CDL General Knowledge Practice Test
This is a free 15-question sampler on the CDL general knowledge test, written by the StudyPDF team. It covers the pre-trip inspection, backing and turning, space and speed management, seeing hazards, skid control, cargo securement, fires and the alcohol rules, mixing multiple choice, select all that apply and fill in the blank. Air brakes, combination vehicles and hazardous materials are separate tests, so they are not on this one. Answer all 15 questions, then check your score and read the explanation for every question.
Federal rules require a commercial vehicle to carry a set of emergency equipment. Which set is correct?
All Work & Citizenship quizzes
- Practice test · 15 questions
CDL Practice Test
- Practice test · 15 questions
CDL Air Brakes Practice Test
- Practice test · 15 questions
CDL Combination Vehicles Practice Test
Now make your own
Upload your prep book, slides or notes, or just tell Bo what you want to learn. You do not need a document to start.
All 15 questions at a glance
Prefer to read before you play? Every question in the sampler is listed below. Answers and explanations stay collapsed until you open them.
1. Federal rules require a commercial vehicle to carry a set of emergency equipment. Which set is correct?
- A. A first aid kit, a tire pressure gauge and a flashlight
- B. Two red flags, jumper cables and a spare fuel filter
- C. Three red reflective warning triangles, at least one charged and rated fire extinguisher, and spare electrical fuses if the vehicle uses them
- D. A wheel chock, a reflective vest and a spare drive belt
Show answer and explanation
Answer: C. Three red reflective warning triangles, at least one charged and rated fire extinguisher, and spare electrical fuses if the vehicle uses them
You check this equipment during the in-cab step of the seven step inspection, before you check the lights and start the walkaround. Warning devices mark your vehicle for other drivers when you have to stop on the shoulder, the extinguisher has to be charged and rated for what you haul, and fuses only apply if the vehicle uses them, since many use circuit breakers instead. A first aid kit and a flashlight are smart to carry, but they are not what the rule asks for.
2. You are on the walkaround part of your pre-trip inspection. Which findings mean the vehicle should not go out until it is repaired?
Select all that apply.
- A. A steering axle tire measuring 3/32 inch of tread
- B. A recapped tire on a drive axle
- C. A cut in a tire deep enough to show the body ply underneath
- D. A rear tire measuring 5/32 inch of tread
- E. A crack running across the rim of a wheel
Show answer and explanation
Answer: A. A steering axle tire measuring 3/32 inch of tread, C. A cut in a tire deep enough to show the body ply underneath, E. A crack running across the rim of a wheel
Front tires carry the steering and the most load per tire, so they need more tread than the rest, and 3/32 inch is under the minimum. Any tire with fabric, body ply or belt material showing is unsafe no matter how much tread is left, and a cracked or bent rim can let a tire come off the wheel. A recapped tire is legal on a drive axle, and 5/32 inch on a rear tire is above the minimum, so neither of those grounds the vehicle.
3. Complete the sentence.
Federal rules set a minimum tread depth of _____ inch on the tires of the steering axle and _____ inch on every other tire.
Options for blank 1: 2/32, 4/32, 6/32, 8/32
Options for blank 2: 1/32, 2/32, 4/32
Show answer and explanation
Answer: 4/32, 2/32
Measure in a major groove, not on a rib or a wear bar, and check more than one spot, since uneven wear can leave one shoulder legal and the other bald. Tread depth is one of the few numbers the general knowledge test asks you for directly. Uneven wear is also a clue to something else, so a front tire wearing on one edge usually means an alignment or inflation problem rather than a tire problem.
4. You have to back into a space and you can choose which side to back toward. What is the safer choice and why?
- A. Back toward the driver side, because you can see that side of the vehicle directly as well as in the mirror
- B. Back toward the passenger side, because that mirror is convex and shows a wider view
- C. Either side is equally safe as long as you use both mirrors
- D. Back toward the passenger side, because oncoming traffic sees you sooner
Show answer and explanation
Answer: A. Back toward the driver side, because you can see that side of the vehicle directly as well as in the mirror
Backing toward the passenger side is blind side backing, and it forces you to trust one mirror for a whole quarter of the vehicle. A wider mirror view does not make up for losing the direct look. Whichever side you use, get out and walk the area first, back slowly, and if you have a helper, agree on hand signals in advance and keep the helper somewhere you can see in the mirror, with a clear signal that means stop.
