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

Question 1: What is the proper technique to use when braking on downgrades?

Use controlled braking
Apply the brakes just hard enough to slowdown about 5 mph below your safe speed (Correct answer)
Use stab braking
Repeatedly pump the brakes to slow the vehicle down

Correct answer: Apply the brakes just hard enough to slowdown about 5 mph below your safe speed

Apply the brakes just hard enough to slowdown about 5 mph below your safe speed. When going down a long/steep downgrade you should use engine braking to slow your vehicle down. After your vehicle is in the proper gear, you can apply the brakes just hard enough to feel a definite slowdown (usually about three seconds). When your speed is about 5 MPH below your safe speed, you can release the brakes.

Question 2: Why should you never smoke near a vehicle carrying flammable hazardous materials?

Ignition sources can cause fire or explosion (Correct answer)
It violates parking rules only
Smoke can stain the placards
It is bad for fuel economy

Correct answer: Ignition sources can cause fire or explosion

Flammable materials can ignite from sparks, flames, or burning cigarettes, causing fire or explosion.

Question 3: CONVEX MIRRORS WILL:

None of the answers are correct
Make objects appear larger than they actually are
Make objects appear closer than they actually are
Show a wider view than flat mirrors (Correct answer)

Correct answer: Show a wider view than flat mirrors

Convex mirrors are designed with a curved surface that allows them to show a wider field of view compared to flat mirrors. This wider view is beneficial for commercial drivers to see blind spots and more of the surrounding traffic. However, a drawback is that objects viewed in convex mirrors appear smaller and farther away than they actually are, requiring drivers to adjust their perception.

Question 4: What is the name of the device that controls when the air compressor will pump air into the air storage tanks?

Safety valve
Evaporator
Air tank drains
Governor (Correct answer)

Correct answer: Governor

Governor. The governor controls when the air compressor will pump air into the air storage tanks. An alcohol evaporator puts alcohol into the air system to help reduce the risk of ice in cold weather. 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 5: What is another term for a brake pedal?

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

Correct answer: Treadle valve

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

Question 6: Which of the following parts should you check for cracks?

Brake hoses.
Brake chambers.
All of the listed answers. (Correct answer)
Brake drums.

Correct answer: All of the listed answers.

During a pre-trip inspection, it is essential to thoroughly check all brake components for cracks, which can indicate structural weakness and potential failure. This includes the brake chambers, brake drums, and brake hoses. Cracks in any of these parts can compromise braking effectiveness and lead to dangerous situations on the road.

Question 7: When must a school bus driver use red flashing lights and the stop arm?

Only on highways
Whenever driving at night
When stopped to load or unload students (Correct answer)
Only when the bus is empty

Correct answer: When stopped to load or unload students

Red flashing lights and the stop arm are used when the bus is stopped to load or unload passengers.

Question 8: What is the purpose of a front-brake limiting valve?

Expel water and oil.
Reduce the air to the front brakes.
Increase your vehicle's speed.
Reduce the air to the front brakes and reduce the stopping power of the vehicle. (Correct answer)
Reduce the stopping power of the vehicle only.

Correct answer: Reduce the air to the front brakes and reduce the stopping power of the vehicle.

The front-brake limiting valve is designed to reduce the air pressure supplied to the front brakes, thereby reducing their stopping power. This is particularly important on older vehicles or in certain conditions, as it helps prevent the front wheels from locking up before the rear wheels. Preventing front wheel lock-up helps maintain steering control during braking, especially on slippery surfaces.

Question 9: Which tire condition requires taking a commercial vehicle out of service immediately?

A missing valve stem cap on one tire
Minor surface scuffs from curb contact
Tires below minimum tread depth or showing visible cord or sidewall bulges (Correct answer)
Slight road dust on the tire sidewalls

Correct answer: Tires below minimum tread depth or showing visible cord or sidewall bulges

Tires with insufficient tread depth, exposed cord, or structural damage such as bulges present serious blowout risk and require the vehicle to be taken out of service.

