CDL General Knowledge Sample Questions

Questions from each area of the CDL General Knowledge test. Pick an answer to see whether you're right, how everyone else did, and why.

CDL General Knowledge Test exam guide

1 Safe operations regulations

Your truck tows a trailer rated at 14,000 pounds GVWR, and the GCWR is 30,000 pounds. You need:

  1. a Class B CDL
  2. a Class C CDL
  3. a Class A CDL

Answer: C, a Class A CDL. A combination is Class A when its GCWR is 26,001 pounds or more and the towed unit is rated over 10,000 pounds GVWR. Both are true here. Driving it with a lower class is a serious violation (49 CFR 383.91, 383.51).

Alcohol harms judgment before other skills. Because of this, a drinking driver:

  1. usually notices his poor balance first.
  2. often cannot tell that he is impaired.
  3. usually notices his blurred vision first.

Answer: B, often cannot tell that he is impaired.. Alcohol first dulls the part of the brain that handles judgment and self-control. So a drinker often feels fine and does not see that he is drunk (CDL manual 2.22).

2 Safe vehicle control systems

A retarder on a truck helps you by:

  1. stopping the drive wheels from skidding on ice.
  2. giving the service brakes more stopping power.
  3. slowing the vehicle, which cuts brake use and brake wear.

Answer: C, slowing the vehicle, which cuts brake use and brake wear.. A retarder slows the vehicle on its own. You need the service brakes less, so they wear less and stay cooler. (CDL manual 2.3)

When a retarder is switched on, it applies braking force:

  1. on all wheels, whenever you press the brake pedal.
  2. on the drive wheels, whenever you take your foot fully off the accelerator.
  3. on the front wheels, whenever you shift to a lower gear.

Answer: B, on the drive wheels, whenever you take your foot fully off the accelerator.. A retarder that is on slows only the drive wheels. It starts working as soon as you lift your foot all the way off the accelerator. (CDL manual 2.3.4)

3 CMV safety control systems

Your truck must carry a fire extinguisher. Federal rules say it must also carry:

  1. a spare tire.
  2. a first aid kit.
  3. 3 reflective triangles.

Answer: C, 3 reflective triangles.. Federal rules require a fire extinguisher and warning devices for a stopped truck. The warning devices are a set of 3 reflective triangles, or else 6 or more fusees. (49 CFR 393.95)

You set each mirror to show a small part of your own vehicle. This helps you:

  1. judge where other vehicles are in the mirror.
  2. see into the blind spots beside your vehicle.
  3. None of the above.

Answer: A, judge where other vehicles are in the mirror.. Part of your own truck in the mirror gives you something fixed to compare with. That makes it easier to tell where other vehicles and objects are. (CDL manual 2.4.2)

4 Basic control

Your truck has a manual transmission. How do you pull away on a hill without rolling back?

  1. Hold the clutch all the way in until your right foot leaves the brake.
  2. Partly let the clutch out before your right foot leaves the brake.
  3. Take your right foot off the brake, then let the clutch out quickly.

Answer: B, Partly let the clutch out before your right foot leaves the brake.. Start to engage the clutch before you lift your foot off the brake. The engine then holds the truck as the brake lets go, so it does not roll back. (CDL manual 2.2.1)

You are making a tight right turn in a long truck. The cab clears the curb. Why might the rear wheels still hit it?

  1. The rear of the truck leans toward the curb as you turn.
  2. The rear wheels swing out wider than the front wheels do.
  3. The rear wheels take a shorter path, inside the path of the front wheels.

Answer: C, The rear wheels take a shorter path, inside the path of the front wheels.. In a turn, the rear wheels cut inside the line the front wheels took. This is called off-tracking, and it lets the rear strike a curb or car that the cab missed. (CDL manual 2.7.6)

5 Shifting

Your truck has a synchronized manual transmission. Do you need to double clutch to change gears?

  1. Yes, it is needed in any heavy truck transmission.
  2. Yes, it is needed when you shift down.
  3. No, it is not needed with this kind of transmission.

Answer: C, No, it is not needed with this kind of transmission.. No. You do not need to double clutch with a synchronized transmission. Most heavy trucks with the other kind, an unsynchronized one, do need it. (CDL manual 2.3)

As you drive a manual-shift truck over railroad tracks, you should:

  1. stay in one gear until you clear them.
  2. shift up so you clear them faster.
  3. shift down once the front wheels reach them.

