IL · GK Endorsement

Illinois General Knowledge CDL Practice Test

Below are 25 exam-style questions for the Illinois General Knowledge CDL knowledge test, modeled on the FMCSA-aligned content used by the Illinois Secretary of State. Try to answer each question on your own before reading the answer key directly under it. The questions and answer choices are shuffled deterministically per state and endorsement, so the order will stay the same on repeat visits — that lets you genuinely measure your improvement.

Heads up: this is a study tool, not a graded exam. Cover the answer with your hand or a sheet of paper for an honest practice run, then re-read the explanations for any questions you missed. Aim for 22 out of 25 or better, three times in a row, before scheduling the real exam.

Question 1 of 25

A CDL is required to operate a single vehicle with a GVWR of:

A 20,000 lbs or more
B 40,000 lbs or more
C 26,001 lbs or more
D 10,001 lbs or more

Correct answer: C

Single vehicles at or above 26,001 lbs GVWR (Class B) require a CDL. Class A applies to combinations at or above 26,001 lbs GCWR with a trailer over 10,000 lbs.

Question 2 of 25

When driving at night, you should adjust speed so that you can stop within:

A Half the range of your low-beam headlights
B The full range of high-beam headlights when in use
C The range of your low-beam headlights
D Whatever speed feels safe

Correct answer: C

Always be able to stop within the distance you can see. At night with low beams, that's typically about 250 feet.

Question 3 of 25

Stab braking is used:

A On wet roads only
B On vehicles without ABS, to keep them straight in an emergency
C To save fuel
D On vehicles with ABS

Correct answer: B

Stab braking — full application then release as soon as wheels lock, then re-apply — is for non-ABS vehicles. With ABS, do not pump.

Question 4 of 25

The minimum tread depth for steer-axle tires is:

A 2/32 inch
B 4/32 inch
C 6/32 inch
D 1/32 inch

Correct answer: B

Steer tires must have at least 4/32 inch in every major groove. Other tires require at least 2/32 inch.

Question 5 of 25

On a long downgrade, why is it dangerous to use the brakes too much?

A Brake fade can leave you with reduced or no braking power
B It wastes brake pads
C It cools the brakes too much
D It triggers the ABS warning light

Correct answer: A

Heat from continuous braking causes the friction surfaces to lose their grip. Use a low gear and brief, moderate brake applications.

Question 6 of 25

Which is true about driving in mountains?

A Brakes alone are not designed to hold a heavy vehicle on a long downgrade
B All of the above
C Engine braking helps keep speed under control
D Heavy vehicles can slow down sharply on grades

Correct answer: B

Mountain driving combines all three. Use of low gears, engine braking, and short, moderate service-brake applications is the safe combination.

Question 7 of 25

Hours-of-service records are required to be kept by:

A No one
B The driver, in the form of a logbook or electronic logging device
C The carrier only
D The dispatcher only

Correct answer: B

Drivers are responsible for accurate hours-of-service records, kept either on paper logs or, for most carriers, on an ELD.

Question 8 of 25

Which is true about brake lining wear and adjustment?

A Brake adjustment is the dispatcher's responsibility
B Slack adjusters need periodic checking; pushrod travel beyond limits is out-of-service
C Brakes self-adjust forever
D Drum brakes never need adjustment

Correct answer: B

Slack adjusters can fail, and pushrod travel must be within limits. Drivers check; adjustment itself is a maintenance task for qualified personnel.

Question 9 of 25

When should you do an en-route inspection?

A Only when the load is hazardous
B Only if a warning light comes on
C At the end of the trip
D Within the first 25 miles, then about every 150 miles or every 3 hours

Correct answer: D

The FMCSA model manual recommends a check within the first 25 miles to catch loose cargo or under-inflated tires that have warmed up, then about every 150 miles or 3 hours, and any time you stop.

Question 10 of 25

How does ABS help in an emergency stop?