Question 10: Cargo such as dry bulk or hanging meat

Have high centers of gravity and are unstable loads (Correct answer)
Require special transit permits
Require no special driving attention
Have low centers of gravity and can lean on curves

Correct answer: Have high centers of gravity and are unstable loads

Cargo such as dry bulk (like grain) or hanging meat can shift easily and often have a high center of gravity. These characteristics make them unstable loads, significantly increasing the risk of rollovers, especially when taking curves or making sudden maneuvers.

Question 11: When backing a combination vehicle, why is it always better to back to the driver's side?

It is required by federal law
It keeps the trailer wheels off the shoulder
It reduces fuel consumption while reversing
You can watch the rear of your trailer through the side window (Correct answer)

Correct answer: You can watch the rear of your trailer through the side window

Backing to the driver's side lets you see the trailer's position by looking out the side window, while sight-side backing avoids blind-side guesswork.

Question 12: Which of the following hazardous material loads is acceptable to transport on a bus?

10 pounds of liquid Class 6 poison
10 pounds of Class 1 explosives, other than small arms ammunition
100 pounds of solid Class 6 poison (Correct answer)
Radioactive materials (less than 2 ounces) in the space occupied by people

Correct answer: 100 pounds of solid Class 6 poison

Federal regulations (49 CFR) strictly limit the types and quantities of hazardous materials that can be transported on a bus carrying passengers. While many hazardous materials are prohibited, certain small quantities of specific classes, such as 100 pounds of solid Class 6 poison, are permitted under specific conditions. Other options like liquid poisons, explosives, or radioactive materials in passenger compartments are generally forbidden due to higher risks.

Question 13: What must a CDL driver do if safety-affecting defects are found during a pre-trip inspection?

Report them only at the end of the trip
Have defects repaired before operating the vehicle (Correct answer)
Note them in the trip log and continue driving
Defects only need to be reported to a supervisor monthly

Correct answer: Have defects repaired before operating the vehicle

Safety-affecting defects must be repaired before operating the vehicle; drivers are legally responsible for ensuring the vehicle is in safe operating condition.

Question 14: As part of your pre-trip vehicle inspect test, you should look under the vehicle for ______.

Grease
All of the listed answers. (Correct answer)
Fresh oil.
Fuel leaks.
Coolant.

Correct answer: All of the listed answers.

During a pre-trip vehicle inspection, it is essential to thoroughly check under the vehicle for any signs of leaks. Fresh oil, coolant, fuel, and grease leaks can indicate serious mechanical problems that could lead to breakdowns or safety hazards. Identifying these leaks before starting a trip allows for timely repairs and prevents potential issues on the road.

Question 15: When uncoupling a semi-trailer, you should lower the landing gear BEFORE disconnecting the air lines. Why?

To support the trailer's front end and prevent it from dropping and damaging the air lines and electrical cord (Correct answer)
Because the service line must stay connected until the landing gear locks into position
So the emergency air line stays pressurized to keep the trailer brakes released while you crank
The air pressure is needed to power the electric–over–air landing gear motor

Correct answer: To support the trailer's front end and prevent it from dropping and damaging the air lines and electrical cord

If you disconnect the air and electrical lines before the landing gear is down and bearing weight, the front of the trailer can drop suddenly, tearing apart the lines and potentially injuring anyone nearby or damaging equipment.

Question 16: You must have a CDL to operate ________.

30
180 (Correct answer)
60
90

Correct answer: 180

The correct answer '180' days refers to the suspension period for certain serious CDL violations, such as a second violation of an out-of-service order within a 10-year period. It can also apply to a first out-of-service violation if transporting hazardous materials or operating a vehicle designed for 16 or more passengers. This penalty enforces strict adherence to safety regulations and ensures drivers comply with mandatory rest periods or vehicle repair requirements.

Question 17: What should you look for when inspecting wheel rims during a pre-trip inspection?

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)
Only check for rim roundness visually

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 18: ________ is the first and most important thing you should do during an emergency.

Leading students to a safe area.
Recognizing the type of hazard. (Correct answer)
Calling the parents of the children.
Evacuating the bus.

Correct answer: Recognizing the type of hazard.

In any emergency situation, the first and most crucial step is to quickly and accurately recognize the type of hazard present. This initial assessment dictates all subsequent actions, such as whether to evacuate the bus, how to protect students, or what emergency services to contact. A correct hazard assessment ensures the most appropriate and effective response to mitigate danger.

