General Knowledge CDL Practice Test
The General Knowledge exam is the foundation test required for every Commercial Driver's License applicant in every U.S. state. It covers driver qualification, vehicle inspection, basic control, communicating, controlling speed, managing space, seeing hazards, distracted and aggressive driving, night and adverse-weather driving, railroad-highway crossings, accident procedures, fires, alcohol and drug rules, and the hazardous-materials awareness section that every driver must know — even those without an H endorsement.
What's on the General Knowledge exam
Most state DMVs administer 50 General Knowledge questions and require 80% (40 correct) to pass. Questions are pulled from a much larger pool, so two applicants taking the test on the same day will see different mixes. The questions on this site are drawn from the AAMVA CDL Manual chapters that every state's exam is built from.
Topics covered
- Commercial driver qualifications and disqualifications
- Vehicle inspection: pre-trip, en-route, and post-trip
- Basic vehicle control: starting, stopping, backing, turning
- Shifting gears and engine RPM
- Communicating: signaling, horn, headlights, four-ways
- Controlling speed: stopping distance, speed and curves, downgrades
- Managing space: ahead, behind, sides, overhead, below
- Seeing hazards and the hazard-perception process
- Distracted, aggressive, drowsy, and impaired driving
- Night driving and adverse weather (rain, snow, ice, fog, hot pavement)
- Railroad-highway grade crossings
- Mountain driving and runaway escape ramps
- Driving emergencies, skid control and recovery
- Accident procedures, fires, and reporting
- Hazardous materials awareness for all drivers
- Alcohol, drugs, and the .04 BAC commercial standard
Who needs this endorsement
Every CDL applicant must pass General Knowledge. There are no exemptions. Pass this test before attempting any endorsement-specific exam.
All 97 General Knowledge Practice Questions
Click any answer to reveal the correct one and the explanation. Take a state-specific 20-question randomized round on any of the state pages.
You are about to drive a vehicle that you have not driven before. What should you do?
Correct. Federal regulations require the driver to be satisfied that the vehicle is in safe operating condition before driving. The previous driver's inspection does not relieve you of that responsibility.
The most important reason for doing a vehicle inspection is to:
Correct. A pre-trip inspection is meant to find problems that could cause a crash or breakdown. Compliance is a side effect, not the purpose.
Which of the following is NOT part of the seven-step pre-trip inspection method?
Correct. The radio is not part of the safety inspection. The seven-step method covers approach, engine compartment, in-cab checks, lights, walk-around, signal lights, and brake checks.
How many red reflective triangles must you carry in your commercial vehicle for emergency warning?
Correct. You must carry three red reflective triangles, six fusees, or three liquid-burning flares for emergency warning use.
When should you place reflective triangles on a divided highway after stopping due to a breakdown?
Correct. On a divided highway with traffic from one direction, place triangles 10, 100, and 200 feet behind the vehicle, on the shoulder or in the lane you stopped in.
Which of these is a sign of tire failure?
Correct. Vibration, a loud bang from a blowout, and pulling to one side are all classic signs of tire failure.
When the engine is running in the cab inspection, you should check:
Correct. After starting, watch the gauges to be sure all systems are operating normally before you drive.
How often must drivers inspect their cargo and securing devices?
Correct. Federal rule: inspect within the first 50 miles, then every 150 miles or 3 hours of driving, whichever comes first, plus every change of duty status.
On a 6-tire single vehicle, the maximum allowable air loss rate (engine off, brakes released) is:
Correct. For a single vehicle, no more than 2 psi per minute leakage with the engine off and brakes released. Combinations are limited to 3 psi/min.
You are driving a 40-foot vehicle at 35 mph. The minimum following distance you should maintain is:
Correct. The rule of thumb: 1 second per 10 feet of vehicle length below 40 mph. A 40-foot vehicle therefore needs 4 seconds of following distance.
