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California CDL General Knowledge Test study materials
California CDL General Knowledge Test study resources

California CDL General Knowledge Test practice questions

One question at a time. Build your California CDL General Knowledge Test understanding.

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Question 1Driving Safely

Why should a CMV driver wear a safety belt?

  1. It allows the driver to exceed the posted speed limit by 5 mph.
  2. It keeps you behind the wheel and in control. Correct answer.
  3. It replaces the need for a pre-trip inspection of the cab.
  4. It is required only when the vehicle carries hazardous materials.

Explanation

A safety belt holds you in the seat so you stay behind the wheel and can control the vehicle during a crash or sudden stop. It also keeps you from being thrown from the cab, which is the most dangerous outcome in a truck crash.

Question 2Driving Safely

What happens when a vehicle hydroplanes?

  1. The tires are overinflated and bounce off the pavement.
  2. The brakes get hot and fade on a long downgrade.
  3. The engine loses power because of moisture in the fuel.
  4. Tires ride on water and lose road contact. Correct answer.

Explanation

Hydroplaning occurs when water builds up under the tires faster than the tread can push it away, so the tires ride on a film of water instead of the road. Steering and braking become ineffective until the tires regain contact with the pavement.

Question 3Driving Safely

What should you check before driving a CMV across railroad tracks?

  1. Rely on the crossing gate to stop all other traffic.
  2. Make sure there is room to clear the tracks completely. Correct answer.
  3. Stop on the tracks briefly to look both ways.
  4. Shift to a higher gear while the vehicle is on the tracks.

Explanation

You should never enter a crossing unless you can clear the tracks completely on the far side. A long vehicle can be struck if traffic backs up and leaves the trailer sitting on the rails.

Question 4Driving Safely

You must back a CMV and no helper is available. What should you do?

  1. Get out and check the area behind the unit first. Correct answer.
  2. Sound the horn and back without looking behind the unit.
  3. Use only the right-side mirror while backing.
  4. Back quickly to spend as little time as possible in the blind spot.

Explanation

Without a helper, you should walk around and inspect the area behind the vehicle before backing, because large blind spots can hide people, vehicles, or objects. Back slowly and recheck as you go, stopping if you are unsure.

Question 5Driving Safely

Which statement about texting while driving a CMV is correct?

  1. It is permitted whenever you are stopped at a red light.
  2. It is allowed when traffic is light and no police are nearby.
  3. It is prohibited and takes your attention off the road. Correct answer.
  4. It is safe if you hold the phone with one hand.

Explanation

Texting is prohibited for CMV drivers, and it combines all three types of distraction: your eyes, hands, and mind leave the driving task. Even a brief glance at a phone can cover a long distance at highway speed.

Question 6Driving Safely

At night, when should you dim your headlights for an oncoming vehicle?

  1. Within 500 feet of the oncoming vehicle. Correct answer.
  2. Only after the other driver dims his or her headlights first.
  3. Within 100 feet of the oncoming vehicle.
  4. Never, as long as the road has no street lights.

Explanation

You must switch to low beams when an oncoming vehicle is within 500 feet, and within 300 feet when following another vehicle. Dimming prevents glare that can temporarily blind the other driver.

Question 7Driving Safely

How should you drive through a highway work zone?

  1. Maintain your speed so you do not disrupt the flow of traffic.
  2. Slow down and obey the flagger and posted speed limit. Correct answer.
  3. Follow the vehicle ahead closely so you do not get separated.
  4. Use the shoulder to pass slow-moving construction equipment.

Explanation

Work zones often have narrowed lanes, workers near the roadway, and sudden stops, so you must reduce speed and follow the flagger and posted limits. Fines for moving violations are typically higher in work zones.

Question 8Driving Safely

What should you do if you become sleepy while driving?

  1. Stop at a safe place and rest until you are alert. Correct answer.
  2. Speed up so you reach your destination sooner.
  3. Drink coffee and keep driving to the next town.
  4. Open the window and turn up the radio to stay awake.

Explanation

Fatigue cannot be overcome by fresh air, music, or caffeine; the only real cure is sleep. Pull over in a safe place and rest, or take a nap, before continuing.

Question 9Driving Safely

Which items make up a CMV's total stopping distance?

  1. Perception, reaction, brake lag, and braking distance. Correct answer.
  2. The distance covered during the pre-trip inspection.
  3. Only the distance traveled while the brakes are applied.
  4. The length of the vehicle plus any load overhang.

Explanation

Total stopping distance starts when you see a hazard and adds perception distance, reaction distance, brake lag, and the actual braking distance. At highway speed, the distance before the brakes even engage is substantial.

