56 General Knowledge Practice Questions & Answers
Every General Knowledge practice question from the CDL Practice Test, with the correct answer and a short explanation.
Start practice test →1. At what blood alcohol concentration (BAC) is a CDL driver considered legally intoxicated while operating a commercial motor vehicle?
- A.0.08
- B.0.02
- C.0.10
- D.0.04✓ Answer
A CDL driver operating a CMV with a BAC of 0.04 or higher is considered intoxicated, half the 0.08 limit for regular drivers.
2. During a pre-trip inspection, why should you check the engine oil, coolant, and other fluid levels?
- A.To find and correct problems before they cause a breakdown or crash✓ Answer
- B.Because low fluids improve fuel economy
- C.Only to satisfy the DMV examiner
- D.It is only required for vehicles over 10 years old
The purpose of a pre-trip inspection is to find problems that could cause a breakdown or crash and fix them before driving.
3. When driving a heavy vehicle in normal, dry conditions, how far ahead should you look while driving?
- A.About 1 to 2 seconds ahead
- B.Just in front of the bumper
- C.At least 60 seconds ahead
- D.12 to 15 seconds ahead✓ Answer
You should look 12 to 15 seconds ahead, which at highway speeds is about a quarter of a mile.
4. What is the proper way to stop a vehicle when braking normally (not in an emergency)?
- A.Push the brake pedal down and ride it lightly all the way
- B.Apply steady, firm pressure without locking the wheels✓ Answer
- C.Pump the brakes rapidly the entire stop
- D.Slam the brakes hard once then release
Brake so the vehicle stays in a straight line and can be stopped smoothly, applying firm steady pressure without locking the wheels.
5. On a long, steep downgrade, what is the most important thing to do to control your speed?
- A.Shift into neutral to coast down and save the brakes
- B.Select a low gear before starting down and use engine braking✓ Answer
- C.Rely mainly on the service brakes the whole way down
- D.Keep the transmission in the highest gear possible
Select a low gear before starting down a grade so engine braking helps control speed and the brakes don't overheat and fade.
6. An escape ramp (runaway ramp) on a mountain downgrade is designed to do what?
- A.Allow trucks to make a legal U-turn
- B.Stop a vehicle safely when its brakes have failed✓ Answer
- C.Provide a place to rest and check cargo
- D.Serve as a lane for slow-moving trucks
Escape ramps use soft gravel, and sometimes an upgrade, to stop a runaway vehicle safely when its brakes fail.
7. What should you do when your drive wheels start to skid?
- A.Apply the parking brake immediately
- B.Press harder on the accelerator to regain traction
- C.Stop braking or ease off the accelerator, then steer to stay on course✓ Answer
- D.Turn the wheel sharply in the opposite direction
To recover from a drive-wheel skid, stop braking or let up on the accelerator so the wheels can roll, then steer to keep the vehicle on course.
8. How far ahead do your headlights let you see when driving on low beams at night?
- A.About 1,000 feet
- B.About 250 feet✓ Answer
- C.About 100 feet
- D.About 500 feet
Low beams let you see about 250 feet ahead and high beams about 350-500 feet; you must be able to stop within the distance you can see, so you should not overdrive your headlights.
9. You are driving in dense fog. What is the best action to take?
- A.Turn off all lights to reduce glare
- B.Speed up to get out of the fog area quickly
- C.Slow down and use low beams; consider pulling off the road until it clears✓ Answer
- D.Turn on your high-beam headlights for maximum light
In fog, slow down, use low beams (high beams reflect back and reduce visibility), and if it is very thick, pull completely off the road and wait.
10. By about how much does stopping distance increase as speed increases, according to the principle in the CDL Manual?
- A.It decreases as the vehicle gets heavier
- B.It increases much faster than speed - roughly with the square of speed✓ Answer
- C.It stays roughly the same regardless of speed
- D.It increases by the same fixed number of feet each time
Braking distance grows with the square of speed, so doubling your speed roughly quadruples the braking distance.
11. Total stopping distance for a heavy vehicle is made up of which components?
- A.Reaction distance + tire wear
- B.Braking distance only
- C.Following distance + weather delay
- D.Perception distance + reaction distance + braking distance✓ Answer
Total stopping distance is the sum of perception distance, reaction distance, and braking distance.
12. How much following distance should you allow for a 40-foot vehicle traveling below 40 mph, using the seconds rule?
- A.At least 5 seconds
- B.At least 4 seconds✓ Answer
- C.At least 8 seconds
- D.1 second total
Allow 1 second per 10 feet of vehicle length below 40 mph, so a 40-foot vehicle needs at least 4 seconds of following distance.
13. To make sure you have enough space to change lanes safely, you should do what because of the 'No-Zone' blind spots?
- A.Change lanes only at night when traffic is lighter
- B.Rely only on your mirrors and change quickly
- C.Assume other drivers will move out of your way
- D.Check mirrors, signal early, and check that the lane is clear before moving over✓ Answer
Large vehicles have big blind spots (No-Zones); check mirrors, signal early, and make sure the lane is truly clear before changing lanes.
