Free CDL Practice Test: 100 Questions and Answers

This free CDL practice test has 100 questions and answers, each with a short explanation.

It follows the main parts of a commercial driver’s license knowledge test: General Knowledge (40 questions), Air Brakes (20), Combination Vehicles (15), HazMat and Tankers (15) and Passengers and School Bus (10).

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Pick an answer to get instant feedback and learn why the other options are wrong.

Important: these are original practice questions written to help you study. They are not real state test questions, and rules differ by state. Study your own state’s CDL manual and follow its numbers, because states may differ on details such as age limits, test length and passing scores.

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Select an answer to see instant feedback. Your score updates as you go, and the section scores appear when you finish. Study notes, the answer key and FAQs are below the quiz.

Quick jump: General Knowledge (40)Air Brakes (20)Combination Vehicles (15)HazMat & Tankers (15)Passengers & School Bus (10)

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CDL General Knowledge (40 Questions)

1. Which license class is needed to drive a combination of vehicles with a gross combination weight rating of 26,001 pounds or more, if the vehicle being towed is heavier than 10,000 pounds?

A.Class BB.Class CC.Class DD.Class A

Answer: D. Class A covers combinations rated 26,001 pounds or more where the towed unit is over 10,000 pounds. Class B is a single heavy vehicle, and Class C covers smaller vehicles that carry passengers or placarded hazardous materials.

2. A straight truck with a gross vehicle weight rating of 28,000 pounds that tows a 6,000-pound trailer needs which class of CDL?

A.Class AB.Class CC.Class BD.No CDL is required

Answer: C. Class B covers a single vehicle rated 26,001 pounds or more, towing a unit of 10,000 pounds or less. The trailer here is under the 10,000-pound limit, so the truck’s weight sets the class.

3. Which vehicle requires a Class C CDL?

A.A tractor-trailer with a 30,000-pound combination rating and a 12,000-pound trailerB.A van designed to carry 16 passengers including the driverC.A dump truck with a 30,000-pound gross vehicle weight ratingD.A pickup truck pulling a 5,000-pound trailer on a public road

Answer: B. Class C covers vehicles that do not meet Class A or B but are designed to carry 16 or more people including the driver, or that carry placarded hazardous materials. It also needs a passenger or hazmat endorsement.

4. In general, how old must a driver be to operate a commercial vehicle across state lines under federal rules?

A.16 years oldB.21 years oldC.18 years oldD.19 years old

Answer: B. Federal rules require drivers who cross state lines, or who haul hazardous materials, to be at least 21. Many states allow 18-year-olds to drive commercially inside the state. Check your state’s rules.

5. What is the first step of a seven-step pre-trip inspection?

A.Vehicle overview: review the last inspection report and look the vehicle overB.Check the brakes with the engine running and the air system fully chargedC.Test the air system leakage rate with the engine switched offD.Check the lights, reflectors and signals from the front of the vehicle

Answer: A. The inspection starts with a vehicle overview. You look at the vehicle as you approach it and review the previous driver vehicle inspection report to see what was repaired.

6. What is the minimum tread depth that federal rules require for steer-axle tires?

A.2/32 of an inchB.6/32 of an inchC.1/32 of an inchD.4/32 of an inch

Answer: D. Steer tires need at least 4/32 of an inch of tread in any major groove. Other tires need at least 2/32 of an inch.

7. With power steering, how much steering wheel play is the most you should have before the wheels begin to move?

A.About 30 degrees, or about 6 inches on a 20-inch wheelB.About 5 inches of movement at the rim of a 20-inch steering wheelC.About 10 degrees, or about 2 inches on a 20-inch wheelD.About 1 degree, with no movement at the rim of the wheel

Answer: C. More than about 10 degrees of play means the steering linkage may be worn or loose. That is a defect you must have repaired.

8. On a vehicle with hydraulic brakes, you press the brake pedal firmly and it slowly sinks toward the floor. What does that most likely mean?

A.The brakes are working normally and the pedal is just settling inB.The brake pads are brand new and are still wearing in properlyC.There is a leak or other problem in the brake system, and you should not driveD.The brake lights are out and the bulbs need to be replaced

Answer: C. A pedal that slowly sinks under steady pressure points to a leak or a failing master cylinder. Get it repaired before driving.

9. When must a commercial driver wear a seat belt?

A.Only when driving on the highway at speeds over 55 mphB.Whenever driving the vehicleC.Only when the vehicle is carrying a load over a set weightD.Only when driving at night or in bad weather conditions

Answer: B. Seat belts must be worn at all times while driving a commercial motor vehicle. They are a federal requirement and your best protection in a crash.

10. What does the backing rule “GOAL” stand for?

A.Get Out And LookB.Go Over All LanesC.Gear Option And LightsD.Give Others A Lane

Answer: A. Before you back up, get out and look at the path, including overhead and side clearances. Then back slowly and use a helper if you can.

11. When you have a choice, which way should you back a large vehicle?

A.Toward the passenger side, using the right mirror and a guideB.Straight back only, with no turning of the wheels at any pointC.Toward whichever side is closer to the curb or the dockD.Toward the driver’s side, so you can see the path

Answer: D. Backing toward the driver’s side lets you see the rear and the path through the side window and mirror. Backing toward the blind side is much riskier.

