Commercial Driver's License (CDL) General Knowledge — Questions and Answers

Question 1: You are driving a 40 foot truck at 35 MPH, how much space (in seconds) should you keep in front of you?

6 seconds
3 seconds
5 seconds
4 seconds (Correct answer)

Correct answer: 4 seconds

The standard rule for commercial vehicles is to maintain a following distance of at least one second for every 10 feet of vehicle length. For a 40-foot truck, this calculation yields 4 seconds (40 feet / 10 feet per second). Since the speed is 35 MPH (not exceeding 40 MPH), no additional second is required, making 4 seconds the correct safe following distance.

Question 2: What does Class 8 in the hazardous materials classification system represent?

Flammable solids
Oxidizers
Corrosives (Correct answer)
Gases

Correct answer: Corrosives

Class 8 covers corrosive materials such as strong acids and bases that can damage skin and metal.

Question 3: What is 'rearward amplification' in a combination vehicle?

The increase in stopping distance caused by the rear trailer brakes applying last
The magnification of sway toward the rear of a combination, so the last trailer swings more violently than the tractor (Correct answer)
The tendency of the trailer to track wider than the tractor on highway curves
The buildup of air pressure delay from the tractor to the rearmost trailer axle

Correct answer: The magnification of sway toward the rear of a combination, so the last trailer swings more violently than the tractor

Rearward amplification means that a lane-change or swerving motion grows progressively larger toward the rear of the vehicle. A triple-trailer combination can see the last trailer sway several times more than the tractor, making rollovers or loss of control far more likely at highway speeds.

Question 4: When parking and uncoupling a trailer on soft ground, what should you place under the landing gear?

Plates or blocks to support it (Correct answer)
The tractor's spare tire
The trailer air hoses
Nothing, the gear is self-supporting

Correct answer: Plates or blocks to support it

Soft surfaces can let the landing gear sink, so support it with plates or blocks.

Question 5: While driving a bus, how many feet before a railroad crossing should you stop?

150 to 175 ft.
125 to 150 ft.
75 to 100 ft.
15 to 50 ft. (Correct answer)

Correct answer: 15 to 50 ft.

Federal regulations and CDL guidelines mandate that commercial vehicles, including buses, stop at railroad crossings. The required stopping distance is between 15 and 50 feet from the nearest rail. This range provides sufficient space to clear the tracks if another vehicle stops behind, while also allowing the driver a clear view of the tracks in both directions for safety.

Question 6: Who is responsible for making sure cargo is properly secured and the vehicle is not overloaded?

Only the shipper
Only the carrier's dispatcher
The driver (Correct answer)
Only the loading dock crew

Correct answer: The driver

Regardless of who loaded it, the driver is responsible for inspecting the cargo and making sure it is secure and within legal weight limits.

Question 7: What is another term for a brake pedal?

S-cam
Treadle valve (Correct answer)
Wedge brake
Brake shoe

Correct answer: Treadle valve

Treadle valve. A brake pedal can also be known as a treadle valve or a foot valve.

Question 8: What is the purpose of blocking and bracing cargo?

To reduce the total weight on the axles
To prevent cargo from sliding or shifting (Correct answer)
To raise the center of gravity for better traction
To keep cargo dry

Correct answer: To prevent cargo from sliding or shifting

Blocking and bracing fit against the cargo to stop it from moving forward, backward, or sideways.

Question 9: A tiedown is made of a chain, a binder, and a hook with different working load limits. What is the WLL of the whole assembly?

The rating of the weakest component (Correct answer)
The sum of all component ratings
The rating of the chain only
The average of the component ratings

Correct answer: The rating of the weakest component

A tiedown assembly is only as strong as its lowest-rated component.

Question 10: Which of the following devices can be used as the low air pressure warning signal?

Red warning light
A mechanical arm (wig wag)
A buzzer
Any of the above (Correct answer)

Correct answer: Any of the above

Federal regulations require commercial vehicles with air brakes to have a low air pressure warning signal to alert the driver when system pressure drops below 60 psi. This critical warning can be provided by various means, including an audible buzzer, a visual red warning light, or a mechanical arm known as a 'wig-wag.' All these devices serve the same essential safety function.