A It prevents wheel lockup so the driver can keep steering
B It increases brake pressure automatically
C It applies the parking brake
D It always stops the vehicle in a shorter distance

Correct answer: A

ABS keeps the wheels rolling so steering control is preserved. It is not a shorter-distance device.

Question 11 of 25

A driver may keep moving when:

A A vehicle is in safe operating condition
B Required emergency equipment is missing
C A trailer brake light is out
D A passenger door is open

Correct answer: A

Federal rules forbid driving any CMV that is not in safe operating condition. Continue only after the defect is fixed.

Question 12 of 25

The two main reasons why a driver's feet are kept off the brakes when not actively braking are:

A So the brake lights don't mislead following drivers and so the brakes don't overheat
B To save fuel and improve mileage
C To rest the right leg
D To save brake pads and reduce drag

Correct answer: A

Riding the brake lights confuses drivers behind you and gradually heats the friction surfaces, both of which are safety problems.

Question 13 of 25

A controlled braking technique means:

A Coasting in neutral
B Locking the wheels
C Pumping the brakes hard and fast
D Applying the brakes as hard as possible without locking the wheels

Correct answer: D

Controlled braking applies brakes hard but stops short of wheel lock-up. With ABS, you can simply press and hold full pressure.

Question 14 of 25

When you double your speed, your stopping distance approximately:

A Triples
B Quadruples
C Doubles
D Stays the same

Correct answer: B

Braking distance increases roughly with the square of speed; doubling speed quadruples the braking distance. Reaction distance only doubles, but the total grows quickly.

Question 15 of 25

Which is true about driving in rain?

A Roads are most slippery just after rain begins, when water mixes with road oil
B High beams improve visibility in heavy rain
C It is safe to drive at the posted speed limit
D Tire chains are required by federal law

Correct answer: A

The first few minutes of rain mix with oil and grime on the road and create the slipperiest conditions. Slow down and increase following distance.

Question 16 of 25

Which of the following is true about cargo securement?

A You must inspect cargo and securement before driving and within the first 50 miles
B Cargo is the shipper's responsibility, not yours
C Federal rules do not apply to cargo securement
D Tying a load down once at the start is enough

Correct answer: A

49 CFR Part 393 makes the driver responsible for inspecting cargo and its securement before driving and again within the first 50 miles, then every 150 miles or 3 hours.

Question 17 of 25

What does GVWR stand for?

A General Vehicle Weight Reading
B Gross Vehicle Weight Rating
C Gross Vehicle Width Rating
D Government Vehicle Weight Regulation

Correct answer: B

GVWR is the maximum weight the manufacturer says a single vehicle can safely weigh, including itself plus its load.

Question 18 of 25

Which of the following is a sign of fatigue?

A Trouble remembering the last few miles
B Frequent yawning
C All of the above
D Drifting in your lane

Correct answer: C

All three are classic fatigue indicators in the FMCSA model. Cold air, music, and caffeine are not effective fixes — only sleep is.

Question 19 of 25

A vehicle's "no-zone" is:

A A federal speed restriction
B The fuel tank area
C The area in front of the steer axle
D The area immediately next to it where other drivers are hidden in your blind spots

Correct answer: D

No-zones are the four blind-spot areas (front, rear, and both sides) where smaller vehicles are difficult or impossible to see in your mirrors.

Question 20 of 25

Which is true about driving in fog?

A Drive faster to get out of the fog quickly
B Use high-beam headlights for maximum visibility
C Use low-beam headlights and slow down
D Use the four-ways while in motion at highway speed

Correct answer: C

High beams reflect off fog and reduce visibility. Slow down and use low beams or fog lamps if equipped.

Question 21 of 25

A driver should test the parking brake by:

A Driving over a speed bump
B Pumping the brakes
C Setting the parking brake, releasing the service brakes, and gently trying to move the vehicle in low gear
D Releasing the parking brake on a flat surface and tugging gently against it

Correct answer: C

The standard test: set parking brakes, gently apply throttle in low gear; if the vehicle moves, the parking brake is not holding.

Question 22 of 25

Which of the following is NOT part of a pre-trip inspection?