Answer: A, stay in one gear until you clear them.. A missed shift on the rails could stall your truck right on the crossing. Choose your gear before the tracks and hold it until you are across. (CDL manual 2.15.5)

6 Backing

Why is backing a truck always dangerous?

  1. Reverse gears give the engine too little power.
  2. You can't see everything behind the truck.
  3. The brakes are weaker when moving backward.

Answer: B, You can't see everything behind the truck.. Backing is risky because you cannot see everything behind a large vehicle. Avoid backing whenever you can. (CDL manual 2.2)

Before you back with a helper, you should do all of these EXCEPT:

  1. plan for the helper to guide you by voice instead of hand signals.
  2. decide where the helper will stand so you can see them.
  3. agree on the hand signal that means stop.

Answer: A, plan for the helper to guide you by voice instead of hand signals.. In the cab, engine noise can drown out a helper's voice. Before backing, agree on hand signals you both know, including one for stop, and keep the helper where you can see them. (CDL manual 2.2)

7 Visual search

Looking 12 to 15 seconds ahead also means you should:

  1. watch the vehicle right in front of you most of the time.
  2. keep your eyes fixed on the road far ahead.
  3. shift your eyes between things close by and far away.

Answer: C, shift your eyes between things close by and far away.. Looking far ahead does not mean ignoring what is close. Good drivers keep moving their eyes between near and far (CDL manual 2.4.1).

Each time you check a mirror while driving, you should:

  1. hold your eyes on it for a few seconds to judge speeds.
  2. glance at it, then look back at the road ahead.
  3. study it until you know what each car behind is doing.

Answer: B, glance at it, then look back at the road ahead.. While you look at a mirror, the truck keeps moving and you are not watching ahead. Take quick glances and switch back to the road. (CDL manual 2.4)

8 Communication

You have just finished a right turn, and your signal is still flashing. You should:

  1. leave it on for one more block.
  2. leave it on until you reach normal speed.
  3. turn it off right away.

Answer: C, turn it off right away.. Once the turn is done, switch the signal off if it does not cancel by itself. A signal left on tells other drivers you are about to turn again, which can cause a crash. (CDL manual 2.5.1)

Your vehicle must stop at a railroad crossing ahead. What should you do while stopping?

  1. Watch for traffic behind you and turn on your four-way flashers.
  2. Flash your high beams and sound your horn to warn the train.
  3. Turn on your right turn signal and stop as quickly as you can.

Answer: A, Watch for traffic behind you and turn on your four-way flashers.. Drivers behind you may not expect a stop at the tracks. Check your mirrors, slow down gradually, use a pullout lane if there is one, and turn on your four-way flashers. (CDL manual 2.15.4)

9 Speed management

If a lot of water covers the road, your truck can hydroplane at speeds as low as:

  1. 55 mph.
  2. 30 mph.
  3. 45 mph.

Answer: B, 30 mph.. Hydroplaning is not only a highway-speed problem. With a lot of water on the road, it can start at about 30 mph, so slow down in heavy rain. (CDL manual 2.6)

You are driving a truck on a road you have never used. Besides the speed limit, base your speed on:

  1. how late you are running and how much fuel you can save.
  2. road grip, curves, how far you can see, traffic, and hills.
  3. the speed of the fastest cars and trucks around you.

Answer: B, road grip, curves, how far you can see, traffic, and hills.. A safe speed depends on the conditions: traction, curves, how far you can see, traffic, and hills. Even at or under the posted limit, you must slow down when these call for it. (CDL manual 2.6)

10 Space management

When you enter traffic in a heavily loaded truck, you need a gap that is:

  1. much larger than a car's, because your truck speeds up slowly.
  2. about the same as a car's, because traffic will slow for a truck.
  3. smaller than when empty, because the extra weight improves traction.

Answer: A, much larger than a car's, because your truck speeds up slowly.. A big truck picks up speed slowly and takes up a lot of road, so it needs a much bigger gap than a car. The heavier the load, the slower it speeds up, so leave even more room. (CDL manual 2.7)

Your single-axle tractor pulls a long trailer whose landing gear is set for tandem axles. At a raised crossing, the trailer may:

  1. sway too far sideways and roll over on the tracks.
  2. drag on the rails and leave the rig stuck on the tracks.
  3. rock off the fifth wheel and come uncoupled from the tractor.