12. What should you do before entering a curve?

A.Brake hard in the middle of the curve to scrub off speedB.Speed up slightly so that the weight settles on the drive axleC.Shift down to a lower gear in the middle of the curveD.Slow down to a safe speed before the curve

Answer: D. Reduce speed before the curve, because braking or shifting inside it can cause a skid or a rollover. Posted curve speeds are for cars. Trucks often need to go slower.

13. A truck is 40 feet long and traveling at 55 mph. At minimum, how many seconds of following distance should the driver keep in good conditions?

A.2 secondsB.3 secondsC.5 secondsD.8 seconds

Answer: C. Allow one second for every 10 feet of vehicle length below 40 mph. At 40 mph and above add one more second. A 40-foot truck needs 4 seconds plus 1, or 5 seconds.

14. A 60-foot combination vehicle is traveling at 30 mph. What is the minimum following distance in seconds?

A.3 secondsB.6 secondsC.7 secondsD.4 seconds

Answer: B. Below 40 mph you allow one second for every 10 feet of length, so 60 feet is 6 seconds. You add one more second only at 40 mph and above.

15. How far ahead should you look while driving?

A.About 12 to 15 seconds aheadB.About 2 to 3 seconds aheadC.Only at the vehicle directly in frontD.About 1 minute ahead

Answer: A. Looking 12 to 15 seconds ahead gives you time to see and handle hazards. That is about a city block at low speeds or about a quarter mile on the highway.

16. How often should you check your mirrors while driving?

A.Every 5 to 8 secondsB.Only when changing lanesC.Once every minuteD.Only when backing

Answer: A. Check mirrors regularly, every 5 to 8 seconds, and before changes of speed or direction. Also look for blind spots and for objects close to your vehicle.

17. What happens to braking distance when your speed doubles?

A.It doubles, because braking distance rises in direct proportion to speedB.It stays the same, because the brakes are the sameC.It becomes about half, because the tires grip harder at speedD.It becomes about four times as great

Answer: D. Braking distance increases with the square of speed. At twice the speed you need roughly four times the distance to stop.

18. What are the three parts of total stopping distance?

A.Perception distance, signal distance and following distanceB.Reaction distance, braking distance and parking distanceC.Perception distance, reaction distance and braking distanceD.Braking distance, steering distance and load distance

Answer: C. You first see the hazard (perception), then move your foot to the brake (reaction), and then the vehicle slows (braking). All three add up to the total.

19. Compared with a fully loaded truck, an empty truck usually stops…

A.In a shorter distance, because it has less weight to slow downB.In a longer distance, because it has less tractionC.In the same distance, because the brakes work the same wayD.In a shorter distance, because the brakes grab harder when empty

Answer: B. Brakes are designed to work with a heavy load. An empty truck can have less traction and may lock up its wheels or bounce, so it often needs more distance to stop.

20. What should you do if your vehicle begins to hydroplane?

A.Brake as hard as you can so the tires bite through the waterB.Ease off the accelerator and push in the clutch, avoiding hard brakingC.Speed up slightly to cross the water film quickly and regain gripD.Turn the wheel sharply toward the shoulder to find traction

Answer: B. Hydroplaning means tires ride on a film of water. Slow down gradually and avoid heavy braking or sudden steering until the tires regain traction.

21. If the drive wheels begin to skid because of over-braking, what should you do?

A.Release the brake, and steer in the direction you want the vehicle to goB.Brake harder, so the wheels slow down and regain traction fasterC.Turn the wheel opposite to the direction you want to goD.Accelerate firmly to pull the vehicle out of the skid

Answer: A. Take your foot off the brake to let the wheels turn again, then steer where you want to go. Counter-steer smoothly if the rear swings, but do not oversteer.

22. Which gear should you use going down a steep grade?

A.A higher gear than you would use going up, to keep speed downB.Neutral, to let the engine rest and save fuel on the way downC.Any gear, then rely on the brakes alone for the entire gradeD.The same gear you would use to go up the grade

Answer: D. Use the same gear you would use going uphill, and brake with steady pressure when needed. Never shift into neutral on a downgrade, and shift before you start down.

23. What are truck escape ramps designed for?

A.Giving drivers a place to rest and park for the nightB.Weighing trucks that may be over the legal limitC.Stopping vehicles whose brakes have failed or overheated on a long downgradeD.Letting slow vehicles pull aside so traffic can pass them

Answer: C. Escape ramps use gravel or an uphill grade to stop a runaway vehicle. Use them if you cannot control your speed, and do not wait until it is too late.

24. What does “overdriving your headlights” mean?

A.Using high beams in fog so you can see farther aheadB.Driving with only one headlight working on the vehicleC.Driving so fast that you cannot stop within the distance your headlights showD.Turning the headlights on too early before it gets dark

Answer: C. At night your stopping distance must be shorter than the area your headlights light up. Low beams show less distance than high beams, so you may need to slow down.

25. An oncoming driver’s headlights are blinding you at night. What should you do?

A.Look directly at the oncoming lights to judge their distanceB.Look toward the right edge of the road and slow downC.Flash your high beams back at the other driverD.Close one eye and keep your speed the same until they pass

Answer: B. Looking at the right edge of the road keeps you on course without staring at the glare. Slow down and do not retaliate with your high beams.