A Testing the service and parking brakes
B Checking the engine compartment
C Walking around the vehicle and checking lights
D Adjusting the trailer brakes individually

Correct answer: D

Adjusting brakes is a maintenance task done by qualified personnel, not a pre-trip step. The driver checks for proper operation, not adjustment.

Question 23 of 25

Which is true about communicating in heavy traffic?

A Tap the horn lightly or flash lights to signal your presence
B Make eye contact only when stopped
C Honk loudly to warn other drivers
D Never communicate; just drive

Correct answer: A

A light tap of the horn or a brief headlight flash communicates your presence without startling others. A loud, prolonged horn can provoke aggressive responses.

Question 24 of 25

The maximum allowable on-duty driving time after 8 consecutive hours off duty is:

A 16 hours
B 10 hours
C 14 hours
D 11 hours

Correct answer: D

After 10 hours off duty, a property-carrying driver may drive up to 11 hours, within a 14-hour on-duty window.

Question 25 of 25

The most important hand position on the steering wheel is:

A 10 and 2 (or 9 and 3)
B One hand at 12
C 12 and 6
D Both hands at the bottom

Correct answer: A

A balanced grip at 10-and-2 or 9-and-3 gives the most control. One-handed and bottom-of-wheel positions reduce reaction time.

Study tips for the Illinois General Knowledge exam

The General Knowledge portion of the Illinois CDL exam is graded out of the bank of questions the Illinois Secretary of State draws from each year. While the exact bank is not published, every question is sourced from the General Knowledge chapter of the Illinois CDL handbook, which itself is derived from the FMCSA Model Commercial Driver's License Manual. That means studying our practice tests, reading the corresponding handbook chapter, and re-reading the parts you got wrong is genuinely the most efficient route to a first-time pass.

Most successful applicants follow a simple cycle: take the practice test cold, write down every question you missed, open the matching chapter of the official Illinois handbook, re-read the section that contains the right answer, then re-take the practice test 24 to 48 hours later. The 24-hour delay matters — sleep is when your brain commits new information to long-term memory, and CDL knowledge questions reward that kind of consolidated learning rather than cramming.

Pay particular attention to questions that include qualifier words like always, never, only, primary, or most. CDL test writers love to flip the right answer with a single qualifier. When two answer choices look almost identical, pay attention to the verb (is it must, should, or may?) and to any numbers (14 days, 100 air miles, 8 hours, 70/8 split). On endorsement tests in particular, watch for trick framing where a true statement about a different endorsement is offered as the "correct" answer to a question that is actually about General Knowledge.

Test-day logistics matter too. Bring photo ID, your Social Security card or birth certificate, your medical examiner's certificate (DOT card), and proof of state residency if you haven't already submitted those documents. The Illinois Secretary of State will not let you sit for the knowledge exam without your documentation, and most offices charge an additional fee for re-attempts. Arrive early — the wait at most CDL testing offices runs 30 to 60 minutes — and silence your phone before the exam begins.

Finally, keep your General Knowledge fundamentals sharp even when you're focused on the General Knowledge exam. Many states administer multiple knowledge tests in a single sitting, and questions on weight definitions (GVWR, GCWR, GAWR), stopping distance, and the pre-trip inspection routine show up across endorsements. If you're unsure on the basics, sit a fresh Illinois General Knowledge practice test before scheduling the real exam.

Next steps

Missed more than four questions? Re-read the General Knowledge study guide and the matching chapter in the official Illinois CDL handbook. Then come back and re-take the test. Once you can score 22 of 25 or higher on three runs in a row, you're in good shape to schedule the real exam at your local Illinois Secretary of State office.

Already comfortable with this endorsement? Drill another: IL Air Brakes · IL Combination Vehicles · IL Hazardous Materials · IL Passenger · IL School Bus · IL Tank Vehicle · IL Doubles / Triples

New to the CDL process in Illinois? Read How to apply for a CDL in Illinois for the document checklist and step-by-step timeline.