Idaho General Knowledge CDL Practice Test

This is a free 20-question practice test for the General Knowledge portion of the Idaho 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 Idaho Transportation Department Division 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 Idaho.

Question 1 of 20

Maximum allowable steering-wheel play is approximately:

5 degrees
10 degrees
20 degrees
30 degrees

Correct. Steering wheel play should not exceed 10 degrees (roughly 2 inches on a 20-inch wheel). More than that, the vehicle is hard to steer.

Question 2 of 20

Which of the following is NOT part of the seven-step pre-trip inspection method?

Approach the vehicle and overview
Check the engine compartment
Test the AM/FM radio
Walk around inspection

Correct. The radio is not part of the safety inspection. The seven-step method covers approach, engine compartment, in-cab checks, lights, walk-around, signal lights, and brake checks.

Question 3 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.

Question 4 of 20

Stopping distance increases significantly when:

Brakes are wet
Tires are worn
You are heavily loaded
All of the above

Correct. Wet brakes, worn tires, heavy load, and slick pavement all extend stopping distance. Plan ahead and follow at greater intervals.

Question 5 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 6 of 20

When should you place reflective triangles on a divided highway after stopping due to a breakdown?

10, 50, and 100 feet behind the vehicle
10 feet to the rear, 100 feet to the rear, and 200 feet to the rear
10, 100, and 200 feet to the rear, on the traffic side
100, 200, and 500 feet to the rear

Correct. On a divided highway with traffic from one direction, place triangles 10, 100, and 200 feet behind the vehicle, on the shoulder or in the lane you stopped in.

Question 7 of 20

You are driving on a steep downgrade and your brakes have failed. The best escape is to:

Pump the brakes furiously
Use a runaway escape ramp
Try to bail out of the cab
Sound the horn and continue

Correct. If a runaway escape ramp is available, use it. Modern arrester beds use loose gravel or sand to slow the vehicle without injury to the driver.

Question 8 of 20

Which of the following is true about driving at night?

Headlights illuminate further than you can stop within
You should drive faster to keep up with traffic
You should drive at a speed that lets you stop within the distance illuminated by your headlights
You can rely on oncoming headlights to help you see

Correct. Drive at a speed where your stopping distance does not exceed the distance you can see — typically 250 feet on low beams, 350-500 feet on high beams.

Question 9 of 20

Federal regulations require a tie-down for every cargo, with a minimum of:

One tie-down for any cargo
One tie-down for items less than 5 feet long, two for items 5+ feet
At least one tie-down for each 10 feet of cargo, with minimums depending on length and weight
Tie-downs are not required for closed trailers

Correct. The general rule: at least one tie-down per 10 feet of article, plus a minimum based on length and weight (commonly two minimum for items over 5 feet or 1,100 lbs).

Question 10 of 20

When should you use four-way flashers?

Only when parked
When the vehicle is stopped or moving slowly enough to be a hazard to other traffic
Only at night
Whenever you want

Correct. Four-way emergency flashers warn other drivers when your vehicle is stopped or moving slowly relative to traffic.

Question 11 of 20

When should you use your high beams?

Whenever it is dark
When other drivers are within 500 feet ahead
When other drivers are not within 500 feet of you and you are not following another vehicle within 500 feet
In fog

Correct. Federal and state law requires you to dim high beams when within 500 feet of an oncoming vehicle, or when following within 500 feet of another vehicle.

Question 12 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 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

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 15 of 20

Doubling your speed roughly:

Doubles your stopping distance
Triples your stopping distance
Quadruples your stopping distance
Has no effect on stopping distance

Correct. Braking distance is proportional to the square of speed. Doubling speed roughly quadruples braking distance.

Question 16 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 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

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 19 of 20

On a tight curve in a rural mountain road:

Approach at posted speed
Slow down before entering the curve, take a wider line if you can do so safely
Speed up
Stay on the centerline

Correct. Mountain curves often have advisory speeds well below your safe load speed. Slow before entering and use the full lane safely.

Question 20 of 20

When you arrive at a customer to deliver:

Just open the trailer
Sign in, follow site safety rules (PPE, speed limits, designated routes)
Skip site rules
Park anywhere

Correct. Customer sites have their own safety rules — sign in, wear required PPE, follow speed limits and designated routes.

About the Idaho 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 Idaho Transportation Department Division 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 Idaho CDL practice tests.