Kentucky General Knowledge CDL Practice Test

This is a free 20-question practice test for the General Knowledge portion of the Kentucky 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 Kentucky Department of Vehicle Regulation 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 Kentucky.

Question 1 of 20

Most drivers who fall asleep at the wheel:

Are aware they are tired and pull over
Do not realize they are about to fall asleep
Have been drinking
Have been on the road less than an hour

Correct. Most drivers who fall asleep do not realize how drowsy they are. The only fix is to stop and rest before fatigue reaches that point.

Question 2 of 20

What is the minimum tread depth required for the front (steering) tires of a commercial vehicle?

1/32 inch
2/32 inch
4/32 inch
6/32 inch

Correct. Steer-axle tires must have at least 4/32-inch tread depth in every major groove. Other tires require at least 2/32 inch.

Question 3 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 4 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 5 of 20

You are driving in a work zone. You should:

Drive faster to clear the zone
Slow down, increase following distance, watch for workers
Use the shoulder
Honk repeatedly

Correct. Work-zone fines double or more in most states. Slow down, give the vehicle ahead extra space, watch for workers and equipment, and follow signed speed reductions.

Question 6 of 20

Which of these is true about following distance for heavy vehicles?

It can be the same as a passenger car
It must be longer because heavy vehicles take longer to stop
It is irrelevant in city driving
It only matters at night

Correct. Greater weight = longer stopping distance. Use one second per 10 feet of vehicle length below 40 mph, plus an extra second above 40.

Question 7 of 20

A "convex mirror" on the side of a tractor:

Provides a wider view, but objects appear smaller and farther away than they really are
Magnifies objects
Has a flat reflection
Cannot be used in daylight

Correct. Convex (curved) mirrors widen the field of view but distort distance perception — objects look smaller and farther than they actually are.

Question 8 of 20

When you double your speed from 20 to 40 mph, the impact in a crash is:

Twice as great
Three times as great
Four times as great
The same

Correct. Crash energy is proportional to the square of speed. Doubling speed quadruples the energy of impact.

Question 9 of 20

Wet brakes can cause:

Reduced braking power, brakes pulling to one side, or wheel lockup
Better braking
No effect on the brakes
Improved fuel economy

Correct. After driving through deep water, brakes may be wet — they can lose effectiveness, pull to one side, or grab. Apply the brakes lightly while driving slowly to dry them.

Question 10 of 20

What is the only effective way to remove alcohol from the body?

Drinking coffee
Cold showers
Eating a heavy meal
Time

Correct. Only time eliminates alcohol from the body — at roughly one drink per hour. Coffee, food, and showers do not speed up the process.

Question 11 of 20

You are about to drive a vehicle that you have not driven before. What should you do?

Get in and drive — every commercial vehicle handles the same
Inspect the vehicle to make sure it is safe and the cargo is properly secured
Drive briefly without cargo to learn the controls
Skip the inspection if the previous driver inspected it

Correct. Federal regulations require the driver to be satisfied that the vehicle is in safe operating condition before driving. The previous driver's inspection does not relieve you of that responsibility.

Question 12 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 13 of 20

Which of these is a major cause of crashes in heavy vehicles?

Driver fatigue
Heavy traffic
Following too closely
All of the above

Correct. Fatigue, heavy traffic, and following too closely are all leading factors in commercial vehicle crashes.

Question 14 of 20

When driving down a long, steep downgrade, you should:

Hold the brakes lightly the whole way down
Select the proper gear before starting down and use intermittent firm brake applications
Coast in neutral
Use only the engine brake

Correct. Select a low gear before starting down. Use the brakes in firm, intermittent applications: brake until 5 mph below safe speed, release until safe speed is regained, repeat. Continuous brake application overheats the brakes.

Question 15 of 20

A driver who has been disqualified is:

Allowed to drive a commercial vehicle
Not allowed to drive a commercial vehicle
Allowed to drive only with another driver in the cab
Allowed to drive only on private property

Correct. A disqualified driver may not operate a commercial motor vehicle on public roads, regardless of supervision.

Question 16 of 20

When approaching a railroad crossing, drivers of buses, school buses, and placarded hazmat vehicles must:

Speed up to clear quickly
Stop between 15 and 50 feet from the nearest rail and listen
Cross only if a train is in sight
Sound the horn

Correct. Buses, school buses, and placarded hazmat vehicles must stop at every crossing, 15 to 50 feet from the nearest rail. Look and listen, then proceed when safe.

Question 17 of 20

What does it mean when a driver is "hydroplaning"?

The truck is overheating
The tires lose contact with the road and ride on a film of water
The brakes have failed
The driver is dehydrated

Correct. Hydroplaning means tires have lost contact with the pavement and are riding on standing water. Steering and braking become ineffective.

Question 18 of 20

Which of the following is true about the front-end shock absorbers?

They have nothing to do with handling
Worn shock absorbers can cause poor handling and uneven tire wear
They are part of the brake system
They affect only ride comfort, never safety

Correct. Shock absorbers control suspension oscillation. Worn shocks contribute to poor handling, uneven tire wear, and reduced control on rough roads.

Question 19 of 20

You should signal:

Only when other vehicles are visible
Continuously while driving
Well before any turn or lane change, and signal long enough to communicate
Only when changing lanes left

Correct. Signal early, signal long enough that other drivers see and process the signal, and cancel after the maneuver.

Question 20 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.

About the Kentucky 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 Kentucky Department of Vehicle Regulation 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 Kentucky CDL practice tests.