Answer: B, drag on the rails and leave the rig stuck on the tracks.. On a single-axle tractor, a trailer set up for a tandem-axle tractor rides low at the landing gear. On a raised crossing, it can catch on the rails and get stuck. (CDL manual 2.15)

11 Night operation

To get ready for a night trip, you should be well rested and:

  1. do a full inspection that checks every light and reflector.
  2. do a full inspection of the tires, brakes, and engine.
  3. do a quick check of the headlights and high beams.

Answer: A, do a full inspection that checks every light and reflector.. Rest keeps you alert, and a full inspection finds problems before dark. At night, other drivers see your truck by its lights and reflectors, so check and clean every one. (CDL manual 2.11)

At night, to see the road outside your cab, keep your dash lights:

  1. turned up high, so you can read the gauges at a glance.
  2. set at the same level you use in the daytime.
  3. turned down low, but bright enough to read the gauges.

Answer: C, turned down low, but bright enough to read the gauges.. A bright cab makes it harder for your eyes to see outside. Keep the cab light off and dim the gauge lights as far as you can while still reading them. (CDL manual 2.11)

12 Extreme driving conditions

When you drive on an icy road, your truck's retarder should be:

  1. turned to a low setting.
  2. turned to its full setting.
  3. turned off.

Answer: C, turned off.. A retarder slows only the drive wheels. On ice, that can make them lose grip and skid. Keep it off on any wet, icy or snowy road. (CDL manual 2.3.4)

In freezing weather, each of these keeps your windshield washer working EXCEPT:

  1. filling the reservoir with washer antifreeze.
  2. checking that the washer sprays onto the glass.
  3. filling the reservoir with plain water.

Answer: C, filling the reservoir with plain water.. Plain water freezes in the reservoir and lines, so the washer stops working just when road spray covers your windshield. Use washer fluid with antifreeze in it. (CDL manual 2.13)

13 Hazard perceptions

You approach a work zone on the shoulder, but heavy traffic blocks a lane change. You should:

  1. slow down, then pass with extra care.
  2. hold your speed to keep traffic moving.
  3. stop in your lane until traffic clears.

Answer: A, slow down, then pass with extra care.. The best move is a lane away from the work zone. If traffic makes that unsafe, slow down and pass with extra care (CDL manual 2.8).

Near a railroad crossing, the speed you choose should depend mainly on:

  1. the speed limit posted for the road.
  2. how many tracks the crossing has.
  3. how far along the tracks you can see.

Answer: C, how far along the tracks you can see.. Your speed must let you stop before the tracks if a train appears. When trees or buildings block your view, you see trains later, so you must go slower. (CDL manual 2.15.3)

14 Emergency maneuvers

Your truck is stuck on a crossing, and you are calling for help. What detail best pinpoints the crossing?

  1. The crossing's DOT number, posted at the crossing
  2. Your carrier's USDOT number, shown on the cab door
  3. Your truck's license plate and trailer number

Answer: A, The crossing's DOT number, posted at the crossing. Each crossing can have its own DOT number posted on it. Giving that number tells the railroad exactly which crossing is blocked, so it can warn trains fast (CDL manual 2.15).

Your truck thumped hard, and you pulled over, but now it handles fine. Before going on, you should:

  1. look at the two front tires, since they control steering.
  2. walk around the truck and look at every tire.
  3. drive on, since normal handling means the tires are fine.

Answer: B, walk around the truck and look at every tire.. A failed dual tire may not change how the truck feels, because the tire beside it still carries the load. Walking around and looking at each tire is the sure way to find it. (CDL manual 2.17)

15 Skid control and recovery

Your truck has a retarder. Why should you turn it off on a wet or icy road?

  1. Water can get inside it, causing it to fail.
  2. It can make the drive wheels skid, since they have poor grip.
  3. It can lock the front wheels, so you cannot steer.

Answer: B, It can make the drive wheels skid, since they have poor grip.. A retarder slows the drive wheels when you let off the gas. On a slick road, those wheels have little grip, so the retarder can make them skid. (CDL manual 2.3)

Your front wheels start to skid as you steer and brake in a curve. How do you end the skid?

  1. Steer harder and add power so the tires bite.
  2. Ease off the steering and brakes so the truck slows.
  3. Brake hard and hold the wheel so the truck stops.