Question 19: When should a bus driver check mirrors while operating in traffic?

Only when changing lanes or merging, to avoid distraction on straight sections
Every 15–20 seconds to maintain attention on the road ahead
Only at intersections and bus stops where pedestrian activity is highest
Every 5–8 seconds as part of a systematic scanning pattern, more frequently in congested areas (Correct answer)

Correct answer: Every 5–8 seconds as part of a systematic scanning pattern, more frequently in congested areas

Systematic mirror scanning every 5–8 seconds — and more often in heavy traffic — keeps the driver aware of vehicles in blind spots, following traffic, and pedestrians near the bus.

Question 20: If you are transporting cargo, you should inspect the cargo and securing devices

Before the trip, within 50 miles after beginning the trip, and at least every 150 miles or 3 hours (Correct answer)
During every driving brake on the trip
Before the trip
Within the first 50 miles of driving

Correct answer: Before the trip, within 50 miles after beginning the trip, and at least every 150 miles or 3 hours

Regular inspection of cargo and securing devices is critical for safety. Federal regulations require inspections before the trip, again within the first 50 miles of driving (as cargo can settle), and then at least every 150 miles or 3 hours, whichever comes first, to ensure cargo remains secure throughout the journey.

Question 21: Buses built before _____ have been voluntarily equipped with ABS.

2005
2010
2001
1998 (Correct answer)

Correct answer: 1998

While Antilock Braking Systems (ABS) became mandatory for most new commercial vehicles, including buses, after a certain date, some manufacturers voluntarily equipped their vehicles with ABS prior to this requirement. Specifically, buses built before March 1, 1998, may have been voluntarily equipped with ABS, offering enhanced safety features before they were federally mandated.

Question 22: When you are backing up a straight truck, you turn the top of the steering wheel ______.

Always to the right.
In the opposite direction of where you want to go.
In the direction you want to go. (Correct answer)
Always to the left

Correct answer: In the direction you want to go.

When backing a straight truck, the steering works the same way as when driving forward. To move the rear of the truck to the left, you turn the steering wheel to the left, and to move it to the right, you turn the wheel to the right. This direct correlation makes backing a straight truck simpler than backing a truck with a trailer.

Question 23: Which of the following statements is true regarding front wheel braking?

You should put a front brake limiting valve (if equipped) on the slippery position in adverse conditions
Front wheel braking is good under all conditions (Correct answer)
Front wheel braking is ineffective in slippery conditions
Front wheel braking will cause skids on ice

Correct answer: Front wheel braking is good under all conditions

Modern commercial vehicles are designed with front wheel brakes that are effective and necessary for optimal stopping power under all conditions. While older systems might have had front brake limiting valves for slippery conditions, current regulations and designs ensure front brakes contribute significantly to overall braking performance without causing skids when properly maintained and operated.

Question 24: This rectangular sign with red lettering and symbol, indicates what?

You may not park on the side of the road in this direction. (Correct answer)
You may only park here for one hour.
No parking here Monday - Friday.
If you have the correct permit, parking is acceptable.

Correct answer: You may not park on the side of the road in this direction.

This sign, often a 'NO PARKING' sign with an arrow, indicates that parking is prohibited from the sign's location in the direction the arrow points. It is a regulatory sign designed to keep certain areas clear for traffic flow, emergency access, or other safety reasons. Drivers must find an alternative parking spot.

Question 25: A 'kingpin' is the part of a combination vehicle that:

Connects the brake chambers
Locks into the fifth wheel of the tractor (Correct answer)
Secures the mud flaps
Holds the landing gear in place

Correct answer: Locks into the fifth wheel of the tractor

The kingpin is the steel pin on the trailer that locks into the fifth-wheel jaws of the tractor.

Question 26: What should the air pressure loss be in a single vehicle with a fully charged air system?

Less than 2 psi per minute (Correct answer)
Less than 5 psi per minute
Less than 3 psi per minute
Less than 4 psi per minute

Correct answer: Less than 2 psi per minute

During a static air brake test, a single vehicle with a fully charged air system should not lose more than 2 psi in one minute after the initial pressure drop from applying the brakes. This low rate of pressure loss indicates that the air brake system is relatively free of leaks. Exceeding this limit suggests a problem that needs to be addressed for safe vehicle operation.