5. You are making a tight right turn at an intersection in a long vehicle. What is the correct technique?
- A. Swing wide to the left first so the rear has room, then complete the turn
- B. Move to the center of the road before the turn so nobody can come up on your right
- C. Turn from the left lane whenever the corner looks tight
- D. Keep the rear of the vehicle close to the curb and swing wide only as you complete the turn
Show answer and explanation
Answer: D. Keep the rear of the vehicle close to the curb and swing wide only as you complete the turn
The rear wheels follow a tighter path than the front wheels, which is called off tracking, so a long vehicle has to turn wide somewhere. Doing it at the end keeps the gap on your right closed. If you swing left first, a driver behind you may read it as a left turn or slip into the space on your right and get squeezed against the curb. If you cannot make the turn without crossing into the oncoming lane, wait until that lane is clear rather than starting the turn and hoping.
6. Complete the sentence.
Below 40 mph, allow one second of following distance for every _____ feet of vehicle length. At 55 mph, a 60 foot combination should therefore keep at least _____ seconds of space ahead.
Options for blank 1: 5, 10, 15, 20
Options for blank 2: 4, 5, 6, 7
Show answer and explanation
Answer: 10, 7
Sixty feet divided by ten gives six seconds, and above 40 mph you add one more second, which makes seven. To count it, watch the vehicle ahead pass a fixed object such as a sign or an overpass shadow, then count the seconds until the front of your vehicle reaches the same point. Add more space on wet or icy roads, at night, and any time you are following something you cannot see past.
7. Total stopping distance is the sum of which three distances?
- A. Perception distance, braking distance and skid distance
- B. Perception distance, reaction distance and braking distance
- C. Reaction distance, braking distance and following distance
- D. Sight distance, reaction distance and braking distance
Show answer and explanation
Answer: B. Perception distance, reaction distance and braking distance
Perception distance is how far you travel from the moment your eyes see a hazard until your brain recognizes it. Reaction distance is how far you travel from that recognition until your foot reaches the brake. Braking distance is how far the vehicle travels once the brakes are actually working. The model manual puts all three together at 55 mph on dry pavement with good brakes at roughly 335 feet, which is longer than a football field, and that is why looking far ahead buys you more than any braking technique.
8. Which statements about speed and stopping are true?
Select all that apply.
- A. Braking distance grows in step with speed, so twice the speed means twice the distance
- B. Doubling your speed roughly quadruples the braking distance
- C. An empty truck can need a longer stopping distance than a loaded one
- D. Wet pavement makes no difference as long as the tires have legal tread
- E. Posted curve speeds are set with cars in mind, so a heavy vehicle often has to go slower than the sign
Show answer and explanation
Answer: B. Doubling your speed roughly quadruples the braking distance, C. An empty truck can need a longer stopping distance than a loaded one, E. Posted curve speeds are set with cars in mind, so a heavy vehicle often has to go slower than the sign
Braking distance grows with the square of speed, so the jump from 20 to 40 mph costs you about four times the distance, not two. An empty truck feels nimble but has less weight pressing its tires down, and its brakes and suspension are built for a load, so it can skid and stop poorly. On wet roads the usual guidance is to cut your speed by about a third, on packed snow by about half, and on ice to slow to a crawl and get off the road as soon as you safely can.
9. How far ahead should you be looking while you drive?
- A. About 2 to 4 seconds ahead, since that is where a hazard would actually reach you
- B. Only as far as your headlights reach, so you do not miss what is close
- C. About 12 to 15 seconds ahead, which is roughly a quarter mile at highway speed
- D. About 30 seconds ahead, which is roughly a mile at highway speed
Show answer and explanation
Answer: C. About 12 to 15 seconds ahead, which is roughly a quarter mile at highway speed
Twelve to fifteen seconds is about one city block in town and about a quarter mile on the highway. At that range you still have time to slow smoothly or change lanes instead of braking hard. Looking far ahead does not mean staring at one point, so keep scanning near and far and check your mirrors every five to eight seconds, more often when traffic is heavy or you are near other vehicles.
10. Why should you shift into a low gear before you start down a long, steep grade?
- A. Because engine braking then helps hold your speed, and the transmission may not let you get into a low gear once you are already rolling fast
- B. Because a low gear increases air flow through the radiator and stops the engine overheating
- C. Because the higher the gear, the harder the service brakes hold
- D. Because a low gear locks the drive axles together and gives you extra traction
Show answer and explanation
Answer: A. Because engine braking then helps hold your speed, and the transmission may not let you get into a low gear once you are already rolling fast
Gravity keeps adding speed the whole way down, so the gear does the steady work and the brakes are there to supplement it, not to carry the descent alone. Brakes that are held on continuously heat up and fade, and by the time you notice that they are fading you have very little left. Your safe speed depends on the weight, the length and steepness of the grade, the road surface and the weather, so read the signs at the top and know where the escape ramps are before you need one.