Answer: B, Ease off the steering and brakes so the truck slows.. A front-wheel skid ends only when the vehicle loses speed. Stop turning and braking so hard, and slow down as fast as you can without skidding. (CDL manual 2.19.3)

16 Relationship of cargo to vehicle control

Under a bridge formula, axles that are close together may carry:

  1. more weight than axles spaced farther apart
  2. the same weight as axles spaced farther apart
  3. less weight than axles spaced farther apart

Answer: C, less weight than axles spaced farther apart. Axles that sit close together put their weight on a short stretch of road or bridge. So a bridge formula gives them a lower weight limit. (CDL manual 3.2.2)

Poor weight balance in a truck is a problem mainly because it can:

  1. push the total weight over the legal limit.
  2. make the engine burn more fuel.
  3. make the truck unsafe to handle.

Answer: C, make the truck unsafe to handle.. Where the weight sits affects steering, traction and rollover risk. A badly balanced load can make the truck hard or unsafe to control. (CDL manual 3.2.4)

17 Vehicle inspections

Your truck has power steering. You find fluid leaking from a hose near the pump. You should:

  1. report it and have it repaired before driving.
  2. add fluid to the reservoir and start your trip.
  3. start your trip and watch for heavy steering.

Answer: A, report it and have it repaired before driving.. Federal rules say a power steering system must not leak. On power steering, check the hoses, the pump and the fluid level, and look for leaks. A leak is a defect, so get it fixed before you drive. (49 CFR 393.209(e))

Your flatbed truck carries a secured load. You stop for a 30-minute meal. Before you drive on, you should:

  1. check the load and its tie-downs again.
  2. check the load at your next fuel stop.
  3. wait to check the load until the 150-mile point.

Answer: A, check the load and its tie-downs again.. A break changes your duty status, and the rule calls for a cargo check every time that happens. Check the load and tie-downs after each break, before you drive on. (49 CFR 392.9)

18 Hazardous materials

You hold a hazmat endorsement and are convicted of a disqualifying crime. You must give up the endorsement to your licensing state within:

  1. 24 hours.
  2. 30 days.
  3. 2 business days.

Answer: A, 24 hours.. A hazmat driver who is convicted of a disqualifying crime must tell the state that issued the CDL and hand back the endorsement within 24 hours. The same deadline applies to an indictment. (CDL manual 1.4)

Where should hazmat shipping papers be when you are out of the vehicle?

  1. In the glove compartment
  2. In your pocket, with you
  3. On the driver's seat

Answer: C, On the driver's seat. When you leave the cab, put the papers on the driver's seat or in the holder on the driver's door. Police and firefighters know to look there after a crash. (49 CFR 177.817(e))

19 Mountain driving

With the transmission in a low gear, engine braking is strongest when the engine is turning:

  1. near its governed rpm.
  2. near its idle rpm.
  3. None of the above.

Answer: A, near its governed rpm.. Governed rpm is the highest engine speed the governor allows. Engine braking holds the truck back hardest near that rpm in a low gear. At low rpm, it slows you much less. (CDL manual 2.6)

On a long, steep downgrade, with no brakes and no low gear holding it back, your truck will:

  1. hold a steady speed at idle.
  2. speed up as gravity pulls it downhill.
  3. slow down once the throttle is closed.

Answer: B, speed up as gravity pulls it downhill.. Going downhill, gravity keeps pulling the heavy truck forward, so its speed keeps rising. A low gear and correct braking are needed to hold it back. (CDL manual 2.16)

20 Fatigue and awareness

You are driving in crowded traffic, and many drivers are on tight schedules. In these conditions, drivers tend to become:

  1. more willing to let other cars merge.
  2. quicker to get angry at one another.
  3. calmer, because no one can go faster.

Answer: B, quicker to get angry at one another.. Packed roads leave little room for mistakes, and tight schedules add pressure. Drivers then grow suspicious and hostile and take other drivers' errors personally. Expect more anger and stay calm yourself. (CDL manual 2.10)

On which road is a driver most likely to grow drowsy?

  1. A long, dark, rural road with little traffic
  2. A busy city street with many traffic lights
  3. A winding mountain road with steep grades

Answer: A, A long, dark, rural road with little traffic. Long, dark, dull roads give your mind little to do, so sleepiness creeps in. Driving alone or after crossing time zones adds to the risk. (CDL manual 2.11)