Question 10Driving Safely

A 60-foot combination vehicle is traveling at 50 mph. What is the minimum following distance you should keep?

  1. 7 seconds Correct answer.
  2. 4 seconds
  3. 10 seconds
  4. 5 seconds

Explanation

Use one second for each 10 feet of vehicle length, which gives 6 seconds for a 60-foot vehicle below 40 mph. Above 40 mph, add one more second, so at 50 mph you need at least 7 seconds.

Question 11Driving Safely

If your rear wheels begin to skid, how should you steer?

  1. Turn the wheel in the direction you want the front to go. Correct answer.
  2. Shift to neutral and coast until the skid stops.
  3. Accelerate to pull the vehicle out of the skid.
  4. Apply the brakes hard and hold the steering wheel straight.

Explanation

To correct a rear-wheel skid, stop braking or accelerating to let the tires regain traction and steer in the direction you want the front of the vehicle to go. Steering opposite the skid will make the vehicle spin.

Question 12Driving Safely

What is an escape ramp on a steep downgrade used for?

  1. Parking overnight when rest areas are full.
  2. Turning around when you miss an exit.
  3. Stopping a vehicle that has lost its brakes. Correct answer.
  4. Checking and adjusting cargo securement.

Explanation

Escape ramps are built at the bottom of long grades to catch vehicles whose brakes have failed or faded. If you lose braking ability, steer for the ramp and do not try to continue down the grade.

Question 13Driving Safely

Before starting down a long, steep downgrade, what should you do?

  1. Put the transmission in neutral to save fuel.
  2. Rely on the brakes and keep the clutch pushed in.
  3. Select a gear that holds your speed without heavy braking. Correct answer.
  4. Speed up at the top to carry momentum down the grade.

Explanation

Choose a gear before the grade begins that lets the engine hold your speed with only light brake use. Riding the brakes down a long grade overheats them and causes brake fade or complete loss of braking.

Question 14Driving Safely

How should you drive when visibility is reduced by fog?

  1. Use high beams so you can see farther through the fog.
  2. Stop in your lane and turn on your flashers.
  3. Slow down and use low-beam headlights. Correct answer.
  4. Follow the tail lights of the vehicle ahead closely.

Explanation

High beams reflect off fog and make visibility worse, so use low beams and reduce speed. If you must stop, leave the roadway entirely rather than stopping in a travel lane.

Question 15Driving Safely

In hot weather, how should you check your tires during a trip?

  1. Once at the end of the trip, when the tires have cooled.
  2. Only during the pre-trip inspection, before the trip starts.
  3. After the first 50 miles, then every 150 miles or 2 hours. Correct answer.
  4. Only if a tire looks flat or sounds low.

Explanation

Heat builds up in tires as they run, and a soft or underinflated tire can overheat and fail. The standard practice is to check after the first 50 miles and then every 150 miles or 2 hours in hot weather.

Question 16Driving Safely

What should you do after driving through deep water?

  1. Pump the brakes hard while the vehicle is stopped.
  2. Test them gently at low speed to dry them out. Correct answer.
  3. Set the parking brake until the brakes dry out.
  4. Drive at highway speed right away to blow them dry.

Explanation

Water can make the brakes weak or grabby, so you should test them gently at low speed while applying light pressure to heat and dry the linings. If braking is still poor after that, stop and check the brakes before continuing.

Question 17Driving Safely

What should you confirm before driving under a low bridge or overpass?

  1. The clearance only if the load looks unusually tall.
  2. That you can pass under it before the light changes.
  3. Your total height, including the load. Correct answer.
  4. That the posted clearance applies to trucks.

Explanation

You must know the total height of the vehicle and load and compare it with the posted clearance before entering. Clearance signs are posted for the lowest point, and striking a bridge can cause serious injury and structural damage.

Question 18Driving Safely

What should you do if a front tire blows out at highway speed?

  1. Hold the wheel firmly and slow down gradually. Correct answer.
  2. Accelerate to stabilize the vehicle.
  3. Jerk the steering wheel toward the shoulder.
  4. Brake hard right away to stop as quickly as possible.

Explanation

A front tire failure pulls the steering, so grip the wheel firmly, keep the vehicle straight, and slow gradually before easing onto the shoulder. Hard braking or sharp steering at speed can cause a loss of control or a rollover.

Question 19Driving Safely

After passing another vehicle, when should you return to the right lane?

  1. Whenever the driver you passed flashes the headlights.
  2. Only after you reach the next exit or interchange.
  3. As soon as your front bumper clears the other vehicle.
  4. When you can see the passed vehicle in your right mirror. Correct answer.

