or straight truck, the spring brakes come fully on when air pressure falls to about:

Which statement about blind spots on a large vehicle is correct?

You have to back into a loading area you have never used before. What should you do before the vehicle moves?

A driver hauls a full load out in the morning and drives the same route back with an empty trailer. What should the driver expect on the return trip?

Why does jerky, abrupt acceleration matter in a tractor-trailer, beyond making the ride uncomfortable?

You find a wheel that has been repaired by welding. How should it be treated?

Your dispatcher tells you to answer the phone by hand while you are rolling, because loads are running late. What is the correct understanding of this situation?

Questions people ask

CDL practice by state

Where this comes from