26. What is the only cure for fatigue while driving?

A.SleepB.Drinking coffeeC.Opening the windowD.Turning up the radio

Answer: A. Caffeine, fresh air and music do not fix real sleepiness. If you feel drowsy, stop at a safe place and rest.

27. Which is a good practice for night driving?

A.Use high beams all the time, even when others are approachingB.Keep your windshield a little dirty to cut down on glareC.Drive as fast as you do in daylight, because roads are emptierD.Slow down and increase your following distance

Answer: D. At night you see less, so drive slower, keep a larger space cushion, and keep the windshield, lights and mirrors clean.

28. What is the blood alcohol concentration at or above which a CDL holder is considered to be driving under the influence in a commercial vehicle?

A.0.08 percentB.0.02 percentC.0.10 percentD.0.04 percent

Answer: D. The federal limit for commercial vehicle drivers is 0.04 percent. A state may also charge a CDL holder at 0.08 percent in any vehicle.

29. What is the disqualification period for a first conviction for driving a commercial vehicle under the influence?

A.60 days, or 120 days if hauling hazardous materialsB.Six months, or one year if hauling hazardous materialsC.One year, or three years if hauling hazardous materialsD.Five years, or ten years if hauling hazardous materials

Answer: C. A first offense means a one-year disqualification, and it is three years if you were transporting hazardous materials. A second offense means a lifetime disqualification. Refusing a test counts the same way.

30. Two serious traffic violations within three years will result in what disqualification?

A.No disqualificationB.60 daysC.One yearD.30 days

Answer: B. Two serious violations within three years carry a 60-day disqualification, and three carry 120 days. Serious violations include texting, speeding 15 mph or more over the limit, reckless driving and following too closely.

31. What is the penalty for a first railroad-highway grade crossing violation by a CDL driver?

A.A 60-day disqualificationB.A warning onlyC.A one-year disqualificationD.A 10-day suspension

Answer: A. A first offense is a 60-day disqualification, and a second within three years is 120 days. A third offense within three years is one year.

32. Driving at what speed over the posted limit counts as a serious traffic violation?

A.15 mph or moreB.5 mph or moreC.10 mph or moreD.25 mph or more

Answer: A. Speeding 15 mph or more above the limit is a serious violation. Other examples are reckless driving, improper lane changes and following too closely.

33. What is the federal rule about hand-held phones while driving a commercial vehicle?

A.They may be used in light traffic if you keep your eyes on the roadB.They may be used with one hand while the other stays on the wheelC.They may be used in a stopped lane of traffic, but not textingD.They may not be used while driving, and texting is prohibited

Answer: D. Hand-held mobile phone use and texting are prohibited while driving a commercial vehicle. Use hands-free equipment where allowed, and stop in a safe place for calls.

34. After starting a trip, when should you first check your cargo and its securement?

A.Only when you arrive at the destination, before unloadingB.After 500 miles, because loads rarely shift before thatC.Within the first 50 miles, then every 150 miles or 3 hoursD.Only if the load looks loose or you hear it moving

Answer: C. Check cargo within the first 50 miles, then after every 150 miles or three hours of driving, and after any break. Loads can shift and straps can loosen.

35. Where should heavy cargo be placed for the best stability?

A.High up, for better balance and easier unloadingB.Low, and centered over the axlesC.Along one side of the trailer, to leave room for the aisleD.At the very back, near the doors, for quick access

Answer: B. A low, centered load gives a low center of gravity and reduces the risk of rollover. A high or uneven load makes the vehicle top-heavy.

36. A vehicle is following you too closely. What is the best response?

A.Brake hard to scare the driver into backing offB.Increase your following distance ahead and avoid sudden stopsC.Speed up to build distance, even if it is above the limitD.Slow down quickly to force the tailgater to pass you

Answer: B. Make more room ahead so you can slow smoothly. That gives the tailgater more time to react and reduces the chance of a rear-end crash.

37. When making a right turn in a large vehicle, what should you do?

A.Keep the rear of the vehicle close to the curbB.Swing wide to the left first so the trailer can followC.Turn from the center lane and cut across at the cornerD.Speed up to clear the turn before traffic closes in

Answer: A. Starting wide to the left or leaving a gap at the curb invites other drivers to squeeze in. Keep the back of the vehicle near the curb and turn smoothly.

38. When a commercial vehicle is stopped on the shoulder, what should the driver do?

A.Leave the lights off to save the battery while you waitB.Stay in the left lane with the engine runningC.Park with the front wheels turned left and stay in the cabD.Turn on the four-way flashers and put out warning devices

Answer: D. Turn on the flashers right away and place warning triangles at the required distances. Warning devices alert other drivers to your stopped vehicle.

39. For how long can a medical examiner’s certificate be valid, at the longest?

A.Up to 6 monthsB.Up to 5 yearsC.Up to 24 monthsD.For life

Answer: C. A certificate can last up to 24 months, and a shorter period may be given for certain health conditions. You must carry or have on file a valid certificate.

40. By how much should you reduce speed on wet roads?

A.By about 5 mph onlyB.By about two-thirdsC.By about one-thirdD.You do not need to reduce speed

Answer: C. Reduce speed by about one-third on wet roads and by half or more on packed snow. Also increase your following distance.