You are driving a 60-foot tractor-trailer at 55 mph. The minimum following distance you should maintain is:
Correct. Above 40 mph, add one extra second to the per-10-foot rule. A 60-foot vehicle = 6 seconds + 1 = 7 seconds at 55 mph.
Which of these is true about driving in fog?
Correct. In fog, high beams reflect off water particles and impair vision. Use low beams. Many drivers also use four-way flashers when moving slowly to alert traffic.
Hydroplaning is most likely to occur when:
Correct. Hydroplaning occurs when a film of water comes between the tires and the road, causing the tires to lose contact with the pavement. Higher speeds, worn tires, and standing water increase the risk.
If your vehicle hydroplanes, what should you do?
Correct. Release the accelerator and push in the clutch. Do not brake or steer hard until the tires regain contact.
What is the minimum tread depth required for the front (steering) tires of a commercial vehicle?
Correct. Steer-axle tires must have at least 4/32-inch tread depth in every major groove. Other tires require at least 2/32 inch.
The blood-alcohol concentration (BAC) at or above which a CDL driver is considered to be driving under the influence in a commercial motor vehicle is:
Correct. The federal BAC limit for CDL drivers operating a commercial vehicle is .04 — half the .08 limit for non-commercial drivers in most states.
What is the only effective way to remove alcohol from the body?
Correct. Only time eliminates alcohol from the body — at roughly one drink per hour. Coffee, food, and showers do not speed up the process.
You are driving on a two-lane road. An oncoming driver drifts into your lane. You should:
Correct. When an oncoming driver drifts into your lane, the safer escape is right onto the shoulder. Steering left risks a head-on if the other driver corrects.
A fully loaded tractor-trailer traveling at 55 mph on dry pavement requires roughly what total stopping distance (perception + reaction + braking)?
Correct. Total stopping distance for a heavy commercial vehicle at 55 mph on dry pavement is approximately 300 feet, or the length of a football field including end zones.
Doubling your speed roughly:
Correct. Braking distance is proportional to the square of speed. Doubling speed roughly quadruples braking distance.
When driving down a long, steep downgrade, you should:
Correct. Select a low gear before starting down. Use the brakes in firm, intermittent applications: brake until 5 mph below safe speed, release until safe speed is regained, repeat. Continuous brake application overheats the brakes.
A driver-side skid can cause a tractor-trailer to:
Correct. When the drive wheels lose traction and the trailer continues forward, the tractor pivots and the rig jackknifes.
To recover from a drive-wheel skid, you should:
Correct. Stop applying power, push in the clutch (or shift to neutral) to let the wheels turn freely, and counter-steer in the direction you want the front of the vehicle to go.
Which of the following is true about driving at night?
Correct. Drive at a speed where your stopping distance does not exceed the distance you can see — typically 250 feet on low beams, 350-500 feet on high beams.
What is the minimum amount of tread depth required on tires other than front (steering) tires?
Correct. Non-steer tires must have at least 2/32-inch tread depth in every major groove.
Which of the following is the best way to prevent a fire in your vehicle?
Correct. Most fires are preventable through inspection (electrical, fuel-system, tire) and watching gauges, plus prohibiting smoking near fuel and observing safe loading/refueling rules.
Which type of fire extinguisher should you use on an electrical fire?
Correct. Class B:C dry-chemical extinguishers (often labeled "B:C" or "ABC") are appropriate for electrical fires. Never use water on an electrical fire.
When approaching a railroad crossing, drivers of buses, school buses, and placarded hazmat vehicles must:
Correct. Buses, school buses, and placarded hazmat vehicles must stop at every crossing, 15 to 50 feet from the nearest rail. Look and listen, then proceed when safe.
Which lane is generally the best for a commercial vehicle on a multi-lane highway?
Correct. The right lane is generally best — it limits lane changes, reduces conflict with merging traffic only on the right, and matches commercial-vehicle speed.
Which of the following can cause the wheels of your vehicle to skid on a curve?