Question 11: What should the combined working load limit of all tiedowns be, at minimum?

One-half of the cargo weight (Correct answer)
Equal to the cargo weight
Twice the cargo weight
One-quarter of the cargo weight

Correct answer: One-half of the cargo weight

The aggregate working load limit of all tiedowns must be at least one-half the weight of the cargo being secured.

Question 12: Which of the following is the most common type of foundation brake?

Disc brake
Anti-lock brake
Wedge brake
S-cam drum brake (Correct answer)

Correct answer: S-cam drum brake

The S-cam drum brake is the most prevalent type of foundation brake found on heavy-duty commercial vehicles. When air pressure is applied, the S-cam rotates, forcing the brake shoes against the inside of the brake drum, creating friction to slow or stop the vehicle. Its robust and reliable design makes it ideal for commercial applications.

Question 13: When is it acceptable to not use parking brakes if you have to leave your vehicle unattended?

If you are on a flat road surface
If you will only be gone a short time
If your wheels are turned at a harsh angle
You should never leave your vehicle without using parking brakes or chocking the wheels (Correct answer)

Correct answer: You should never leave your vehicle without using parking brakes or chocking the wheels

You should never leave your vehicle without using parking brakes or chocking the wheels. If you leave your vehicle unattended without the parking brakes on or the wheels chocked, the vehicle might roll away.

Question 14: What emergency equipment is required to be carried in a commercial vehicle under federal regulations?

Three reflective triangles or flares, a fire extinguisher, and spare electrical fuses (Correct answer)
Only a first aid kit and fire extinguisher
Just a fire extinguisher and jumper cables
Only a fire extinguisher

Correct answer: Three reflective triangles or flares, a fire extinguisher, and spare electrical fuses

Federal regulations require at minimum three reflective triangles (or equivalent warning devices), a properly rated fire extinguisher, and spare electrical fuses.

Question 15: A combustible liquid has a flash point of:

At or above 141°F and below 200°F (Correct answer)
Between 73°F and 100°F
Above 300°F
Below 73°F

Correct answer: At or above 141°F and below 200°F

Combustible liquids have flash points at or above 141°F and below 200°F.

Question 16: What should you inspect when checking the steering mechanism during a pre-trip inspection?

Only that the wheel turns left and right
Only confirm the steering wheel is attached
Excessive play, loose or missing nuts, and bent or damaged components (Correct answer)
Steering is only inspected after a collision

Correct answer: Excessive play, loose or missing nuts, and bent or damaged components

A proper steering check includes inspecting for excessive play (no more than 10 degrees of free movement) and checking for damaged, loose, or missing components.

Question 17: A driver of a placarded vehicle approaching a railroad crossing must:

Stop only if a train is visible
Slow and shift gears over the tracks
Stop, listen and look, then proceed when clear (Correct answer)
Sound the horn and continue

Correct answer: Stop, listen and look, then proceed when clear

Placarded vehicles must stop 15 to 50 feet from the nearest rail and look and listen before crossing.

Question 18: What are the three types of brake systems used in a commercial vehicle air brake system?

Service brake, hand brake, emergency brake
Service brake, parking brake, emergency brake (Correct answer)
Hand brake, parking brake, emergency brake
Anti-lock brake, service brake, emergency brake

Correct answer: Service brake, parking brake, emergency brake

Commercial vehicles with air brakes utilize three distinct braking systems. The service brake is used for normal stopping, the parking brake holds the vehicle stationary when parked, and the emergency brake system uses parts of the service and parking brake systems to stop the vehicle in case of a service brake failure. These systems work together to ensure safe operation and parking.

Question 19: Why should you NOT use the trailer hand brake to hold the vehicle while parked?