Air Brakes Endorsement (20 Questions)

41. At about what pressure does the air compressor governor stop pumping air (cut-out)?

A.About 60 psiB.About 125 psiC.About 45 psiD.About 200 psi

Answer: B. The governor typically cuts out at about 125 psi and the compressor stops pumping. It starts pumping again at about 100 psi.

42. At about what pressure does the governor start the compressor pumping again (cut-in)?

A.About 100 psiB.About 125 psiC.About 20 psiD.About 150 psi

Answer: A. The cut-in pressure is about 100 psi. If the pressure keeps falling, you must stop and fix the problem.

43. A low air pressure warning must come on before the air pressure drops below what level?

A.20 psiB.100 psiC.125 psiD.60 psi

Answer: D. The warning device, usually a light and buzzer, must activate before pressure falls below 60 psi. If you see or hear it, stop safely and find the cause.

44. At what range of air pressure do the spring brakes begin to apply automatically?

A.60 to 80 psiB.100 to 125 psiC.5 to 10 psiD.20 to 45 psi

Answer: D. Spring brakes apply when pressure drops to about 20 to 45 psi, and the parking brake valve will pop out. Do not rely on them to stop, and stop before pressure gets there.

45. With a fully charged system, engine off and brakes released, what is the maximum air loss allowed in one minute for a single vehicle?

A.1 psiB.5 psiC.2 psiD.10 psi

Answer: C. A single vehicle may lose no more than 2 psi in one minute. Combination vehicles may lose 3 psi in one minute.

46. What is the maximum air loss in one minute for a two-vehicle combination during the leakage test with the brakes released?

A.2 psiB.3 psiC.6 psiD.1 psi

Answer: B. A two-vehicle combination may lose up to 3 psi per minute in the static leakage test. More than that means a leak that needs repair.

47. During the applied-pressure leakage test, with the brake pedal pressed firmly, what is the maximum loss in one minute for a single vehicle?

A.3 psiB.1 psiC.8 psiD.12 psi

Answer: A. Hold the pedal down for one minute. A single vehicle may lose 3 psi, and a combination vehicle may lose 4 psi.

48. How quickly should a dual air system build pressure from 85 to 100 psi at operating RPM?

A.Within 45 secondsB.Within 5 secondsC.Within 3 minutesD.Within 10 minutes

Answer: A. Dual air systems should build from 85 to 100 psi within 45 seconds at fast idle. A slower buildup may mean a compressor or leak problem.

49. Why must air tanks be drained regularly?

A.To increase air pressure and make the brakes strongerB.To cool the compressor so it does not overheatC.To lower the governor setting and cut fuel useD.To remove water and oil that can freeze or damage the brakes

Answer: D. Water and oil collect in the tanks and can freeze in cold weather or get into brake parts. Drain them at the end of each day, unless the system has automatic drains.

50. What is the most common cause of brake fade?

A.Low tire pressure on the drive axleB.Using the engine brake too often on a downgradeC.Excessive heat from overusing the brakes on a long downgradeD.Cold weather that makes the brake fluid thick

Answer: C. Heat builds in the drums and the brakes lose stopping power. Use a lower gear and engine braking so the service brakes do not do all the work.

51. What are the shape and color of the parking brake control valve?

A.A red octagonB.A yellow diamondC.A blue circleD.A green square

Answer: B. The parking brake valve is a yellow diamond. The trailer air supply valve is a red octagon.

52. What is the main benefit of an antilock braking system (ABS)?

A.It always shortens the stopping distance on any surfaceB.It helps you keep control and steer while braking hardC.It removes the need to inspect the brakes before a tripD.It increases the air pressure in the system

Answer: B. ABS prevents wheel lockup so you can keep steering. It does not always shorten stopping distance, and you still need to keep a safe following distance.

53. What is brake lag?

A.The delay while air travels through the lines to apply the brakesB.The time it takes to fill the air tanks after startingC.A leak in the brake chamber that is slowly venting airD.The time needed for the engine to warm up before moving

Answer: A. Brake lag is about half a second with air brakes, because air must travel through the lines. Allow for it in your stopping distance.

54. If the low air warning comes on while you are driving, what should you do?

A.Keep going to the next stop, then check the systemB.Pump the brake pedal quickly to build up the pressureC.Turn off the engine and coast to a stopD.Stop safely right away and find the problem

Answer: D. If air pressure keeps dropping, the spring brakes may apply suddenly. Stop in a safe place and repair the problem before you continue.

55. At about what pressure does the air system safety valve open?

A.60 psiB.125 psiC.150 psiD.20 psi

Answer: C. The safety valve protects the tank and opens at about 150 psi. If it keeps blowing off, the governor needs repair.

56. During the slack adjuster check, how much movement of the pushrod when you pull hard is too much?

A.More than about 5 inchesB.Any movement at allC.More than about one inchD.More than about a foot

Answer: C. With the brakes released, pull hard on the pushrod. If it moves more than about an inch, the brake is out of adjustment.

57. How do you test the parking brake?

A.Release the parking brake and coast slowly to a stopB.Apply the parking brake, put the vehicle in a low gear and gently pull against itC.Press the brake pedal and check that the brake lights come onD.Turn off the engine for five minutes and watch the gauges

Answer: B. Seat belt on, parking brake set, low gear, and gently try to move. The vehicle should not move.