14. If your cargo is loaded with a high center of gravity, what danger does this create?
- A.The vehicle will steer more easily
- B.Braking distance will be shorter
- C.Fuel economy will improve significantly
- D.The vehicle is more likely to tip over, especially in curves✓ Answer
A high center of gravity makes a vehicle top-heavy and much more likely to tip over, particularly when going around curves or making quick maneuvers.
15. How often must you stop to check that your cargo and its securement are still secure on a trip?
- A.Only if you hear a noise
- B.Within the first 50 miles, then every 3 hours or 150 miles✓ Answer
- C.Only at the final destination
- D.Once per day at the end of the shift
You must inspect cargo securement within the first 50 miles and then re-check every 3 hours or 150 miles, or when you change duty status.
16. What is the purpose of hazardous materials placards on a commercial vehicle?
- A.To warn others of the hazard and communicate the risk to emergency responders✓ Answer
- B.To exempt the driver from weigh stations
- C.To increase the allowed cargo weight
- D.To advertise the trucking company
Placards are diamond-shaped warning signs that alert others and emergency responders to the type of hazardous material being carried.
17. Under the federal hours-of-service rules, after how many consecutive hours off duty may a property-carrying driver begin a new 14-hour driving window?
- A.8 consecutive hours
- B.14 consecutive hours
- C.6 consecutive hours
- D.10 consecutive hours✓ Answer
A property-carrying driver may drive again only after 10 consecutive hours off duty, which resets the 11-hour driving limit and 14-hour window.
18. Under federal hours-of-service rules, a property-carrying CDL driver may drive a maximum of how many hours after 10 hours off duty?
- A.14 hours
- B.11 hours✓ Answer
- C.10 hours
- D.8 hours
After 10 consecutive hours off duty, a property-carrying driver may drive up to 11 hours, but only within a 14-hour on-duty window.
19. Which of the following is an example of aggressive driving that a professional CDL driver should avoid?
- A.Signaling before every lane change
- B.Leaving extra following distance in the rain
- C.Slowing down for a work zone
- D.Tailgating and cutting off other vehicles in anger✓ Answer
Aggressive driving includes tailgating, cutting others off, and reacting in anger; professional drivers must stay calm and give other road users space.
20. Why is texting or using a hand-held phone especially dangerous and prohibited for CDL drivers while driving?
- A.It drains the truck's battery
- B.It is only a problem in city traffic
- C.It voids the vehicle warranty
- D.It takes your eyes, hands, and attention off the road and is banned by federal rule✓ Answer
Texting and hand-held phone use take your eyes, hands, and mind off driving and are prohibited for CMV drivers by FMCSA rules.
21. What are the three main types of vehicle inspection a commercial driver must perform?
- A.Pre-trip, en-route, and post-trip inspections✓ Answer
- B.Morning, noon, and evening inspections
- C.Engine, tire, and paint inspections
- D.Legal, financial, and mechanical inspections
Drivers do a pre-trip inspection before driving, en-route checks during the trip, and a post-trip inspection with a report at the end.
22. During an en-route inspection, which of the following should you monitor while driving?
- A.The radio station and cabin temperature only
- B.Instruments, gauges, and tire condition, watching for signs of trouble✓ Answer
- C.The color of the paint on nearby vehicles
- D.Nothing; en-route checks are not required
While driving, watch gauges and instruments and use your senses (look, listen, smell, feel) to catch problems such as tire or brake trouble.
23. When backing a heavy vehicle, what is the safest practice?
- A.Back quickly to get it over with
- B.Back and turn toward the right side so you can see better
- C.Rely only on your mirrors and never get out
- D.Back slowly, use both mirrors, and use a helper when possible✓ Answer
Back slowly using both mirrors; back toward the driver's (left) side when you can, and use a helper who stays in view to guide you.
24. When should you shift up to a higher gear in a manual-transmission truck?
- A.As engine speed (rpm) rises to the top of the operating range✓ Answer
- B.Whenever the vehicle is stopped
- C.Only when going downhill
- D.As soon as you start moving, regardless of speed
Use engine speed (rpm) and road speed to know when to shift; shift up as the engine reaches the top of its operating rpm range.
25. Why should you adjust and check your mirrors before starting a trip?
- A.So you can watch traffic behind and beside you and monitor your tires and cargo✓ Answer
- B.Because the law requires exactly five mirrors
- C.Only to check your own appearance
- D.Mirrors are decorative and need no adjustment
Properly adjusted mirrors let you see traffic to the sides and rear and monitor your own tires and cargo while driving.
26. How far ahead of a turn or lane change should you normally signal with a commercial vehicle?
- A.Only after you have started the maneuver
- B.There is no need to signal in a large truck
- C.Exactly one second before turning
- D.Signal early and keep signaling until the maneuver is complete✓ Answer
Signal early to communicate your intentions, and keep the signal on through the turn or lane change so other drivers know your plan.