11. Complete the sentence.
Cargo held down with tiedowns needs at least one tiedown for every _____ feet of cargo, and no load, however short, may have fewer than _____ tiedowns.
Options for blank 1: 5, 8, 10, 12
Options for blank 2: one, two, three
Show answer and explanation
Answer: 10, two
The count is only half of it, since the combined working load limit of the tiedowns has to be at least half the weight of the cargo they hold. Securement is also the driver's job even when someone else loaded the trailer, so inspect the load before you leave, again within the first 50 miles, and then every 150 miles or every 3 hours, whichever comes first. Weight that sits too high raises the center of gravity and makes a rollover in a curve or an exit ramp much easier.
12. A fire starts in the wiring behind your dashboard. Which extinguisher is right, and what must you not do?
- A. A class A extinguisher, and do not aim at the base of the flames
- B. Water, and do not open the hood
- C. A class D extinguisher, and do not shut the engine off
- D. A B:C or A:B:C extinguisher, and do not put water on an electrical fire
Show answer and explanation
Answer: D. A B:C or A:B:C extinguisher, and do not put water on an electrical fire
Class A covers ordinary combustibles like wood, paper and cloth, class B covers burning liquids such as fuel and grease, class C covers electrical fires and class D covers burning metals. Water conducts electricity and it spreads a liquid fire instead of putting it out, so the B:C rating is what matters here. Before you use it, pull well off the road away from buildings and other vehicles, shut the engine off, call for help, then stay upwind, aim at the base of the flames and use short bursts. Only fight a fire that is small enough for you to handle.
13. You are approaching a railroad crossing with no gate and a clear view of the track. What should you do?
- A. Shift down as you reach the rails so you can accelerate away quickly
- B. Stay in one gear the whole way across, and do not start across unless you can clear the far side without stopping
- C. Stop on the near rail, look both ways, then move on
- D. Speed up so you spend less time on the tracks
Show answer and explanation
Answer: B. Stay in one gear the whole way across, and do not start across unless you can clear the far side without stopping
Changing gears on the crossing is how drivers end up stalled on the rails, so pick your gear before the tracks and hold it. A tractor and trailer needs roughly 14 to 15 seconds to clear a single track, longer for a double track, so you have to see room for the whole vehicle on the far side before you start. Watch for raised or humped crossings if you drive anything low slung, and remember that buses and some placarded loads have to stop at every crossing whether or not a train is coming.
14. Which statements about skids are true?
Select all that apply.
- A. Most skids happen because the vehicle was going too fast for the conditions
- B. Black ice is easy to spot because it turns the pavement white
- C. Pressing harder on the accelerator is the quickest way to straighten out a skid
- D. In a drive wheel skid caused by braking too hard, you stop braking, let the wheels roll again, then countersteer
- E. In a front wheel skid the vehicle keeps going straight no matter which way you turn the steering wheel
Show answer and explanation
Answer: A. Most skids happen because the vehicle was going too fast for the conditions, D. In a drive wheel skid caused by braking too hard, you stop braking, let the wheels roll again, then countersteer, E. In a front wheel skid the vehicle keeps going straight no matter which way you turn the steering wheel
Skids are mostly a speed problem, whether that is braking too hard, turning too fast or accelerating too hard on a slick surface. A drive wheel skid ends when the wheels start rolling again, so you release the brake or ease off the accelerator first, then steer back the other way as the rear comes into line. A front wheel skid is different, because the steering tires have already lost their grip, so the only cure is to let the vehicle slow until they bite again. Black ice is a thin clear layer and the road just looks wet, so watch your mirror arms and antenna for ice as a warning.
15. Which statement about alcohol and a CDL is correct?
- A. A CDL holder is held to the same blood alcohol limit as any other driver in the state
- B. Coffee, fresh air or a cold shower will bring a blood alcohol level down faster
- C. Alcohol only affects a driver once the legal limit has been passed
- D. Driving a commercial vehicle with a blood alcohol concentration of 0.04 or higher is a violation, and any detectable alcohol puts the driver out of service
Show answer and explanation
Answer: D. Driving a commercial vehicle with a blood alcohol concentration of 0.04 or higher is a violation, and any detectable alcohol puts the driver out of service
The commercial limit of 0.04 is half the 0.08 that applies to ordinary drivers in most states, and detectable alcohol below 0.04 still gets you placed out of service for 24 hours. Drivers are also barred from drinking within four hours of going on duty. Judgment, reaction time and vision all get worse well before any legal limit is reached, and only time removes alcohol from the body, so nothing you drink or do speeds it up.