58. If a non-ABS vehicle begins to skid when you brake hard, which technique can be used?

A.Controlled braking: brake as hard as you can without locking the wheelsB.Pump the pedal quickly and repeatedly until it stopsC.Take your foot off the pedal and hold the wheel steadyD.Turn the steering wheel back and forth while braking

Answer: A. In controlled braking you apply the brakes as hard as you can without locking the wheels and keep steering. If they lock up, release and reapply.

59. What is the purpose of an alcohol evaporator on an air brake system?

A.To cool the brake drums on a long downgradeB.To clean the air tanks and remove oil and rustC.To increase the air pressure in the systemD.To reduce the risk of ice in the system in cold weather

Answer: D. The evaporator adds alcohol to the air to lower the chance of ice in the valves and lines. Check the alcohol level daily in cold weather.

60. What is a dual air brake system?

A.Two compressors working together to fill a single air tankB.One system for the brakes and a separate one for the hornC.An air brake system combined with a hydraulic systemD.Two separate air systems, a primary and a secondary, using one set of controls

Answer: D. A dual system has two independent air systems for safety, so if one fails the other can still stop the vehicle. You have to watch both gauges.

Combination Vehicles (15 Questions)

61. Before backing under a trailer, how should the fifth wheel be prepared?

A.Tilted up toward the front, with the jaws closedB.Left dry so the plate grips the trailer betterC.Tilted down toward the rear, with jaws open and the plate lubricatedD.Tilted to the left, with the jaws open and no lubricant

Answer: C. The fifth wheel should be tilted down toward the rear, the locking jaws open and the plate greased. The kingpin can then slide in and lock.

62. After backing under the trailer, how do you test the coupling?

A.Back up quickly under the trailer to test the lockB.Pull forward gently with the trailer brakes onC.Check only the air lines and the electrical cordD.Look only at the landing gear to see that it is raised

Answer: B. Gently pull the tractor forward against the locked trailer brakes. If the trailer moves with the tractor, the coupling is secure.

63. What should you see when you look at the fifth wheel after coupling?

A.No gap between the upper and lower plates, and the jaws closed around the shankB.A large gap between the plates, which is normal with a good lockC.The jaws closed around the head of the kingpinD.The kingpin sitting above the plate and not visible at all

Answer: A. The jaws must close around the shank, not the head, with no gap between the plates. A gap means the trailer may not be locked to the tractor.

64. After connecting the air lines, what should you do before the trailer is released?

A.Build air pressure and push in the trailer air supply valveB.Drain all the tanks, then turn off the engineC.Pull out the tractor protection valve to release the trailerD.Release the landing gear and start driving at once

Answer: A. Charge the system and push in the red octagon trailer air supply valve to release the trailer spring brakes.

65. Before uncoupling a tractor from the trailer, what must you do with the landing gear?

A.Leave it up, because the tractor will keep the trailer levelB.Raise it fully before you disconnect anythingC.Disconnect it from the trailer and store it in the cabD.Lower it until it supports the weight of the trailer

Answer: D. Lower the landing gear so it carries the trailer’s weight, then disconnect the air lines and electrical cord and release the fifth wheel.

66. After releasing the fifth wheel lock, how far should you pull the tractor forward at first?

A.Completely clear of the trailer, so you can inspect itB.Not at all, because you only release the lockC.Until the fifth wheel clears the trailer frame, stopping with the tractor frame still under the trailerD.Just a few feet, in reverse, to test the lock

Answer: C. Stopping with the tractor frame under the trailer helps protect it if the landing gear fails. Then inspect before pulling out fully.

67. Which factor is the most important for avoiding a rollover on a curve?

A.Shifting to a high gear before the curveB.Reducing speed before the curveC.Using the trailer hand brake in the middle of the curveD.Making a sudden steering move at the entry to the curve

Answer: B. Rollovers often happen at speeds under the posted limit for a curve or ramp. Slow down before you reach it, and avoid braking or steering hard in the curve.

68. What is rearward amplification?

A.A louder horn heard at the rear of the combinationB.The tendency of the last trailer to swing more than the tractor in a quick moveC.A stronger brake force applied to the rear axleD.Extra air pressure in the rear tank that lifts the trailer

Answer: B. Also called crack-the-whip. In a sudden lane change the rear trailer swings out more, and it can tip over. Doubles and triples are the most affected.

69. How does a high center of gravity affect a truck?

A.It makes it more likely to roll overB.It makes it more stable in curves and in a sudden turnC.It shortens the braking distance on dry roadsD.It has no effect on stability if the load is secured

Answer: A. The higher the load’s center of gravity, the easier it is for the vehicle to tip in a curve or sudden turn. Keep loads low and centered.

70. When pulling doubles, where should the heavier trailer be placed?

A.At the back, as the last trailer in the combinationB.Anywhere, because the order does not matterC.On the converter dolly, just ahead of the second trailerD.Behind the tractor, as the first trailer

Answer: D. The lighter trailer goes in the rear, which reduces rearward amplification and the risk of a rollover.

71. Why should you not use the trailer hand brake to park?

A.It can damage the brake chamber and the pushrodB.It uses too much air from the supply tankC.Air can leak out and release the brakes, so the vehicle could rollD.It is not strong enough to hold a loaded trailer

Answer: C. Air will eventually leak and the brakes will release. Use the parking brakes and chock the wheels, and use the hand valve only for testing.