Question 27: If your vehicle does not have automatic air tank drains, how often should you drain the tanks?

Every 1,000 miles of travel
Twice a week
At the end of each working day (Correct answer)
Once a week

Correct answer: At the end of each working day

At the end of each working day. Draining the air tanks removes oil and moisture. If you do not drain each working day, you risk brake failure.

Question 28: On newer vehicles what color is the parking brake knob?

Red.
Green.
Blue.
Yellow. (Correct answer)

Correct answer: Yellow.

In newer commercial vehicles, the parking brake knob is typically yellow. This standardized color helps drivers quickly identify the parking brake control, enhancing safety and operational efficiency. It serves as a key visual indicator for this critical safety component.

Question 29: Under FMCSA regulations, how far must flares, fusees, or other attended lighted warning devices be kept from a vehicle carrying Class 3 flammable liquids?

Flares may be used only if the flammable liquids are sealed in an inner container
At least 10 feet from the vehicle on each side
At least 50 feet from the vehicle at the front and rear
Flares and fusees may NOT be used; only reflective triangles or other non-flame-producing devices are permitted (Correct answer)

Correct answer: Flares and fusees may NOT be used; only reflective triangles or other non-flame-producing devices are permitted

When a vehicle is transporting flammable liquids, gases, or explosives, flame-producing warning devices (flares, fusees) are prohibited entirely. Only reflective triangles, electric lights, or other non-incendiary devices may be used as emergency warning signals.

Question 30: What is required when fueling a vehicle carrying hazardous materials?

The driver must leave the area entirely
Someone must control the fuel nozzle and no smoking is allowed (Correct answer)
Placards must be removed first
The engine must be running

Correct answer: Someone must control the fuel nozzle and no smoking is allowed

A person must always control the fuel flow at the nozzle, and smoking is prohibited during fueling.

Question 31: The trailer hand valve (trolley valve) should be used:

For all normal stops
Only to test the trailer brakes, never for parking (Correct answer)
As a parking brake
To unlock the fifth wheel

Correct answer: Only to test the trailer brakes, never for parking

The hand valve should only be used to test trailer brakes; using it to hold a parked vehicle is dangerous and it can apply trailer brakes alone and cause a skid in driving.

Question 32: Which of the following devices can be used as the low air pressure warning signal?

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

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 33: How should service brakes be tested during a pre-trip inspection?

Apply brakes at low speed and check that the vehicle stops promptly and evenly without pulling (Correct answer)
Only depress the brake pedal while the vehicle is stationary
Service brakes are only tested by certified mechanics
Test brakes only at highway speed to simulate real conditions

Correct answer: Apply brakes at low speed and check that the vehicle stops promptly and evenly without pulling

Service brakes should be tested by applying them firmly at low speed and verifying that the vehicle stops promptly and evenly without pulling to one side.

Question 34: Which of the following is a necessary step to test your service brakes?

Move the vehicle forward slowly.
Wait for normal air pressure.
Release the parking brake.
All of the listed answers. (Correct answer)

Correct answer: All of the listed answers.

To properly test your service brakes, you must first ensure the air pressure is at normal operating levels. Then, release the parking brake and move the vehicle forward slowly, typically around 5 mph. Applying the service brake firmly at this low speed allows you to check if the vehicle stops smoothly and if the brakes pull to one side, confirming proper function.

Question 35: When is a CDL driver required to perform a pre-trip inspection?

Once a week before long trips
Before each trip (Correct answer)
Every 500 miles during a trip
Only after repairs have been made

Correct answer: Before each trip

Federal regulations require CDL drivers to inspect their vehicle before each trip to ensure it is safe to operate.

Question 36: HOW CAN YOU TEST THE TRAILER EMERGENCY BRAKES?

