CDL Prep HeroRead the explanation after every answer. No account needed.
A wheel is about to lock during hard braking. What does ABS do?
What the General Knowledge test covers
The questions come from Section 2 of your state's CDL manual, called Driving Safely. That section is long, but most questions come from a handful of topics: the vehicle inspection, managing speed and space, seeing hazards, driving at night and in bad weather, mountain driving, emergencies, and securing cargo.
Most states give about 50 questions, and you need 80% to pass. That's the federal minimum for every CDL knowledge test.
The numbers worth memorizing
A lot of General Knowledge questions test specific numbers. Following distance is one second for every 10 feet of vehicle length at speeds under 40 mph, plus one more second above 40 mph. Look 12 to 15 seconds ahead. Put out warning devices within 10 minutes of stopping on the road or shoulder.
Cargo securement is not one universal tiedown-count rule. Required securement depends on the cargo, its size and weight, blocking, and the securement system. Study your current manual and the applicable cargo-securement rules with an instructor.
How to study for it
Read Section 2 of the manual once, then switch to practice questions. When you miss one, read the explanation and go back to that part of the manual. Keep going until you're scoring well above 80%, so a few unfamiliar questions on test day won't sink you.
Common questions
How many questions are on the CDL General Knowledge test?
It varies by state, but most states give 50 questions. You need to answer at least 80% correctly to pass.
Do I need the General Knowledge test for a Class B CDL?
Yes. Everyone applying for a Class A or Class B CDL takes the General Knowledge test. Air Brakes and Combination Vehicles are added depending on the vehicle you'll drive.
What happens if I fail the CDL permit test?
You can retake it. Waiting periods and retest fees depend on your state, so check with your state's licensing agency.
Questions and explanations
Prefer to read? Review the same 50 practice questions here. These are original study questions, not official exam questions. Our practice questions include explanations to help you return to the relevant official manual material.
A wheel is about to lock during hard braking. What does ABS do?
It lowers and adjusts brake pressure to keep the wheel from locking.
ABS sensors spot the wheel about to lock. The control unit then adjusts brake pressure to give the most braking without a lockup.
Cargo is piled high, or heavy cargo sits on top. What handling risk does that bring?
A greater chance of rollover in a curve or a sudden swerve.
A high center of gravity makes a rollover more likely, especially in a curve or a sudden swerve.
You're picking up an unsealed load. Warehouse staff secured it. What's the best pre-trip action?
Check for overload, balance, and proper securement before you leave.
Your pre-trip cargo duties include checking load, balance, and securement. That is true even when someone else loaded it.
You're picking a parking spot at the end of a stop. Which plan cuts down the next backing move?
Park so you can pull out forward when you can.
This avoids a risky backing move whenever the parking spot allows it.
After a crash, the vehicle can be moved safely. What should you do to help prevent another crash?
Move the vehicle to the side of the road.
When it's safe to move, getting the vehicle to the roadside helps prevent another crash and lets traffic move.
You slept fine, but you feel mentally tired after repetitive work while getting over an illness. Which is right?
Fatigue is still possible, because repetitive work and illness can cause it.
Fatigue can come from repetitive work or illness, not just from lost sleep.
You're using controlled braking with no ABS. The wheels lock, and you need a bigger steering correction. What do you do?
Let off the brakes, make the correction, and reapply as soon as you can while the wheels keep rolling.
Letting off gets the wheels rolling so you can make the bigger correction. Brake again once you have control.
Why does it matter to spot a hazard before it becomes an emergency?
It gives you more time to plan before things change.
Spotting it early keeps your planning time. Seeing the problem only after it changes forces a sudden response.
What is the main purpose of a commercial vehicle inspection?
To find problems that could lead to a crash or breakdown.
Finding defects protects you and other road users. It can prevent a crash or breakdown.
You see no vehicle in the mirrors. You decide there's no traffic anywhere beside or behind you. What's the best take on that?
Mirrors can leave areas unseen, so an empty mirror does not prove there's nothing there.
Mirrors have blind spots, which are areas they can't show.
Traction is poor as you start moving. How should you apply power?