72. What most commonly causes a jackknife?

A.A low tire on the trailer axleB.Light cargo carried near the rear of the trailerC.Locking the tractor drive wheels from over-braking on a slippery roadD.A full fuel tank on the tractor

Answer: C. When the drive wheels lock they lose traction and the trailer pushes the tractor around. Brake early and gently, and keep the vehicle straight.

73. What is the job of the tractor protection valve?

A.To increase the air pressure that is sent to the trailerB.To close and save the tractor’s air if the trailer breaks away or has a major leakC.To drain the water and oil from the air tanksD.To control the trailer lights and the turn signals

Answer: B. If the air pressure drops to about 20 to 45 psi, the valve closes automatically. That helps keep the tractor’s air supply and brakes working.

74. How should the air lines and electrical cord be connected between tractor and trailer?

A.Supported, with enough slack for turns and no draggingB.Pulled tight, so they cannot move and wearC.Left on the ground, so they are out of the wayD.Taped to the landing gear so that they do not swing

Answer: A. Make sure the glad hands are sealed and locked, and the lines are supported with some slack so they do not snag or get cut.

75. Before driving away after coupling, what must be true of the landing gear?

A.It must be lowered halfwayB.It can be left downC.It must be removedD.It must be fully raised

Answer: D. Raise the landing gear fully and secure the crank handle. Landing gear left down can be torn off or can cause a crash.

HazMat & Tankers (15 Questions)

76. For which materials is a placard required regardless of the amount?

A.Any material under 100 pounds, even in small packagesB.Materials of Class 9, such as miscellaneous hazardous materialsC.None of them, because placards are never required in small amountsD.Table 1 materials, such as explosives and poison gas

Answer: D. Table 1 materials need a placard in any amount. Table 2 materials need a placard when the total of all such materials is 1,001 pounds or more.

77. At what total gross weight of Table 2 materials is a placard required?

A.100 poundsB.500 poundsC.1,001 pounds or moreD.5,000 pounds

Answer: C. Table 2 materials, such as flammable liquids and corrosives, need placards when the aggregate gross weight is 1,001 pounds or more.

78. Where should shipping papers be kept when the driver is in the cab?

A.In the glove box, where it is protected from the weatherB.Within immediate reach of the driver wearing a seat belt, or on the seat or in a door pouch when out of the vehicleC.In the sleeper berth, behind the driver’s seatD.With the dispatcher or at the shipper’s office

Answer: B. Shipping papers must be within reach of the belted driver, and when you leave the cab they go on the driver’s seat or in the door pouch. Emergency responders look there first.

79. What is hazard Class 3?

A.Flammable liquidsB.ExplosivesC.Radioactive materialsD.Corrosives

Answer: A. Class 3 is flammable liquids such as gasoline. Class 1 is explosives, Class 7 is radioactive and Class 8 is corrosives.

80. What is hazard Class 8?

A.CorrosivesB.Flammable gasesC.OxidizersD.Poison

Answer: A. Class 8 means corrosive materials, such as battery acid. Oxidizers are Class 5.

81. What is required to get a hazmat endorsement?

A.Only a driving test in a vehicle with a placardB.A 10-year clean driving record and a medical cardC.A Class C license and a hazmat training certificate onlyD.A knowledge test and a TSA security threat assessment

Answer: D. You must pass the hazmat knowledge test and a TSA background check, including fingerprints. The CDL itself is issued by your state.

82. When is a hazmat vehicle considered attended?

A.When the driver is anywhere in the building or the truck stopB.When the engine is running and the doors are unlockedC.When the driver is within 100 feet and has a clear view of itD.When the doors are locked and the keys are not in the ignition

Answer: C. Attended means the driver is awake, within 100 feet of the vehicle and has a clear view. Otherwise the vehicle must be attended by a qualified person.

83. How close to a vehicle with flammable liquids may a person smoke?

A.Within 5 feetB.Not within 25 feetC.Within 10 feetD.No restriction

Answer: B. No smoking or open flames within 25 feet of a vehicle that carries flammable materials. Fumes can ignite.

84. Where should a vehicle with hazardous materials not be parked?

A.On a flat lot with no slopeB.Within 300 feet of an open fireC.In the shade, away from the sunD.Next to another truck at a rest area

Answer: B. Do not park within 300 feet of open fires, and avoid bridges, tunnels, buildings and crowded places except for brief stops.

85. On which sides of the vehicle must placards be displayed?

A.Both sides, the front and the rearB.The front only, so that the driver can see themC.The driver’s side only, so that they are visible at the curbD.The rear only, so that drivers behind can see them

Answer: A. Placards go on all four sides so that anyone approaching can see them. They must be clean and readable.

86. What is the first thing to use in a hazmat emergency to find out about the material?

A.A tire gauge and the trip logB.The trip log and the vehicle inspection reportC.The CB radio and the shipper’s phone numberD.The shipping papers and the Emergency Response Guidebook

Answer: D. Check the shipping papers for the identification number and look it up in the Emergency Response Guidebook. Then call for help and keep people away.