Place the tractor emergency valve in the emergency position, try to nudge the vehicle forward (Correct answer)
With full air tanks and the engine off, press on the brake pedal several times
Open shut-off valves on both air lines at the rear of the last trailer
Release the parking brake and nudge the vehicle forward

Correct answer: Place the tractor emergency valve in the emergency position, try to nudge the vehicle forward

To test the trailer emergency brakes, first ensure your air tanks are fully charged. Then, pull out the trailer air supply (emergency) valve, which should cause the trailer's emergency brakes to apply. With the trailer brakes engaged, gently try to pull the vehicle forward with the tractor. If the trailer brakes are working correctly, they will hold the trailer firmly in place, preventing it from moving.

Question 37: WHAT MIGHT HAPPEN IF THE TRAILER IS TOO HIGH WHEN YOU TRY TO COUPLE?

The trailer may start rolling
The trailer may not couple correctly (Correct answer)
You will not be able to connect the electrical cord
You will not be able to connect the air lines

Correct answer: The trailer may not couple correctly

If the trailer is too high during coupling, the kingpin may not properly enter the fifth wheel's locking jaws, or the jaws may not fully close around the kingpin's shank. This can result in a 'high hook,' where the trailer is not securely attached to the tractor. A high hook is extremely dangerous as the trailer could separate from the tractor during transit, leading to a catastrophic accident.

Question 38: Trailer brakes that come on automatically when the air supply is lost are called:

Trolley brakes
Parking pawls
Emergency (spring) brakes (Correct answer)
Service brakes

Correct answer: Emergency (spring) brakes

Spring brakes apply automatically when air pressure drops, providing an emergency braking function.

Question 39: What does this yellow, diamond shaped sign with red/black/white symbols warn you about?

3-point turn ahead.
Bus stop.
An upcoming yield sign. (Correct answer)
Runaway vehicle ramp.

Correct answer: An upcoming yield sign.

This yellow diamond-shaped sign, often depicting a triangular yield sign symbol, serves as an advance warning that a yield sign is ahead. It gives drivers time to prepare to slow down and be ready to yield the right-of-way to other traffic at the upcoming intersection or merge point. This helps prevent sudden stops and collisions.

Question 40: How fast should the air pressure build in a dual air system?

From 85 to 100 psi in 45 seconds (Correct answer)
From 50 to 90 psi in 3 minutes
From 70 to 125 psi in 60 seconds
From 100 to 150 psi in 45 seconds

Correct answer: From 85 to 100 psi in 45 seconds

From 85 to 100 psi in 45 seconds. In a single air system, the pressure should build from 50 to 90 psi in 3 minutes.

Question 41: Why is checking wiper blades included in a pre-trip inspection?

Only the washer fluid level needs checking, not the blades
To ensure they produce the correct squeak sound
To verify they clear the windshield effectively and are not damaged or worn (Correct answer)
Wipers only require inspection before winter driving season

Correct answer: To verify they clear the windshield effectively and are not damaged or worn

Wiper blades must be in good condition and operate effectively to maintain adequate visibility in rain or adverse weather, which is critical for safe driving.

Question 42: When checking the horn during a pre-trip inspection, what must be verified?

That it matches the vehicle manufacturer's specifications exactly
Only air horns need to be checked on commercial vehicles
That it produces a pleasant sound
That it works and is loud enough to serve as an effective warning device (Correct answer)

Correct answer: That it works and is loud enough to serve as an effective warning device

The horn must work and produce sufficient volume to warn other road users, as it is a required safety device under federal regulations.

Question 43: While driving, the driver of hazardous materials should wear a seat belt and the shipping papers should be ________.

In back of the car.
Safely hidden.
On the driver seat all times.
Within reach at all times. (Correct answer)

Correct answer: Within reach at all times.

For safety and regulatory compliance, a driver transporting hazardous materials must always wear a seat belt. Additionally, the shipping papers containing vital information about the hazardous cargo must be kept within immediate reach at all times while driving. This ensures that in an emergency, the driver or first responders can quickly access critical details about the materials being transported.

Question 44: What will happen if your air compressor stops?

You will have an immediate loss of your brakes
Your brakes will not be affected
Your brakes will lock up
You'll still have air pressure left in the air tanks to stop (Correct answer)

Correct answer: You'll still have air pressure left in the air tanks to stop

You'll still have air pressure left in the air tanks to stop. If your compressor stops working, you will still have air pressure left in your tanks, but the air compressor will not be able to replace air lost by using your brakes.