Accelerate very gradually.
Gradual acceleration lowers the chance of spinning the drive wheels and losing control.
Use the handbook teaching rule. What following gap fits a 50-foot vehicle going under 40 mph in normal conditions?
At least 5 seconds.
One second for each 10 feet gives a 50-foot vehicle a five-second gap below 40 mph.
What is one thing ABS gives you during hard braking?
It helps you keep control and steer around something while braking.
By keeping wheels from locking, ABS helps you keep control. You may still be able to steer around something while braking.
What happens when too much weight sits on the steering axle?
Steering can get hard.
Too much weight on the steering axle makes steering hard.
You started with unsealed cargo you can reach. You've driven 45 miles. What's the next step?
Plan to recheck the cargo and securement devices before you pass 50 miles, and adjust as needed.
Unsealed cargo you can reach must be checked again within the first 50 miles. Adjust the securement if needed.
You have to back up. What's the right way to check the path first?
Stop, put it in neutral, set the parking brake, get out safely, and walk the path and clearances.
The truck must be stopped, in neutral, and held by the parking brake. Then you walk the path and check side and overhead clearance.
You stop to help at a crash. Where should you park?
Away from the crash, so emergency vehicles have room near it.
Parking away from the crash keeps space open near the scene for emergency vehicles.
Which sign of fatigue means you should stop and rest?
Missing a familiar exit and not remembering the last few miles.
Missing signs or exits and forgetting recent miles are known warning signs of fatigue.
The manual has one exception that allows a full brake application in an emergency stop. When does it apply?
To a straight truck or combination vehicle with working ABS on every axle.
The exception covers only those vehicles, and only when ABS works on every axle.
In the manual's example, what change turns the situation from a hazard into an emergency?
The car ahead cuts in front of you after braking near the freeway exit.
In the manual's example, the car is a hazard while it may return to the highway. Once it cuts in front of you, it's an emergency.
Which approach best fits inspection awareness while a trip is underway?
Watch gauges and use sight, hearing, smell, and feel for signs of trouble.
During the trip, you watch the gauges and use your senses to catch possible trouble.
You want a mirror that shows more area than a flat mirror. Which statement names the real difference?
A convex mirror shows a wider area than a flat mirror.
The wider field of view is the difference between convex and flat mirrors.
Which sign warns that water may be collecting on the road?
Reflections on the road and tire splashes.
Reflections and splashes are visible signs that standing water may be present.
Use the same teaching rule. What gap fits a 60-foot rig going over 40 mph, before any other adjustment?
At least 7 seconds.
Six seconds comes from the 60-foot length. Going over 40 mph adds one second.
You've recognized a hazard but haven't yet pressed the brake. Which part of the stopping-distance model is this?
Reaction distance.
Reaction distance is the travel after you recognize the hazard and before you apply the brakes.
Which kind of skid is ABS meant to help prevent?
A braking skid caused by braking too hard.
ABS keeps wheels from locking. That helps prevent braking skids and jackknifes.
Weight shifts too far back and the front axle is under-loaded. What can happen?
The steering axle can get too light to steer safely.
A front axle made too light by weight shifting back can make safe steering hard.
A shipper hands you a loaded, sealed trailer. What's the best way to handle loading and weight duties?
Keep the seal on unless approved to break it, check weight limits, and use an accepted carrier method for proper loading.
You can't check a sealed load directly. But weight limits and carrier loading duties still apply. Supervision, a proper-loading note, or approved seal-breaking can cover loading.
Two routes reach the same backing spot. One lets you back toward the driver's side. Which is better?
The driver-side route, because you can see better, even if it takes longer to set up.
Backing toward the driver's side gives you a better view. Extra driving to get that position can be worth it.
It's safe to set out warnings at a crash. Which approach matches the guidance?
Use hazard flashers and set reflective triangles where drivers can see them in time to avoid the crash.
Hazard flashers and visible reflective triangles warn traffic. The test is seeing them in time, not one set distance.
Your eyelids feel heavy and you keep yawning. What's the safe response?
Stop driving at a safe place and sleep.
Heavy eyelids and yawning are warnings. The safe cure for drowsiness is to stop and sleep.