Explanation

You need enough room so the passed vehicle is visible in your right mirror before you move back over. Returning too soon can clip the other vehicle or force it onto the shoulder.

Question 20Driving Safely

How should a large CMV make a right turn?

  1. Start from the right lane and swing wide as needed. Correct answer.
  2. Start the turn from the left lane to make extra room.
  3. Turn sharply so the trailer stays inside the right lane.
  4. Ignore the rear wheels because they follow the front wheels.

Explanation

Begin the turn from the right lane and swing wide to the left as necessary so the rear wheels do not climb the curb or hit a pole. Check the right mirror throughout the turn to track the trailer.

Question 21Driving Safely

At 55 mph, about how much extra distance does air brake lag add before the brakes begin to work?

  1. About 4 feet
  2. There is no lag with air brakes
  3. About 32 feet Correct answer.
  4. About 100 feet

Explanation

Air takes time to travel through the lines and apply the brakes, which adds roughly 32 feet at 55 mph on dry pavement. Hydraulic brakes do not have this lag, so the difference matters when judging stopping distance.

Question 22Driving Safely

What should you do if a fire starts in your cargo area?

  1. Use water on the fire no matter what the cargo is.
  2. Stop, get out, call for help, and keep the cargo area closed. Correct answer.
  3. Open the cargo doors wide so smoke and heat escape quickly.
  4. Keep driving to the nearest fire station.

Explanation

Stop, get yourself and others away, and call for help. Keeping the cargo compartment closed limits the oxygen feeding the fire and protects you from toxic smoke and explosions.

Question 23Driving Safely

When a long CMV makes a turn, what do the rear wheels do?

  1. They follow a shorter path, so the rear may hit the curb. Correct answer.
  2. They track wider than the front wheels, but only when loaded.
  3. They swing wider than the front wheels and clear the curb.
  4. They follow exactly the same path as the front wheels.

Explanation

This is called off-tracking: the rear wheels cut inside the path of the front wheels. The longer the vehicle, the more the rear wheels cut the corner, so you must allow extra room when turning.

Question 24Driving Safely

If you double your speed, what happens to your braking distance?

  1. It stays about the same.
  2. It becomes about four times as long. Correct answer.
  3. It becomes half as long.
  4. It becomes twice as long.

Explanation

Braking distance increases with the square of speed, so doubling speed multiplies braking distance by about four. Total stopping distance grows even more because perception and reaction distance also increase with speed.

Question 25Driving Safely

Why should a retarder be turned off on a slippery road?

  1. It overheats the steering axle and damages the tires.
  2. It uses too much fuel on wet pavement.
  3. It can make the drive wheels skid. Correct answer.
  4. It is designed only for use on flat ground.

Explanation

A retarder applies resistance at the drive wheels, and on a slippery surface that can break traction and cause a skid. Turn it off when the road is wet, icy, or snow-covered and use engine braking and light brake pressure instead.

Question 26Driving Safely

When is a CMV driver required to wear a seat belt?

  1. Whenever driving on a public road Correct answer.
  2. Only when passengers are aboard
  3. Only during bad weather
  4. Only on interstate highways

Explanation

Seat belts are required any time a CMV is operated on a public road. They keep the driver behind the wheel and help prevent ejection in a crash.

Question 27Driving Safely

Why should you check your mirrors regularly while driving a CMV?

  1. To estimate the vehicle's fuel mileage
  2. To decide the best moment to change gears
  3. To verify that the cargo remains tied down
  4. To track traffic and lane position Correct answer.

Explanation

Regular mirror checks keep you aware of traffic around the vehicle and help you maintain proper lane position. Mirrors should be checked often and before any lane change or maneuver.

Question 28Driving Safely

When should you activate your turn signal before a lane change?

  1. Early enough to give other drivers warning Correct answer.
  2. At the moment you check your mirror
  3. After you begin moving into the new lane
  4. Only if another driver is nearby

Explanation

Signal early enough for other drivers to see your intention and react. A signal that starts after the maneuver has begun does not give others time to adjust.

Question 29Driving Safely

What is a space cushion in driving?

  1. The open space you keep around your vehicle Correct answer.
  2. The distance between your tires and the curb
  3. The padding inside the cab's seats
  4. The gap between your cargo and the trailer wall

Explanation

A space cushion is the open area you maintain around your vehicle so you have room to stop or steer if traffic changes suddenly. It includes following distance and space to the sides.

Question 30Driving Safely

How far ahead should you look while driving at highway speed?

