Louisiana General Knowledge CDL Practice Test

This is a free 20-question practice test for the General Knowledge portion of the Louisiana Commercial Driver's License knowledge exam. Questions are pulled from a pool of 97 drawn from the AAMVA CDL Manual, which is the source document the Louisiana Office of Motor Vehicles uses to write its actual exam.

How it works: Click an answer. The correct choice highlights in green, and you'll see a short explanation. Aim for 85% or better before you sit for the real test in Louisiana.

Question 1 of 20

When the engine is running in the cab inspection, you should check:

Oil pressure, ammeter/voltmeter, coolant temperature, engine oil temperature, and air pressure
Only the speedometer
Only the air-pressure gauge
Only the fuel gauge

Correct. After starting, watch the gauges to be sure all systems are operating normally before you drive.

Question 2 of 20

When you exit a highway in a heavy commercial vehicle, you should:

Maintain highway speed onto the ramp
Slow down before reaching the ramp curve, since posted advisory speeds assume cars
Speed up to clear the ramp
Brake only at the bottom

Correct. Posted ramp speeds assume passenger cars. A loaded heavy vehicle, especially with high CG, can roll over at the posted speed. Slow before the curve.

Question 3 of 20

A driver convicted of driving a CMV with a BAC of .04 or higher faces:

No penalty
A warning
Disqualification of at least one year for the first offense
License renewal

Correct. A first conviction of driving a CMV with BAC ≥ .04 disqualifies the driver for at least one year (three years if hauling hazmat).

Question 4 of 20

The most important reason for doing a vehicle inspection is to:

Comply with the law
Save fuel
Find safety problems before they cause a crash
Document mileage

Correct. A pre-trip inspection is meant to find problems that could cause a crash or breakdown. Compliance is a side effect, not the purpose.

Question 5 of 20

What is "black ice"?

Ice that has been salted
A thin layer of ice clear enough that you can see the road through it
Ice on a black-painted road
Ice formed under the truck

Correct. Black ice is a thin, clear sheet of ice that looks like wet pavement. Suspect it whenever the temperature is at or below freezing and the road appears wet.

Question 6 of 20

How many red reflective triangles must you carry in your commercial vehicle for emergency warning?

One
Two
Three
Six

Correct. You must carry three red reflective triangles, six fusees, or three liquid-burning flares for emergency warning use.

Question 7 of 20

When a vehicle ahead of you brakes hard, you should:

Brake harder
Apply the brakes immediately, even if you don't need to
Look for a way to steer around the vehicle if necessary, while preparing to brake
Honk to warn the driver behind you

Correct. Plan your escape: identify a clear lane or shoulder. If you can steer to safety, you save reaction time. If not, brake firmly without locking the wheels.

Question 8 of 20

You are driving on a wet road. To test how slippery the road is, you can:

Brake hard at 50 mph
Accelerate hard and listen for tire spin
Gently apply the brakes at low speed
Look at other vehicles' tires

Correct. At low speed and in a safe place, you can gently test traction by lightly applying the brakes or by gently accelerating. Hard braking at high speed is dangerous.

Question 9 of 20

Hydroplaning is most likely to occur when:

Driving at low speed in light rain
Tires lose contact with the road and ride on water
Brakes are applied gently
Tires are over-inflated

Correct. Hydroplaning occurs when a film of water comes between the tires and the road, causing the tires to lose contact with the pavement. Higher speeds, worn tires, and standing water increase the risk.

Question 10 of 20

A driver should look down the road how far when driving at highway speeds?

One block
One-quarter mile (about 12-15 seconds ahead)
Just past the hood
To the horizon only

Correct. Look 12-15 seconds ahead — about a quarter mile at highway speeds. This gives time to identify and react to hazards.

Question 11 of 20

You should test your brakes before going down a hill by:

Driving down to test them
Pumping the pedal at the top
Lightly applying them as you start the descent to confirm they are working
Doing nothing

Correct. Just before the descent, gently apply the brakes at slow speed to confirm response. Combined with selecting a low gear in advance, this is the safe practice.

Question 12 of 20

You should never drive your vehicle if the brake-system warning device:

Comes on
Goes out
Flickers
Comes on briefly at startup

Correct. A continuously lit or sounding low-air warning means dangerous brake-system pressure loss. Stop safely and have the system serviced.

Question 13 of 20

The four-way flashers on a commercial vehicle should be used:

Anytime you are stopped or moving slowly enough that other drivers might not expect
Only when parked
Only at night
Only on the interstate

Correct. Use four-way flashers anytime your vehicle is stopped on or near the roadway, or moving slowly enough that approaching traffic might be surprised.

Question 14 of 20

When the brake pedal feels spongy on an air-brake vehicle:

It is normal
Stop and have the system checked — there may be air in the system or another issue
Drive faster
Pump the brakes harder

Correct. A spongy or unusual feel in air-brake pedals indicates a system issue. Have it inspected before continuing.

Question 15 of 20

Which of these is true about driving in fog?

Use high beams to see further
Use low beams; high beams reflect back and reduce visibility
Drive at the posted speed limit
Use the four-way flashers only when stopped

Correct. In fog, high beams reflect off water particles and impair vision. Use low beams. Many drivers also use four-way flashers when moving slowly to alert traffic.

Question 16 of 20

If your vehicle hydroplanes, what should you do?

Brake hard immediately
Steer sharply to recover
Release the accelerator and push in the clutch
Accelerate to push through

Correct. Release the accelerator and push in the clutch. Do not brake or steer hard until the tires regain contact.

Question 17 of 20

The blood-alcohol concentration (BAC) at or above which a CDL driver is considered to be driving under the influence in a commercial motor vehicle is:

Correct. The federal BAC limit for CDL drivers operating a commercial vehicle is .04 — half the .08 limit for non-commercial drivers in most states.

Question 18 of 20

Which type of fire extinguisher should you use on an electrical fire?

Class A
Class B
Class C
Class D

Correct. Class B:C dry-chemical extinguishers (often labeled "B:C" or "ABC") are appropriate for electrical fires. Never use water on an electrical fire.

Question 19 of 20

Cargo should be secured so that it does not shift:

More than 6 inches
Forward, backward, sideways, or upward
Only forward
Only sideways

Correct. Federal cargo-securement rules require that cargo not shift in any direction during normal driving conditions, including emergency braking.

Question 20 of 20

A fully loaded tractor-trailer traveling at 55 mph on dry pavement requires roughly what total stopping distance (perception + reaction + braking)?

100 feet
200 feet
300 feet (about the length of a football field)
600 feet

Correct. Total stopping distance for a heavy commercial vehicle at 55 mph on dry pavement is approximately 300 feet, or the length of a football field including end zones.

About the Louisiana General Knowledge exam

Most state DMVs administer 50 General Knowledge questions and require 80% (40 correct) to pass. Questions are pulled from a much larger pool, so two applicants taking the test on the same day will see different mixes. The questions on this site are drawn from the AAMVA CDL Manual chapters that every state's exam is built from.

The Louisiana Office of Motor Vehicles follows the federal CDL standards established by FMCSA. To earn the General Knowledge credential, you must answer at least 80% of the questions correctly. Many candidates score lower the first time because the test pulls from a large pool — refreshing this page will give you a different mix of questions, drawn from the same authoritative source.

Want more practice? Try the full General Knowledge question bank or browse all Louisiana CDL practice tests.