You're braking a combination vehicle with ABS. What check should you keep making?
Watch both the tractor and trailer, and ease off if safe when you need to keep control.
Braking a combination with ABS still means watching both units and adjusting safely to keep control.
A cardboard box on the road looks harmless. What is the real concern?
It may hold something solid or heavy that can cause damage.
The manual warns that light-looking objects can hide damaging contents. They can hurt tires, rims, lines, or dual tires.
Which statement about the after-trip inspection and report is correct?
It happens at the end of duty and can tell the carrier what needs repair.
The timing is the end of the trip, day, or tour of duty. The report helps identify what needs repair.
A vehicle looks small and far away in a convex mirror. What should you understand about that image?
The mirror makes the vehicle look smaller and farther away than it really is.
Convex mirrors change how big and how far away an object looks in the image.
You're near a bridge in cold weather. What change in other vehicles warns that ice may have formed?
Their tires stop throwing spray.
No spray is one sign that water on the road may have turned to ice.
You count from a fixed pavement mark and find your gap is shorter than the rule. The road is also slippery. What's the best response?
Drop back, count again, and allow much more stopping space.
A short count means drop back and count again. Slippery roads call for much more stopping space.
Which statement best describes the stopping-distance model for a vehicle with air brakes?
It has three general parts. Air brakes can add a lag before the brakes work.
The three-part model is a general idea. The manual separately lists air-brake lag as an added delay for air brakes.
What does ABS not make up for?
Bad brakes or poor brake upkeep.
ABS does not make up for bad brakes or poor brake upkeep.
What happens when too little weight sits on the drive axles?
Poor traction, so the drive wheels can spin easily.
Too little weight on the drive axles can cause poor traction and easy wheel spin.
Crates can slide sideways across a flat deck. Which blocking plan stops that movement?
Fit blocking snug against the sides of the crates and fix it to the deck.
Side blocking that fits snug and is fixed to the deck directly stops sideways sliding.
Where should your helper stand for a backing move?
Near the rear, in a spot you can see before and during backing.
That spot lets the helper watch the rear while staying in your view.
You're at a crash. No fire, no other reason to get out, and you're safe inside with a working phone. What do you do first?
Call for help before you get out.
When staying inside is safe and you have a phone, call for help before you get out.
Which pair correctly labels one inside distraction and one outside distraction?
Adjusting a control is inside; watching a crash scene is outside.
Adjusting a control happens inside the truck. A crash scene is an outside event that can pull your attention.
There's an obstacle ahead and not enough room to stop. When may steering around it be the safer choice?
When a safe path around the obstacle is open.
Not having room to stop supports steering only when the open path is safe.
Why is a blocked view a possible hazard?
A partly hidden vehicle may back out or pull into your lane without its driver seeing you.
The Blocked Vision section says a vehicle partly hidden by an intersection or alley may back out or enter your lane when its driver can't see you.
Which tread-depth pair matches the inspection limits?
At least 4/32 inch in every major groove on front tires, and 2/32 inch on other tires.
Front tires need at least 4/32 inch in every major groove. Other tires need at least 2/32 inch.
You keep staring at a mirror to gather more information. What's the better way to use your attention?
Keep the check quick, and shift your eyes back and forth between the mirror and the road ahead.
Staring at a mirror can leave you unaware of what's happening ahead for some distance.
Which approach best fits choosing your speed when road conditions change?
Adjust speed for traction, curves, visibility, traffic, and hills.
Safe speed changes with the road, your view, traffic, and terrain. It does not stay fixed.
A car starts tailgating your heavily loaded truck as it slows on an uphill grade. What should you do first?
Increase the space ahead of your truck.
More space ahead cuts the need for sudden changes. It can also make it easier for the car to get around you.
Study sources and limitations
Editorial attribution: Evergreen Comply, LLC Editorial Staff. Our practice questions include explanations to help you return to the relevant official manual material.
Use your current state manual and a qualified instructor for licensing requirements and hands-on procedures. This practice set does not replace required training or certify readiness to drive.
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Source links checked September 25, 2026.
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