What the CDL general knowledge test actually covers
Every commercial driver license applicant takes the general knowledge test, whatever class of vehicle they plan to drive. It is a written test given by your state, and it is built from your state's own CDL manual, which you can download free from the state driver license agency. Most state manuals are lightly edited versions of the AAMVA model manual, so the content is close to the same everywhere. The number of questions and the passing score are set by the state, not by a national body. Eighty percent is the most common passing mark, but the only number worth trusting is the one printed in your state manual or on your state's licensing website. You have to pass this test before any endorsement test and before you can book the skills test.
The content comes from a few chapters of that manual. Driving safely is the largest: vehicle inspection, basic control, shifting, seeing and communicating, managing space and speed, spotting hazards, emergency maneuvers, skid control and recovery, night, winter, hot weather and mountain driving, railroad crossings, accident procedures and fires. Transporting cargo safely adds weight, balance and securement. Then come driver fitness, the alcohol and drug rules, and the basic hours of service limits for property carrying drivers, currently 11 hours of driving after 10 consecutive hours off duty, inside a 14 hour window. Federal hours rules do get revised, so confirm them against the current FMCSA rule rather than an old handout.
What varies by state is everything around the content: the fee, how many attempts you get, how long you wait between retakes, whether the test is on paper or a touchscreen, and whether a reader is available. Air brakes, combination vehicles, tankers, doubles and triples, passenger, school bus and hazardous materials are all separate tests with their own questions, so general knowledge is the first written test and not the whole written exam. Federal entry level driver training rules have also applied since 2022 and change when you can sit the skills test and the hazmat knowledge test. Check your state page for the current order of steps.
How to use this sampler
These 15 questions stay inside the general knowledge material and go deeper than a mixed CDL sampler would. They ask why a rule exists, not only what it says: why you back toward the driver side, why an empty truck can be harder to stop than a loaded one, why the low gear goes in before the grade and not halfway down it. That reasoning is what keeps the numbers in your head on test day, and it is what the road asks of you afterward. Air brake, coupling and placard questions are deliberately missing here, because they belong to their own tests and their own pages, linked below. If you are studying for more than one written test, run those samplers in separate sessions rather than mixing everything together.
Take it in one sitting with the manual closed, then read the explanation for every question, including the ones you got right. Treat a wrong answer as a chapter to reread rather than a single fact to memorize. If you missed the following distance question and the stopping distance question, the topic to go back to is space management as a whole, not those two numbers. A short list of numbers really is worth learning by heart, because the test asks them straight out: the two minimum tread depths, the one second per 10 feet following rule, the three parts of stopping distance, one tiedown per 10 feet of cargo with a floor of two, and the 0.04 alcohol level. Most of the rest you can reason your way to.
Then read the manual itself. It is free, you can get through it in a few evenings, and the real questions come out of it. Where a number you read somewhere else disagrees with your state manual, the manual wins, because your state wrote the test. This sampler also cannot cover everything that is fair game. Night driving, hot weather checks, mountain driving, distracted and aggressive driving, where your warning devices go after you stop on the shoulder and what to do at the scene of a crash are all on the test and none of them are in these 15 questions. A quick way to find those gaps is to skim the chapter headings and mark every one you could not summarize in a sentence.
How StudyPDF builds full practice tests from your own materials
Fifteen questions can show you where you are shaky. They cannot get you ready on their own, and a generic question bank does not know which state manual you are studying or what your training school puts the most weight on.
StudyPDF works from your material instead. You upload your state CDL manual, the handouts from your training school or the notes you took in class, and Bo, the study agent, builds full-length practice tests from those exact pages. Every question is grounded in your material, and every explanation points to where the answer came from, so you can go straight to the page when something looks off. You can regenerate fresh tests as often as you like, narrow them to one area such as cargo securement or space management, and track which topics you keep missing.
You do not need a document to start. If you have nothing to upload, name a topic instead, for example the seven step inspection or skid recovery, and Bo writes a practice test from that. Starting is free.
Written by the StudyPDF team. Last updated 2026-08-19.