Correct. Posted curve advisory speeds assume cars; a heavy commercial vehicle with a high center of gravity may roll over or skid even at the posted speed. Slow before the curve, accelerate gently through it.
When you double your speed from 20 to 40 mph, the impact in a crash is:
Correct. Crash energy is proportional to the square of speed. Doubling speed quadruples the energy of impact.
A driver who has been disqualified is:
Correct. A disqualified driver may not operate a commercial motor vehicle on public roads, regardless of supervision.
Which of these is a major cause of crashes in heavy vehicles?
Correct. Fatigue, heavy traffic, and following too closely are all leading factors in commercial vehicle crashes.
What is "black ice"?
Correct. Black ice is a thin, clear sheet of ice that looks like wet pavement. Suspect it whenever the temperature is at or below freezing and the road appears wet.
You are driving on a wet road. To test how slippery the road is, you can:
Correct. At low speed and in a safe place, you can gently test traction by lightly applying the brakes or by gently accelerating. Hard braking at high speed is dangerous.
Communicating your intention to other drivers is best accomplished by:
Correct. Use turn signals well before turning or changing lanes. Brake lights, four-way flashers, and headlights also help communicate.
The four-way flashers on a commercial vehicle should be used:
Correct. Use four-way flashers anytime your vehicle is stopped on or near the roadway, or moving slowly enough that approaching traffic might be surprised.
Which of these is the best advice for staying alert on a long trip?
Correct. Adequate sleep before driving and scheduled rest breaks are the only reliable strategies. Coffee and cold air mask fatigue but do not eliminate it.
Most drivers who fall asleep at the wheel:
Correct. Most drivers who fall asleep do not realize how drowsy they are. The only fix is to stop and rest before fatigue reaches that point.
What does it mean when a driver is "hydroplaning"?
Correct. Hydroplaning means tires have lost contact with the pavement and are riding on standing water. Steering and braking become ineffective.
When should you use your high beams?
Correct. Federal and state law requires you to dim high beams when within 500 feet of an oncoming vehicle, or when following within 500 feet of another vehicle.
Empty trucks:
Correct. An empty truck has lighter axle weight, so the brakes generate less friction relative to vehicle weight — the truck can take longer to stop than the same vehicle loaded.
When a vehicle ahead of you brakes hard, you should:
Correct. Plan your escape: identify a clear lane or shoulder. If you can steer to safety, you save reaction time. If not, brake firmly without locking the wheels.
You are driving on a steep downgrade and your brakes have failed. The best escape is to:
Correct. If a runaway escape ramp is available, use it. Modern arrester beds use loose gravel or sand to slow the vehicle without injury to the driver.
Which of the following is true about the front-end shock absorbers?
Correct. Shock absorbers control suspension oscillation. Worn shocks contribute to poor handling, uneven tire wear, and reduced control on rough roads.
Which of the following is a cab in-vehicle inspection item?
Correct. Steering-wheel free play is checked from the driver seat and should not exceed 10 degrees (about 2 inches on a 20-inch wheel).
Maximum allowable steering-wheel play is approximately:
Correct. Steering wheel play should not exceed 10 degrees (roughly 2 inches on a 20-inch wheel). More than that, the vehicle is hard to steer.
When approaching a downgrade, you should select:
Correct. Select your gear before the downgrade — modern transmissions can be hard or impossible to shift into a lower gear once you are descending and engine RPM has dropped.
Which is the proper position for your hands on the steering wheel?
Correct. Both hands should be on opposite sides of the wheel — typically the 9 o'clock and 3 o'clock positions — for steering control.
Stopping distance increases significantly when:
Correct. Wet brakes, worn tires, heavy load, and slick pavement all extend stopping distance. Plan ahead and follow at greater intervals.
You should never drive your vehicle if the brake-system warning device:
Correct. A continuously lit or sounding low-air warning means dangerous brake-system pressure loss. Stop safely and have the system serviced.