Air may leak away and release the brakes, or brakes may freeze in cold weather (Correct answer)
It will damage the kingpin
It is illegal in every state
It disables the tractor parking brake permanently

Correct answer: Air may leak away and release the brakes, or brakes may freeze in cold weather

Air can leak and release the trailer brakes, so use the parking brakes and wheel chocks instead.

Question 20: You will be denied or lose your hazardous materials endorsement, if you _______.

If you are under indictment for certain felonies.
All of the listed answers. (Correct answer)
Have a conviction in military or civilian court for certain felonies.
Have been committed to a mental institution.

Correct answer: All of the listed answers.

A hazardous materials endorsement (HME) is subject to strict security requirements due to the inherent risks of transporting dangerous goods. Drivers will be denied or lose their HME if they have certain felony convictions (military or civilian), are under indictment for specific felonies, or have been committed to a mental institution. These measures ensure only responsible individuals handle hazardous materials.

Question 21: When testing the air governor cut-in and cut-out, at what approximate pressure should the compressor cut out?

Around 85 psi
Around 60 psi
Around 200 psi
Around 125 psi (Correct answer)

Correct answer: Around 125 psi

Compressors typically cut out near 125 psi and cut in around 100 psi.

Question 22: At what pressure must the low-air warning device activate?

Before pressure drops below 60 psi (Correct answer)
Before pressure drops below 40 psi
Before pressure drops below 80 psi
Before pressure drops below 20 psi

Correct answer: Before pressure drops below 60 psi

The low-air warning signal must come on before pressure falls below 60 psi in the tank.

Question 23: A truck has an engine manufactured before model year 2000. What is its ELD status?

It is exempt from all hours-of-service rules
It is exempt from the ELD requirement but the driver still keeps paper logs (Correct answer)
It may use an AOBRD indefinitely
It must install an ELD with an adapter

Correct answer: It is exempt from the ELD requirement but the driver still keeps paper logs

Vehicles with pre-2000 engines are exempt from ELDs, but drivers must still record duty status on paper logs if required.

Question 24: What is rearward amplification?

'Crack-the-whip' effect when making quick lane changes (Correct answer)
Weight transfer to the rear axles when going up a hill in a double/triple
Sudden, dangerous weight shift from the front to the rear trailer
The increased weight on the rear axles of a double or triple trailer

Correct answer: 'Crack-the-whip' effect when making quick lane changes

Rearward amplification, also known as the 'crack-the-whip' effect, describes how quick steering movements can be amplified down a set of multiple trailers. The last trailer in a double or triple combination will swing out much wider and with greater force than the tractor. This effect makes quick lane changes or sudden maneuvers extremely dangerous with multiple trailers.

Question 25: On a combination vehicle with air brakes, the trailer air supply (yellow) valve should pop out automatically when air pressure drops to about what range?

20 to 45 psi (Correct answer)
60 to 80 psi
90 to 100 psi
5 to 10 psi

Correct answer: 20 to 45 psi

The trailer supply valve closes at roughly 20 to 45 psi, applying the trailer emergency brakes.

Question 26: Which of the following devices indicates how much air pressure you are applying to your brakes?

Governor
Application pressure gauge (Correct answer)
Supply pressure gauge
Low air pressure warning signal

Correct answer: Application pressure gauge

The application pressure gauge indicates how much air pressure is being sent to the brake chambers when the driver presses the brake pedal. This gauge helps the driver monitor their braking effort and ensures that the brakes are receiving adequate pressure for effective stopping. It is distinct from the supply pressure gauge, which shows the total air pressure available in the tanks.

Question 27: Cargo securement systems must be able to withstand forward deceleration forces of at least what fraction of the cargo's weight?

1.5 g
0.2 g
0.5 g
0.8 g (Correct answer)

Correct answer: 0.8 g

Performance criteria require resisting 0.8 g forward deceleration, which is the highest of the required forces.

Question 28: You are hauling a sealed trailer you cannot open. What are you still responsible for?