  1. Only as far as your headlights reach
  2. About 2 to 3 seconds ahead
  3. About 30 to 40 seconds ahead
  4. About 12 to 15 seconds ahead Correct answer.

Explanation

At highway speed you should scan about 12 to 15 seconds ahead, which is roughly a quarter mile at 55 mph. Looking farther lets you spot hazards and plan lane and speed changes.

Question 31Driving Safely

What should you do if your vehicle begins to hydroplane?

  1. Turn sharply toward the shoulder to escape
  2. Accelerate to push through the standing water
  3. Ease off the accelerator and steer straight Correct answer.
  4. Brake firmly to regain traction quickly

Explanation

Hydroplaning occurs when water lifts the tires off the road, so steering and braking become ineffective. Ease off the accelerator, keep the wheel straight, and avoid hard braking until traction returns.

Question 32Driving Safely

How should you respond when a driver is tailgating your CMV?

  1. Brake sharply to warn the driver behind
  2. Move onto the shoulder and stop at once
  3. Speed up to increase the gap behind you
  4. Leave extra room ahead and slow gently Correct answer.

Explanation

A tailgater needs more time to react, so create extra room ahead and slow gradually rather than braking suddenly. If possible, let the driver pass.

Question 33Driving Safely

What should you do before backing a large CMV when a helper is available?

  1. Sound the horn and back without checking
  2. Rely only on the mirrors and skip the helper
  3. Back quickly to minimize the time
  4. Use the helper and check your mirrors Correct answer.

Explanation

A helper can guide you, but the driver remains responsible for checking the area behind the vehicle. Use the helper's signals and verify with mirrors before backing.

Question 34Driving Safely

What is the safest way to enter a curve in a CMV?

  1. Slow before the curve, then accelerate gently Correct answer.
  2. Shift to neutral and coast through the entire curve
  3. Maintain highway speed and steer sharply
  4. Brake hard while inside the curve

Explanation

Speed should be reduced before the curve because braking in a curve can cause a skid or rollover. After entering, accelerate gently to maintain control.

Question 35Driving Safely

If your vehicle stalls or becomes stuck on a railroad crossing, what should you do first?

  1. Place reflective triangles behind the vehicle
  2. Try to restart the engine repeatedly
  3. Get everyone out and leave the tracks Correct answer.
  4. Stay in the cab and call your dispatcher

Explanation

If a vehicle is stuck on a crossing, occupants should get out immediately and move away from the tracks. Then call 911 and the railroad's emergency number.

Question 36Driving Safely

What is the first action you should take if your service brakes fail while driving?

  1. Turn off the ignition switch immediately
  2. Pump the accelerator pedal to build pressure
  3. Shift the transmission to neutral and coast
  4. Downshift and use the emergency brake gently Correct answer.

Explanation

When service brakes fail, downshift to use engine braking and apply the emergency or parking brake gradually. Turning off the engine can lock the steering, and pumping the accelerator does not restore brake pressure.

Question 37Driving Safely

If a fire starts in your engine compartment while driving, what should you do?

  1. Continue driving to the nearest service station
  2. Stop, shut off the engine, and evacuate Correct answer.
  3. Open the hood fully and spray water
  4. Shift to neutral and let the engine race

Explanation

Stop, shut off the engine to cut off fuel, and get everyone out of the vehicle. Call for help, and use an extinguisher only if it is safe and you can avoid fully opening the hood.

Question 38Driving Safely

What does it mean to overdrive your headlights at night?

  1. Driving with a burned-out headlight
  2. Driving beyond the reach of your headlights Correct answer.
  3. Keeping your dashboard lights too bright
  4. Using high beams when no traffic is present

Explanation

Overdriving headlights means your speed is too fast for the distance you can see and stop. At night, you must be able to stop within the lighted area ahead.

Question 39Driving Safely

While driving a CMV, when may you use a hand-held mobile phone?

  1. While stopped at a red light
  2. Only on rural roads
  3. Never, except in an emergency Correct answer.
  4. Only when the call is work-related

Explanation

Federal rules prohibit hand-held mobile phone use while driving a CMV, with a limited exception for emergencies. Waiting at a light or making a work call does not create an exception.

Question 40Driving Safely

What should you do when an emergency vehicle with flashing lights approaches from behind?

  1. Turn on your high beams to signal
  2. Stop immediately in your current traffic lane
  3. Pull to the right and stop clear of traffic Correct answer.
  4. Speed up to reach the next exit

Explanation

When an emergency vehicle approaches with lights or siren, pull to the right and stop clear of the roadway. Remain stopped until it passes.