A driver convicted of driving a CMV with a BAC of .04 or higher faces:
Correct. A first conviction of driving a CMV with BAC ≥ .04 disqualifies the driver for at least one year (three years if hauling hazmat).
How can you tell if you are driving in mountains?
Correct. Mountain driving demands attention to grade-related challenges: gear selection on upgrades, speed control on downgrades, escape ramp awareness.
A driver should look down the road how far when driving at highway speeds?
Correct. Look 12-15 seconds ahead — about a quarter mile at highway speeds. This gives time to identify and react to hazards.
You should test your brakes before going down a hill by:
Correct. Just before the descent, gently apply the brakes at slow speed to confirm response. Combined with selecting a low gear in advance, this is the safe practice.
Which of these statements about backing a heavy vehicle is true?
Correct. Backing is always risky for heavy vehicles. Use a helper, communicate with hand signals agreed in advance, back slowly, and if alone, get out and look (G.O.A.L.).
You should back from the driver's side rather than the passenger's side when possible because:
Correct. Driver-side ("sight side") backing gives the driver direct visual feedback through the open window in addition to mirror checks.
Aggressive driving includes:
Correct. Aggressive driving covers tailgating, lane weaving, excessive speed, running red lights, and other reckless behaviors. Avoid both committing and reacting to it.
When merging onto a highway, you should:
Correct. Use the on-ramp to accelerate to traffic speed and merge into an existing gap. Stopping at the end of an on-ramp is dangerous.
Which of these is the best way to communicate that you are slowing down?
Correct. Lightly tapping the brake pedal flashes the brake lights, alerting drivers behind that you are slowing.
When should you use four-way flashers?
Correct. Four-way emergency flashers warn other drivers when your vehicle is stopped or moving slowly relative to traffic.
Which of these is NOT a hazard you should look out for ahead?
Correct. Hazards are conditions that could lead to a crash: pedestrians, stopped vehicles, work zones, debris. A clear, dry road is the absence of a hazard.
You are driving in a work zone. You should:
Correct. Work-zone fines double or more in most states. Slow down, give the vehicle ahead extra space, watch for workers and equipment, and follow signed speed reductions.
A vehicle's "no zone":
Correct. The "no zone" is the set of blind spots around a truck — front, both sides (especially right), and rear — where other vehicles cannot be seen.
You should signal:
Correct. Signal early, signal long enough that other drivers see and process the signal, and cancel after the maneuver.
Which is the safest stopping technique for a non-ABS vehicle whose brakes have started to lock up?
Correct. On a non-ABS vehicle, stab braking — full brake application until wheels lock, release, repeat — keeps the vehicle straight while still slowing.
On a vehicle equipped with ABS, you should:
Correct. With ABS, brake the way you always would. The system prevents wheel lockup automatically; pumping interrupts ABS function.
When approaching a curve, you should:
Correct. Slow before entering the curve. Once in the curve, accelerate gently to maintain stability — braking in a curve invites a skid or rollover.
When driving in heavy fog, you should:
Correct. If visibility is so poor that you cannot drive safely, pull completely off the road, turn on four-way flashers, and wait for conditions to improve.
Wet brakes can cause:
Correct. After driving through deep water, brakes may be wet — they can lose effectiveness, pull to one side, or grab. Apply the brakes lightly while driving slowly to dry them.
A "controlled braking" stop is:
Correct. Controlled braking applies the brakes as hard as you can without locking the wheels — used in emergency stops on non-ABS vehicles to retain steering.
Which of the following is a good way to avoid hydroplaning?
Correct. Slowing down reduces the chance of hydroplaning. Maintain proper tire inflation and tread depth, and avoid using cruise control on wet roads.
Convex (curved or "fish-eye") mirrors:
Correct. Convex mirrors widen the field of view but distort distance — objects appear smaller and farther away than they are.
Cargo that is loaded too high:
Correct. A high center of gravity makes the vehicle prone to rollover on curves, ramps, and during evasive maneuvers. Stack heavier items low.