87. What do baffles in a liquid tank do?

A.Remove all of the surge, front to back and side to sideB.Cool the liquid as it moves through the tankC.Reduce the front-to-back surge, but not the side-to-side surgeD.Increase the pressure inside the tank to hold the load steady

Answer: C. Baffles have holes that slow the surge from front to back, but they do not stop the liquid from moving side to side. Take turns slowly.

88. Which tank type has the greatest liquid surge?

A.A tank with baffles, which slow the movement of the liquidB.A tank with bulkheads, which divide it into compartmentsC.A smooth-bore tank, which has no bafflesD.An empty tank, because there is nothing to move

Answer: C. Smooth-bore tanks, like many food tanks, have nothing to slow the surge. Be especially careful with braking and curves.

89. What is outage in a tank vehicle?

A.The empty weight of the tank without any liquidB.Empty space left in the tank for the liquid to expandC.The pressure of the gas that is above the liquidD.The amount of fuel in the tractor’s tank

Answer: B. Liquids expand as they warm up, so do not fill a tank to the top. The amount of room needed depends on the liquid.

90. Which CDL endorsement allows a driver to haul hazardous materials in a tank vehicle?

A.X, the combined tank and hazmat endorsementB.P, the passenger endorsementC.S, the school bus endorsementD.T, the double and triple trailer endorsement

Answer: A. N is for tank vehicles and H is for hazmat. The X endorsement combines both.

Passengers & School Bus (10 Questions)

91. At a railroad crossing, how far from the nearest rail should a bus stop?

A.Between 1 and 5 feetB.Between 100 and 150 feetC.On the tracksD.Between 15 and 50 feet

Answer: D. Stop 15 to 50 feet from the nearest rail, open the door, look and listen, and make sure the way is clear before you cross.

92. What should you do at a railroad crossing before crossing?

A.Speed up and cross quickly if no train is visibleB.Shift gears on the tracks if you need more powerC.Close the door and window and rely on your mirrorsD.Open the door and window, look and listen, and do not shift gears on the crossing

Answer: D. Open the door and window to hear a train, and look both ways. Never change gears on the tracks, since you could stall.

93. What is the standee line on a bus?

A.The line for ticket holders at the terminalB.A line at the rear door where passengers wait to exitC.A line that passengers may not stand in front ofD.A line that marks the area reserved for luggage

Answer: C. No passenger may stand forward of the standee line, which is behind the driver. It keeps the driver’s view and the entry area clear.

94. How far around a school bus is the danger zone?

A.1 footB.10 feetC.20 feetD.50 feet

Answer: B. The danger zone is the 10 feet around the bus, where children are most at risk. Make sure they are visible before you move.

95. When should a school bus driver turn on the amber (yellow) warning lights?

A.100 to 300 feet before the stop, depending on state lawB.After the bus stops and the doors openC.Never, because the red lights are enoughD.Only at night or when it is raining

Answer: A. Amber lights warn drivers that the bus is about to stop. Rules vary by state, so check your manual.

96. When should a school bus driver turn on the red lights and stop arm?

A.After the bus is stopped and ready for loading or unloadingB.While the bus is still moving toward the stopC.Only at railroad crossings and drawbridgesD.Before the amber lights, at least 500 feet away

Answer: A. Red lights and the stop arm are used when the bus is stopped and children are getting on or off. Use them only when stopped.

97. What should a bus driver do about baggage and cargo?

A.Put it in the doorway so that it is easy to reachB.Stack it in the aisle to leave the seats freeC.Leave it loose on the seats so it is easy to findD.Keep it secured and out of the aisle and exits

Answer: D. Cargo must not block exits, aisles or the driver’s view. In an emergency passengers need a clear path.

98. What should a bus driver do about an unruly passenger?

A.Argue with the passenger while you continue to driveB.Stop on the highway shoulder and leave the busC.Stop in a safe place, and deal with it only when parked or call for helpD.Ignore the passenger completely until the end of the route

Answer: C. Do not let the situation distract you while driving. Stop in a safe place and handle it or call for help.

99. A driver needs a passenger (P) endorsement for a vehicle designed to carry how many people?

A.5 or moreB.16 or more, including the driverC.9 or moreD.30 or more

Answer: B. A P endorsement is needed for vehicles designed for 16 or more people including the driver. A school bus driver also needs an S endorsement.

100. When inspecting a bus, what should you check on the emergency exits?

A.That they are locked, to stop passengers using themB.That they open and close properly and that their warning signs are in placeC.That they are painted the same color as the busD.That they are blocked, so that nobody opens them by accident

Answer: B. Test each emergency exit and check the signs, buzzers and lights. Emergency exits must be usable and never blocked.

Your Score

Section	Score

About the CDL Knowledge Tests

The Federal Motor Carrier Safety Administration (FMCSA) explains that most drivers must obtain a commercial driver's license through their home state, and that it is illegal to hold a license from more than one state. Applicants must pass both skills and knowledge testing. FMCSA does not issue licenses, so your state licensing agency sets the details, including test questions, fees and passing scores. Special endorsements may be required for double or triple trailers, tank trucks, hazardous materials and passenger vehicles.