Question 41Transporting Cargo Safely

After you load cargo and begin driving, when must you first stop to inspect the load and the securement devices?

  1. After about 150 miles of driving
  2. Only after you reach the destination
  3. Only if the cargo starts making noise
  4. After about 50 miles of driving Correct answer.

Explanation

Cargo and its tiedowns must be inspected within the first 50 miles after loading, then again every 150 miles or 3 hours, whichever comes first. Loads settle and straps loosen as the vehicle moves, so the first check comes early.

Question 42Transporting Cargo Safely

The maximum total weight a vehicle may safely carry, including the vehicle itself, fuel, and cargo, is called the:

  1. curb weight
  2. payload capacity
  3. axle weight rating
  4. gross vehicle weight rating Correct answer.

Explanation

The gross vehicle weight rating (GVWR) is the manufacturer's maximum safe total weight for the whole vehicle. Exceeding the GVWR, or the rating of any axle, overstresses tires, brakes, and suspension.

Question 43Transporting Cargo Safely

What is the strong barrier at the front of the cargo space that must be able to hold the cargo in place during a sudden stop?

  1. Mud flap
  2. Side rail
  3. Dock bumper
  4. Header board Correct answer.

Explanation

The front end structure of a cargo space is called a header board or front-end structure. It must be strong enough to stop the cargo from sliding forward into the cab during hard braking.

Question 44Transporting Cargo Safely

What is the minimum number of tiedowns required for a single article of cargo that is 20 feet long and weighs 900 pounds?

  1. Three tiedowns Correct answer.
  2. Two tiedowns
  3. One tiedown
  4. Four tiedowns

Explanation

For an article longer than 10 feet, use one tiedown for each 10 feet of length plus one additional tiedown. A 20-foot article therefore needs at least three tiedowns.

Question 45Transporting Cargo Safely

The combined working load limit of all tiedowns used on an article of cargo must be at least what fraction of the weight of the article?

  1. Twice the cargo weight
  2. One-half of the cargo weight Correct answer.
  3. The full cargo weight
  4. One-quarter of the cargo weight

Explanation

The aggregate working load limit of all tiedowns on an article must be at least 50 percent of the article's weight. Many loads need well above this minimum to stay put.

Question 46Transporting Cargo Safely

When loading a vehicle, where should the heaviest items be placed?

  1. On the floor, as low as possible Correct answer.
  2. Piled against the rear doors
  3. Wedged behind the header board
  4. As high as possible, directly over the axles

Explanation

Keeping heavy items low and near the center of the vehicle lowers the overall center of gravity. A low center of gravity reduces rollover risk and helps the vehicle handle predictably.

Question 47Transporting Cargo Safely

Which of these is a legal requirement for a loaded commercial vehicle?

  1. The cargo must not hide lights, reflectors, or the license plate Correct answer.
  2. The cargo must be loaded by the shipper
  3. The cargo must be covered with a tarp at all times
  4. The cargo must be held with chains rather than straps

Explanation

Required lights, reflectors, and the license plate must stay visible so other drivers and officers can see them. A tarp, chains, or a shipper loading the freight are not universal legal requirements.

Question 48Transporting Cargo Safely

While driving, you notice that the steering and braking suddenly feel different from when you started. What is the most likely explanation?

  1. The trailer lights are turning on by themselves
  2. The engine temperature has risen
  3. The cargo has shifted Correct answer.
  4. The mirrors need to be adjusted

Explanation

A load can move even if it was secure when you left. A change in steering or braking feel is a warning to stop in a safe place and inspect the cargo and tiedowns.

Question 49Transporting Cargo Safely

You pick up a trailer loaded with freight that carries a seal. What should you do with the seal?

  1. Break the seal and then attach one of your own seals
  2. Leave it on unless you must break it, and note the reason on the shipping papers Correct answer.
  3. Break the seal immediately so you can count the cargo
  4. Remove the seal and hand it to the receiver at delivery

Explanation

A seal shows the load has not been opened in transit, so it normally stays intact. If you must break it, record the reason on the shipping papers so the receiver knows why the seal is missing.

Question 50Transporting Cargo Safely

While driving, you discover that part of your load of hazardous material has spilled onto the roadway. What should you do first?

  1. Continue to the next town to find a telephone
  2. Wash the material off the road with water
  3. Keep people away and notify the proper authorities Correct answer.
  4. Put the spilled material back on the truck by hand

Explanation

Stop, keep others away from the spill, and notify emergency responders and your carrier. Only people trained and equipped to handle hazardous materials should deal with a release.