Free Illinois DMV CDL — General Knowledge Practice Test 2026
The Illinois CDL — General Knowledge knowledge test has ~50 questions, and you need ~40 correct (80%) to pass. Practice free with questions written from the official Illinois driver handbook — every one has a clear explanation, and you can retake as often as you like with no sign-up.
Content reviewed against official driver handbooks · August 12, 2026
What's on the Illinois written test
The Illinois CDL — General Knowledge knowledge test has ~50 questions; you need ~40 correct (80%) to pass.
Based on the official Illinois exam format — always confirm current details with your state DMV.
Practice by topic
Focus on one area at a time — each topic has its own set of Illinois practice questions.
Speed limits, turning and signaling rules, headlight and seat-belt requirements, and the everyday laws every driver must follow.
Following distance, scanning, blind spots, using your lights, and the habits that prevent crashes and keep you in control.
Driving safely around motorcycles, bicycles, large trucks, pedestrians, and school buses — and knowing who has the right of way.
Blood alcohol limits, zero-tolerance and implied-consent laws, and how alcohol and drugs — legal or not — affect your driving.
Choosing a safe speed, keeping a space cushion, adjusting for weather and traffic, and understanding stopping distance.
What to do when things go wrong — brake failure, tire blowouts, skids, and stalling on railroad tracks.
The point system, license suspension, provisional-license rules, insurance requirements, and other licensing basics.
How to pass the first time
- Read the official Illinois driver handbook at least once before test day.
- Practice by topic to find your weak spots, then fix them.
- Take full-length practice tests until you pass comfortably every time.
- Read every explanation — understanding beats memorizing.
Illinois CDL — General Knowledge test — frequently asked questions
How many questions are on the Illinois CDL — General Knowledge test?
The Illinois CDL — General Knowledge knowledge test has ~50 questions, and you need ~40 correct (80%) to pass. Our practice tests mirror that format.
How many questions can I miss on the Illinois CDL — General Knowledge test?
You can miss up to ~10 of the ~50 questions and still pass — you need ~40 correct, which is 80%.
Can I retake the practice test?
Yes — practice as often as you like, completely free. The questions and answer choices are shuffled each time.
Can I take the Illinois practice test in Spanish?
Yes. Every question here is available in English and Spanish — switch languages anytime. Many states also offer the real knowledge test in languages other than English; confirm what Illinois offers with your DMV.
Can I practice on my phone?
Yes. The practice tests work in any mobile or desktop browser — no app or sign-up needed — so you can study anywhere.
Are these the real DMV test questions?
No. Our questions are original, written from the current official Illinois driver handbook to match the real test's topics and style. We are not affiliated with any DMV or government agency.
What's the best way to study?
Read the Illinois driver handbook, practice by topic to target weak areas, and finish with full-length tests until you consistently pass.
Other Illinois practice tests
Take the CDL — General Knowledge test in another state
Every Illinois question is written from the official Illinois driver handbook and checked against its current edition. DMV Test Free is a free, independent study resource — not affiliated with any DMV or government agency. About DMV Test Free
Illinois CDL — General Knowledge questions with answers
20 sample questions from the Illinois CDL — General Knowledge question bank — each with the correct answer, a short explanation, and the section of the official handbook it comes from.
Show all 20 questions with answers
1. If your vehicle does not have self-canceling turn signals, what must you remember after a turn?
Correct answer: Turn the signal off after the turn
Remember to turn the signal off after completing the turn if it does not cancel itself. A signal left blinking can confuse other drivers about your intentions.
Source: Illinois CDL Guide — Sec. 2.5, Signal Your Intentions
2. Before you drive a truck that has a dual air-brake system, what minimum pressure should both systems reach?
Correct answer: At least 100 psi in both systems
Allow the air compressor to build at least 100 psi in both the primary and secondary systems before you drive a dual-air-brake vehicle.
3. Using a commercial vehicle to commit a felony involving the manufacture or distribution of a controlled substance results in what?
Correct answer: A lifetime disqualification
When a commercial or non-commercial vehicle is used to manufacture, distribute, or dispense a controlled substance, the driver faces a permanent, lifetime loss of commercial driving privileges.
4. What is the safest way to handle your speed when approaching a curve in a large vehicle?
Correct answer: Slow down before the curve, then ease through it
Slow to a safe speed before entering the curve and pick a gear that lets you accelerate slightly through it. Braking inside the curve can lock the wheels and start a skid.