Re-sealing the trailer at every stop
Nothing, since the shipper sealed it
Making sure you do not exceed gross and axle weight limits (Correct answer)
Breaking the seal to inspect the load

Correct answer: Making sure you do not exceed gross and axle weight limits

Even with a sealed load you cannot inspect, you must ensure the vehicle is not over gross or axle weight limits.

Question 29: What should you do if a trailer's air supply valve is in the 'emergency' position during a pre-trip inspection?

Push it in to restore air supply before moving the vehicle (Correct answer)
Leave it as-is; the emergency position is normal for parked trailers
Disconnect the air lines and reconnect them to reset the valve
Connect a portable air tank and drive slowly to a service center

Correct answer: Push it in to restore air supply before moving the vehicle

When the trailer air supply valve (sometimes called the tractor protection valve) is in the emergency position, air is cut off to the trailer and the trailer spring brakes are applied. You must push it to the normal position to supply air and release the brakes before driving.

Question 30: What does this white, rectangular sign with black lettering tell you?

Due to road conditions, passing is not recommended.
Road closed unless you have an off-road vehicle.
Road is closed during night hours.
Road closed to all vehicles. (Correct answer)

Correct answer: Road closed to all vehicles.

White rectangular signs are regulatory signs that provide specific instructions or prohibitions. A 'ROAD CLOSED' sign explicitly indicates that the road ahead is impassable and closed to all vehicles, usually due to construction, hazards, or emergencies. Drivers must find an alternative route.

Question 31: What is the purpose of a converter dolly in a double or triple combination?

It provides extra braking power for the rear trailers
It houses the air tanks for the rear trailer's braking system
It converts the lead trailer's kingpin into a fifth-wheel coupling for connecting an additional trailer (Correct answer)
It acts as an additional power unit when ascending steep grades

Correct answer: It converts the lead trailer's kingpin into a fifth-wheel coupling for connecting an additional trailer

A converter dolly has a fifth wheel on top that accepts the next trailer's kingpin, converting a standard trailer into a lead unit for a double or triple combination. It does not provide independent power or extra braking beyond what is already in the air system.

Question 32: What does the Air Compressor Governor control?

When the air is released from the tank
When water and oil are automatically expelled from the storage tanks
When the air compressor pumps air into the storage tanks (Correct answer)
When air pressure is cut to the front brakes

Correct answer: When the air compressor pumps air into the storage tanks

The air compressor governor is a critical component that regulates the air pressure in the air brake system. It controls the air compressor by telling it when to start pumping air into the storage tanks (cut-in pressure) and when to stop (cut-out pressure). This ensures that the system maintains optimal operating pressure without over-pressurizing the tanks.

Question 33: When you brake to a stop in a loaded tanker on a slippery road, what may happen after the vehicle stops?

The tank may lift off the ground
The brakes automatically hold longer
Nothing, the load stops with the truck
Liquid surge may push the vehicle forward (Correct answer)

Correct answer: Liquid surge may push the vehicle forward

Surge can continue after the stop and push the vehicle ahead, so keep the brakes applied.

Question 34: What is a common result of having too much weight on the steering axle?

Improved braking on wet roads
Reduced chance of a rollover
Increased drive-axle traction on snow
Hard steering and possible damage to the steering axle and tires (Correct answer)

Correct answer: Hard steering and possible damage to the steering axle and tires

Overloading the steering axle makes steering difficult and can damage the axle and tires.

Question 35: How does a high center of gravity from badly loaded cargo affect your vehicle?

It reduces stopping distance
It increases the risk of rollover (Correct answer)
It improves stability in curves
It has no effect on handling

Correct answer: It increases the risk of rollover

Heavy cargo loaded high raises the center of gravity, making the vehicle more likely to roll over on curves. Heavy items should be placed as low as possible.

Question 36: Where is compressed air stored?

Service and emergency air lines
Air compressor
Main reservoirs (Correct answer)
Pressure gauge

Correct answer: Main reservoirs

Compressed air, generated by the air compressor, is stored in large metal tanks called main reservoirs or air tanks. These tanks hold a reserve of compressed air, which is then supplied to the brake chambers and other air-operated accessories. Having these reservoirs ensures a constant supply of air pressure for braking, even if the compressor is not actively pumping.