Cargo should be secured so that it does not shift:
Correct. Federal cargo-securement rules require that cargo not shift in any direction during normal driving conditions, including emergency braking.
Federal regulations require a tie-down for every cargo, with a minimum of:
Correct. The general rule: at least one tie-down per 10 feet of article, plus a minimum based on length and weight (commonly two minimum for items over 5 feet or 1,100 lbs).
When stopping at the scene of an accident, you should:
Correct. Park clear of the road, activate four-way flashers, set out warning triangles, and assist as you can without putting yourself in danger.
If you are involved in an accident, you should:
Correct. Stop, protect the scene, notify authorities, care for injured persons, and exchange the required information. Failing to stop is a serious offense.
A "convex mirror" on the side of a tractor:
Correct. Convex (curved) mirrors widen the field of view but distort distance perception — objects look smaller and farther than they actually are.
Which of these vehicles is most likely to have to stop at a railroad crossing?
Correct. Buses, school buses, and placarded hazmat vehicles must stop at every railroad crossing 15 to 50 feet from the nearest rail.
The "implied consent" rule means:
Correct. By holding a CDL and operating a CMV on public roads, you have given implied consent to alcohol and drug testing. Refusing testing leads to disqualification just as a positive test does.
Hazardous materials awareness is required for:
Correct. Every CDL applicant must understand basic hazmat awareness — recognizing placards, labels, and shipping papers — even if they never haul hazmat.
When you exit a highway in a heavy commercial vehicle, you should:
Correct. Posted ramp speeds assume passenger cars. A loaded heavy vehicle, especially with high CG, can roll over at the posted speed. Slow before the curve.
Which of these is true about following distance for heavy vehicles?
Correct. Greater weight = longer stopping distance. Use one second per 10 feet of vehicle length below 40 mph, plus an extra second above 40.
A safe practice when entering a freeway is to:
Correct. Use the on-ramp to match traffic speed before merging. Stopping at the end of an on-ramp is dangerous.
Cargo securement is the responsibility of:
Correct. The driver is ultimately responsible for verifying that cargo is properly secured before driving and remains secure throughout the trip.
A driver may resume driving after a 10-hour off-duty period only if:
Correct. HOS rules limit driving and on-duty hours within a fixed window. After 10 hours off-duty, driving may resume only if other limits also allow.
A driver who notices their vehicle is overweight should:
Correct. Overweight vehicles violate axle and gross-weight limits, damage roads, increase stopping distance, and incur fines. Adjust the load before continuing.
Driver fatigue is most often caused by:
Correct. Sleep deprivation, long hours, and circadian-low night-driving hours are the leading causes of fatigue. Sleep before driving; pull over when drowsy.
When you arrive at a customer to deliver:
Correct. Customer sites have their own safety rules — sign in, wear required PPE, follow speed limits and designated routes.
When the brake pedal feels spongy on an air-brake vehicle:
Correct. A spongy or unusual feel in air-brake pedals indicates a system issue. Have it inspected before continuing.
On a tight curve in a rural mountain road:
Correct. Mountain curves often have advisory speeds well below your safe load speed. Slow before entering and use the full lane safely.
A "low-clearance" warning sign requires the driver to:
Correct. Verify your vehicle's height. Hitting a low-clearance bridge or overpass is dangerous and expensive — and entirely the driver's responsibility.
Speed control on long downgrades is best maintained by:
Correct. Pre-select a low gear, use engine braking, and apply brakes in firm intermittent pulses. This prevents brake fade.
You are about to begin a trip and notice the dashboard low-air warning is on. You should:
Correct. Allow pressure to build, the warning to clear, and complete the seven-step air-brake check before driving.
A tire may need replacement if:
Correct. Below-minimum tread depth, sidewall damage, exposed cords, bulges, or excessive wear are all reasons to replace.
When backing into a tight space, the driver should:
Correct. G.O.A.L. — Get Out And Look — is the universal driver-school rule. When in doubt, stop and look. Use a helper when available.