5. If your vehicle begins to hydroplane, what is the correct response?
Correct answer: Release the accelerator and push in the clutch
Ease off the accelerator and push in the clutch so the wheels can turn freely and the vehicle slows. Do not brake, because braking can make you lose control on the water film.
6. Which headlights should you use to see best when driving in fog?
Correct answer: Low beams and fog lights
Use low-beam headlights and fog lights in fog, even in daytime. High beams reflect off the fog and actually make it harder to see.
7. What is the safe assumption to make about hearing a train at a crossing?
Correct answer: You should not count on hearing a train
Do not expect to hear a train. Engine and road noise, and the train's own angle, can keep you from hearing it, so you must rely on looking carefully in both directions.
8. What must a driver do when a train is approaching so closely that it creates an immediate hazard?
Correct answer: Stop before the crossing
You must stop when an approaching train is plainly visible and in hazardous proximity to the crossing. Failing to stop is a grade-crossing violation with escalating penalties.
9. If you have to stop on a road or its shoulder, how soon must your emergency warning devices be placed?
Correct answer: Within 10 minutes
When you stop on a roadway or shoulder, you must put out your warning devices within 10 minutes so approaching drivers get enough notice of your stopped vehicle.
Source: Illinois CDL Guide — Sec. 2.5, Communicating Your Presence
10. By operating on Illinois highways, a commercial driver has legally agreed to do what?
Correct answer: Submit to chemical testing for blood-alcohol concentration
Under the state's implied-consent rule, anyone driving on public roads has already consented to chemical testing that measures blood-alcohol concentration if lawfully requested. Refusing that testing carries its own disqualification.
Source: Illinois CDL Guide — Sec. 1.5, Alcohol/Drug Regulations
11. A placarded hazardous-materials vehicle must display at least how many placards?
Correct answer: Four identical placards
A placarded load must show at least four identical placards, one readable from each of the four directions around the vehicle.
12. What should you do with your turn signal before changing lanes?
Correct answer: Turn the signal on before changing lanes
Put your turn signal on before you change lanes, then change slowly and smoothly so a driver you did not notice has a chance to react.
13. Who is responsible for making sure a commercial vehicle is not overloaded?
Correct answer: The driver of the vehicle
The driver is responsible for recognizing overloads and poorly balanced weight, whether or not they personally loaded the vehicle. An overload can damage the vehicle and make it unsafe.
14. What is the minimum age required to drive a bus designed to seat 16 or more people?
Correct answer: 21 years old
A driver must hold a CDL and be at least 21 years old to operate a vehicle built to seat at least 16 people, including the driver.
Source: Illinois CDL Guide — Sec. 4, Transporting Passengers Safely
15. Why do commercial vehicles need extra care about space to the sides?
Correct answer: They are wide and fill nearly the whole lane
Commercial vehicles are often wide and fill most of a lane, leaving little room on either side. Keep centered in your lane and avoid driving alongside others when you can.
16. The most common skid comes from the rear wheels losing traction. How do you correct a drive-wheel braking skid?
Correct answer: Stop braking and countersteer
Stop braking so the rear wheels can roll again, then countersteer — turn the wheel quickly back the other way as the vehicle straightens so you do not swing into a skid the opposite direction.
17. About how far ahead can you typically see with low-beam headlights?
Correct answer: About 250 feet
Low beams light the road for roughly 250 feet ahead, while high beams reach about 350 to 500 feet. Match your speed to whichever distance you can actually see.
18. At a passive railroad crossing with no lights or gates, what is your responsibility?
Correct answer: Look for a train and judge whether it is safe to cross
A passive crossing gives no active warning, so you must recognize it, look for any approaching train, and decide whether there is enough clear space to cross safely.
19. A driver causes a crash while distracted by a phone. What consequence does Illinois law allow?
Correct answer: Criminal penalties and possible jail time
Beyond ordinary traffic penalties, a crash that results from distracted driving may expose the driver to criminal charges and possible jail time.
20. Why should you not rely on your taillights to warn traffic when you are parked at night?
Correct answer: Taillights can be mistaken for a moving vehicle
Drivers have crashed into parked vehicles because glowing taillights made them think the vehicle was moving normally. Use the four-way flashers to show you are stopped.
Source: Illinois CDL Guide — Sec. 2.5, When Parked at the Side of the Road