Question 37: Why is it important to inspect the fuel tank cap during a pre-trip inspection?

Fuel cap inspection is performed by mechanics only at service intervals
To visually verify the fuel color
Only to estimate the fuel level without a gauge
To ensure it is secure and prevents fuel spills and flammable vapor release (Correct answer)

Correct answer: To ensure it is secure and prevents fuel spills and flammable vapor release

A secure fuel cap prevents fuel spills and the release of flammable vapors, reducing fire risk and preventing environmental contamination.

Question 38: If the trailer protection valve malfunctions, which of the following may occur?

Nothing will happen
The trailer air pressure will increase
A leak or trailer break away could drain all the air from the brake system (Correct answer)
The glad hands may uncouple

Correct answer: A leak or trailer break away could drain all the air from the brake system

The trailer protection valve is designed to prevent a complete loss of air pressure in the tractor's brake system if there's a major leak or breakaway in the trailer. If this valve malfunctions, a leak or a trailer breaking away could indeed drain all the air from the entire brake system, rendering both the tractor and trailer brakes inoperable. This is a critical safety feature.

Question 39: Which device helps reduce the risk of ice in the air brake systems during cold weather?

Safety valve
Air tank drain
Alcohol evaporator (Correct answer)
Air compressor governor

Correct answer: Alcohol evaporator

Alcohol evaporator. An alcohol evaporator puts alcohol into the air system to help reduce the risk of ice in cold weather. The governor controls when the air compressor will pump air into the air storage tanks. A safety valve protects the tank and system from too much pressure. The air tank drains allow you to drain oil and moisture from the air tanks.

Question 40: Why do bridge formulas limit axle weights based on axle spacing?

To shorten trailer lengths
To make placarding easier
To increase speed limits for heavy trucks
To keep heavy weight from concentrating too much on bridges by spreading it across axles (Correct answer)

Correct answer: To keep heavy weight from concentrating too much on bridges by spreading it across axles

Bridge formulas permit more weight when axles are farther apart, protecting bridges from concentrated loads.

Question 41: How should you brake when stopping normally?

Push the brake pedal down gradually, using a controlled amount of pressure (Correct answer)
Slam the pedal all the way down
Use only the engine brake
Pump the pedal quickly several times

Correct answer: Push the brake pedal down gradually, using a controlled amount of pressure

Smooth, gradual pressure brings the vehicle to a safe stop without skids or shifting the load.

Question 42: When is a driver NOT required to stop at a weigh station or agricultural inspection station that has a posted sign saying 'CMV Must Stop'?

When the driver holds a valid CMV inspection waiver issued by the state
Never — all drivers of commercial motor vehicles must stop when posted signs require it, unless directed otherwise by an officer (Correct answer)
When transporting perishable goods that are temperature-sensitive
When the vehicle is empty and weighs less than 10,001 lb

Correct answer: Never — all drivers of commercial motor vehicles must stop when posted signs require it, unless directed otherwise by an officer

All commercial motor vehicle drivers must stop at weigh stations and inspection checkpoints when required by posted signs. No federal exemption exists based on empty weight, cargo type, or inspection waiver.

Question 43: If you are checking the trailer emergency brakes what is the first thing you should ensure?

The trailer air brake system is charged. (Correct answer)
The trailer air brake system is completely empty.
You move the vehicle forward.
None of the listed answers.

Correct answer: The trailer air brake system is charged.

Before checking the trailer emergency brakes, it is crucial to ensure the trailer air brake system is fully charged. The emergency (spring) brakes on a trailer are held in the 'off' position by air pressure. If the system isn't charged, the emergency brakes will already be applied, preventing a proper test of their release and application functions.

Question 44: What is the purpose of a headerboard (front-end structure) on a flatbed trailer?