Question 45: A safe place to evacuate students will generally be at least 100 ft. off the road except when ________.

The bus is on fire.
You are stuck on the railroad tracks.
There is never an instance when a safe area is 100 ft. away from the road.
There is a risk of spilled hazardous materials. (Correct answer)

Correct answer: There is a risk of spilled hazardous materials.

While 100 feet off the road is a general guideline for evacuating students to a safe area, this distance is insufficient if hazardous materials are involved. In the event of a hazardous material spill, the safe evacuation distance must be significantly greater, often hundreds or thousands of feet, depending on the material and wind conditions. The primary goal is to move students far enough away to avoid exposure to dangerous fumes or substances.

Question 46: When you are securing cargo, blocking and bracing are used to ________.

Prevent cargo movement. (Correct answer)
Protect the area around an accident.
Prevent slow mobility.
Stop tailgaters.

Correct answer: Prevent cargo movement.

Blocking and bracing are essential cargo securement techniques. Blocking involves placing objects to fill gaps and prevent cargo from sliding, while bracing uses supports to prevent tilting or shifting. Both methods work together to ensure cargo remains stable and does not move during transit, which is crucial for safety and preventing damage.

Question 47: What does audible air leaking from the brake system during a pre-trip inspection indicate?

There is a leak in the air brake system that must be repaired before the vehicle is operated (Correct answer)
This is normal and indicates the compressor is running
Air leaks are only a concern at speeds above 60 mph
The compressor is building extra reserve pressure, which is beneficial

Correct answer: There is a leak in the air brake system that must be repaired before the vehicle is operated

Air leaks reduce brake system pressure, compromising stopping ability, and must be repaired before the vehicle is operated to ensure safe braking.

Question 48: A general rule for tying down cargo: you need one tiedown for each _____ ft. of cargo.

20 ft.
30 ft.
15 ft.
10 ft. (Correct answer)

Correct answer: 10 ft.

According to federal regulations for cargo securement, a general rule is that you need one tiedown for each 10 feet of cargo length. This ensures that the cargo is adequately secured along its entire length, preventing shifting during transit. Proper tiedown placement is crucial for maintaining vehicle stability and preventing accidents.

Question 49: Which of the following would NOT be part of a standard vehicle inspection?

Tire problems
Seating defects (Correct answer)
Steering system defects
Bad brake drums or shoes

Correct answer: Seating defects

A standard commercial vehicle inspection, such as a pre-trip inspection, focuses on critical safety components that could impact the vehicle's operation or lead to an accident. This includes checking tires, brakes, steering, lights, and cargo securement. While comfortable and functional seating is desirable, defects in the seating itself are generally not considered safety-critical items that would be part of a standard regulatory inspection or cause an out-of-service condition.

Question 50: You could experience steering problems because of friction between the tractor and trailer if you do not lubricate which of the following?

Dead end couplers
Fifth wheel plate (Correct answer)
Relay valves
Glad hands

Correct answer: Fifth wheel plate

The fifth wheel plate is the large, flat surface on the tractor that supports the trailer's kingpin. Proper lubrication of this plate is crucial to reduce friction between the tractor and trailer during turns and maneuvers. Without adequate lubrication, excessive friction can lead to steering problems, binding, and potential damage to the coupling system.

Question 51: What should you do before driving a vehicle with a dual air system?

Make sure that primary system builds up to 125 psi and secondary system builds up to 100 psi
Make sure that primary system builds up to 100 psi and secondary system builds up to 85 psi
Make sure both primary and secondary system build up to 85 psi
Make sure that both primary and secondary system build up to 100 psi (Correct answer)

Correct answer: Make sure that both primary and secondary system build up to 100 psi

Make sure that both primary and secondary system build up to 100 psi. Before driving a vehicle with a dual air system, you should allow enough time for the air compressor to build up a minimum of 100 psi on both systems. You should verify this by watching both air pressure gauges.

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.

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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

ecfr.gov — Passing score, test delivery, retake policy, eligibility, score validity · verified Oct 2026
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