Your CDL class depends on the vehicle you will drive:

CDL class	What it covers
Class A	A combination of vehicles with a gross combination weight rating of 26,001 pounds or more, where the towed unit is over 10,000 pounds
Class B	A single vehicle with a gross vehicle weight rating of 26,001 pounds or more, towing a unit of 10,000 pounds or less
Class C	A vehicle that does not meet Class A or B, but is designed to carry 16 or more people including the driver, or carries placarded hazardous materials

CDL Endorsements at a Glance

Each endorsement adds a knowledge test, and some need a skills test as well. Air brakes work a little differently: there is no separate endorsement letter. If you do not pass the air brakes knowledge test, or test in a vehicle without air brakes, your license is restricted so that you cannot drive vehicles with air brakes. Your state manual explains the exact rules.

Endorsement	Letter	Needed for
Double/triple trailers	T	A truck with double or triple trailers
Tank vehicle	N	A truck with a tank
Hazardous materials	H	A truck carrying placarded hazardous materials
Tank and hazmat	X	Both a tank and hazardous materials
Passenger	P	A vehicle designed to carry 16 or more people including the driver
School bus	S	A school bus

What Is in This Practice Test

Section	Questions	What it focuses on
CDL General Knowledge	40	Vehicle inspection, speed management, basic vehicle control and night driving
Air Brakes	20	Dual air systems, brake fade and inspecting system components
Combination Vehicles	15	Coupling and uncoupling, and preventing trailer rollovers
HazMat and Tankers	15	Containment rules, placarding and handling liquid surge
Passengers and School Bus	10	Loading and unloading zones and railroad crossing rules

How to Use This Practice Test

Pick an answer for each question. You get instant feedback and the scoreboard keeps count.
Read every explanation, including for questions you answered correctly.
Check your section scores at the end, then reread that part of your state manual.
Memorize the numbers. Following distances, air pressures, leakage limits and placard weights come up again and again.
Use the "Retry missed" button after a day or two.
Take only the sections you need. Everyone takes General Knowledge. Add Air Brakes, Combination Vehicles, HazMat, Tankers or Passengers only if you want those endorsements or need to drive those vehicles.
Confirm every figure with your own state manual before test day.

Score Yourself

Most states require 80 percent on each knowledge test, but check your state. Use the ranges below as a study guide for this page.

90 to 100: excellent. You are ready to move on to your state's own practice questions.
80 to 89: good. Review the questions you missed and the sections where you scored lowest.
70 to 79: keep studying. Reread the manual sections for your weakest areas.
Below 70: study the manual again, then retake the test in a few days.

Getting your CDL? Once you pass, put it to work with our CDL truck driver resume sample, CDL driver cover letter sample and CDL Class A cover letter sample.

Answer Key

Use this key to score yourself quickly. The explanations above tell you why.

Q	A	Q	A	Q	A	Q	A	Q	A
1	D	21	A	41	B	61	C	81	D
2	C	22	D	42	A	62	B	82	C
3	B	23	C	43	D	63	A	83	B
4	B	24	C	44	D	64	A	84	B
5	A	25	B	45	C	65	D	85	A
6	D	26	A	46	B	66	C	86	D
7	C	27	D	47	A	67	B	87	C
8	C	28	D	48	A	68	B	88	C
9	B	29	C	49	D	69	A	89	B
10	A	30	B	50	C	70	D	90	A
11	D	31	A	51	B	71	C	91	D
12	D	32	A	52	B	72	C	92	D
13	C	33	D	53	A	73	B	93	C
14	B	34	C	54	D	74	A	94	B
15	A	35	B	55	C	75	D	95	A
16	A	36	B	56	C	76	D	96	A
17	D	37	A	57	B	77	C	97	D
18	C	38	D	58	A	78	B	98	C
19	B	39	C	59	D	79	A	99	B
20	B	40	C	60	D	80	A	100	B

Frequently Asked Questions

Click a question to see the answer.

How many questions are on the CDL general knowledge test?

It depends on the state. The test is multiple choice, and most states require a passing score of 80 percent. Check your state's CDL manual or licensing agency for the number of questions and the passing score.

Is there a separate air brakes endorsement?

No. Air brakes is a knowledge test, not an endorsement with its own letter. If you do not pass it, or take your skills test in a vehicle without air brakes, your CDL gets a restriction that bars you from driving air-brake vehicles.

Which endorsements do I need?

It depends on what you drive. FMCSA lists double or triple trailers, tank vehicles, hazardous materials and passenger vehicles as the common ones. School bus drivers also need a school bus endorsement. Ask your employer which ones the job requires.

Do all CDL drivers take the General Knowledge test?

Yes. The General Knowledge test is the base test for every CDL applicant, and endorsement tests are added on top of it. Class A applicants also take the Combination Vehicles test.

Are these real CDL test questions?

No. They are original practice questions written for study, and your state test will use its own questions. The topics and numbers match what CDL manuals teach, but follow your state's manual if it differs.

What happens after I pass the knowledge test?

In general you get a commercial learner's permit, then complete required training and take the skills test, which has a pre-trip inspection, basic control and a road test. Entry-level driver training rules apply to many first-time applicants, so ask your state licensing agency.

What is a good score on this practice test?

Aim for at least 80 percent in every section, since most states require that on the real test. Review any section where you score lower.

Conclusion

Practice questions work best when you read the explanation for every answer, track your weak sections and retest them. Work through all 100 questions, retry the ones you missed and reread your state's CDL manual before test day. Once you have your license, update your resume and cover letter to show it. Good luck.