It provides extra lighting
It reduces wind resistance
It displays the carrier's name
It protects the cab from cargo shifting forward during hard braking (Correct answer)

Correct answer: It protects the cab from cargo shifting forward during hard braking

A headerboard or front-end structure stops cargo from sliding forward into the cab when you brake suddenly.

Question 45: If you press and release the brake pedal rapidly, what will happen?

Your vehicle will stop faster and straighter
You can cool your brakes rapidly
You can let the air out faster than the compressor can replace it (Correct answer)
You can safely control your speed around a curve

Correct answer: You can let the air out faster than the compressor can replace it

You can let the air out faster than the compressor can replace it. Releasing the brakes lets some compressed air out of the air brake system which results in the reduction of air pressure in the tank. Repeatedly pressing and releasing the brake pedal may reduce the air pressure faster than the compressor can replace it.

Question 46: What should you look for when inspecting wheel rims during a pre-trip inspection?

Only check for rim roundness visually
Rims only need inspection following a tire blowout
Only verify that the rims are the correct color
Cracks, damaged areas, and that all lug nuts are present and tightened (Correct answer)

Correct answer: Cracks, damaged areas, and that all lug nuts are present and tightened

Rims must be inspected for cracks, physical damage, and proper lug nut installation to prevent catastrophic wheel separation while driving.

Question 47: In which range should the spring brakes pop out (emergency brakes apply) on a vehicle with air brakes?

Between 55 and 70 psi
Between 20 and 45 psi (Correct answer)
Between 100 and 120 psi
Between 75 and 90 psi

Correct answer: Between 20 and 45 psi

Tractor protection and parking valves should pop out between 20 and 45 psi on typical systems.

Question 48: Which of the following devices should you use to prevent water and dirt from getting into the coupler and air lines when they are not in use?

Dead end or dummy couplers (Correct answer)
Tractor protection valve
Relay valves
Shut-off valves

Correct answer: Dead end or dummy couplers

Dead end or dummy couplers are essential devices used to protect the glad hands and air lines when they are not connected to a trailer. They prevent dirt, moisture, and other debris from entering the air brake system, which could cause damage or malfunction. Keeping the air lines clean is crucial for reliable brake performance.

Question 49: On the general skills test, you will be tested on what?

To see whether you know when your vehicle is safe to drive.
On your ability to control your vehicle.
All of the listed answers. (Correct answer)
Your ability to drive safely in a variety of traffic situations.

Correct answer: All of the listed answers.

The CDL general skills test is comprehensive, evaluating a driver's overall competency in several areas. It assesses your ability to control the vehicle safely, your knowledge of when the vehicle is safe to drive (which includes elements of the pre-trip inspection), and your performance in a variety of traffic situations during the on-road driving portion. This multi-faceted test ensures drivers possess the necessary skills for safe commercial operation.

Question 50: A CDL driver is convicted of a first DUI while operating a CMV carrying placarded hazardous materials. What is the minimum disqualification?

60 days
3 years (Correct answer)
1 year
Lifetime

Correct answer: 3 years

A first major offense while transporting placarded hazmat results in at least a 3-year disqualification.

Question 51: A lug nut area shows rust streaks radiating from the nuts. What does this most likely indicate?

Excess grease
Normal wear
Loose lug nuts (Correct answer)
Over-inflated tire

Correct answer: Loose lug nuts

Shiny rust trails or streaks around lug nuts typically mean the nuts are loose and moving.

Commercial Driver's License (CDL) General Knowledge

The CDL General Knowledge exam certifies an individual's understanding of the fundamental rules and regulations for operating commercial motor vehicles.

Questions

60 min

Time Limit

80%

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These practice questions were written with AI tools. They are not real exam questions. Exam facts are checked against the official sources listed below. Not reviewed by a subject-matter expert. Editorial policy

Sources & references

Exam facts on this page (fees, format, dates, passing scores) are checked against these official sources; the date is our last check. Editorial policy

tsa.gov — Fees, renewal · verified Oct 2026
ecfr.gov — Score validity, test delivery, retake policy, passing score · verified Oct 2026