27. When you must stop on the shoulder of the road, how should you use your warning devices?
- A.Do nothing; hazard flashers alone are always enough
- B.Wait an hour before placing any devices
- C.Turn on hazard flashers and place reflective triangles as required behind and ahead of the vehicle✓ Answer
- D.Place a single triangle directly under the truck
Turn on your hazard flashers and put out reflective triangles (or flares) at the required distances to warn approaching traffic.
28. What is a good rule for how much space you need to cross or enter traffic in a heavy vehicle?
- A.You need less space than a car because trucks are more visible
- B.Any gap is fine as long as you accelerate hard
- C.Space equals two car lengths in all cases
- D.You need a larger gap because a loaded truck accelerates slowly and needs more time to clear✓ Answer
Because a heavy vehicle accelerates slowly and is long, you need a much bigger gap in traffic to cross or merge safely.
29. Before driving under a bridge or through an underpass, why should you know your vehicle's height?
- A.To calculate fuel usage
- B.To make sure you have enough overhead clearance and don't strike the structure✓ Answer
- C.Height has no effect on driving
- D.Only to set the mirrors
You must know your vehicle's height and respect posted clearance signs so you have enough overhead clearance and do not hit a bridge or overpass.
30. What is 'perception distance' as part of total stopping distance?
- A.The distance the vehicle travels while the brakes physically slow it
- B.The distance between two axles
- C.The distance you can see with high beams
- D.The distance traveled from seeing a hazard until your brain recognizes it✓ Answer
Perception distance is how far the vehicle travels from the moment you see a hazard until your brain recognizes it.
31. How should you drive through a curve in a heavy vehicle?
- A.Brake hard in the middle of the curve
- B.Speed up before entering so you can coast through
- C.Slow to a safe speed before the curve, then accelerate gently through it✓ Answer
- D.Keep the exact posted highway speed no matter what
Slow to a safe speed before entering a curve, because braking in a curve can cause a skid or rollover; then accelerate gently through it.
32. In hot weather, why should you check your tires periodically on a long trip?
- A.Heat and high speed raise tire temperature and pressure, increasing the risk of a blowout✓ Answer
- B.Tires get lighter in the heat
- C.Hot tires improve steering
- D.Tire pressure never changes with temperature
Hot weather and sustained speed raise tire temperature and pressure; check tires regularly to reduce the chance of a blowout.
33. When roads are slippery from snow or ice, how should you adjust your driving?
- A.Maintain your normal speed and following distance
- B.Brake and steer sharply to test traction
- C.Reduce speed, increase following distance, and make gentle, gradual movements✓ Answer
- D.Use cruise control to keep speed steady
On snow or ice, slow down, leave much more following distance, avoid sudden actions, and do not use cruise control on slippery roads.
34. What is hydroplaning, and how can it be reduced?
- A.It is engine overheating; add coolant
- B.It is a type of legal weigh-station check
- C.It only happens to empty trailers and cannot be prevented
- D.Tires ride on a film of water and lose road contact; reduce it by slowing down✓ Answer
Hydroplaning is when tires lose contact with the road on a film of water; reduce it by slowing down and keeping tires properly inflated with good tread.
35. When approaching a railroad crossing, what is a safe practice for a commercial driver?
- A.Speed up to beat any approaching train
- B.Stop on the tracks if traffic is heavy ahead
- C.Slow down, look and listen, and never start across unless you can clear the tracks completely✓ Answer
- D.Shift gears while crossing the tracks
Slow down, look and listen for trains, and never start across the tracks unless you are sure you can get completely across without stopping; do not shift gears on the tracks.
36. Which vehicles must always stop at railroad crossings even when no train is visible?
- A.All empty flatbed trailers
- B.Buses carrying passengers and vehicles hauling certain hazardous materials✓ Answer
- C.Only vehicles made before the year 2000
- D.No commercial vehicle ever has to stop
Buses carrying passengers and trucks placarded for certain hazardous materials must stop at railroad crossings and check before proceeding.
37. On a long mountain downgrade, what is the main benefit of using engine braking or a retarder?
- A.It lets you turn off your headlights
- B.It increases the legal load limit
- C.It replaces the need to reduce speed at all
- D.It helps slow the vehicle so the service brakes don't overheat and fade✓ Answer
Engine braking and retarders help hold speed on downgrades so the service brakes stay cool and do not fade from overheating.
38. What is the safest way to identify hazards early while driving a commercial vehicle?
- A.Focus only on the vehicle directly ahead
- B.Watch only your speedometer
- C.Look far ahead and scan the whole scene, including the sides and mirrors✓ Answer
- D.Close following so you react faster
Seeing hazards early means looking far ahead and scanning the whole traffic scene, sides, and mirrors, so you have time to react.
39. Which is a warning sign of driver fatigue that means you should stop and rest?
- A.Feeling alert and comfortable
- B.Heavy eyelids, drifting in the lane, and trouble remembering the last few miles✓ Answer
- C.Getting better fuel economy
- D.Passing every vehicle on the road
Heavy eyelids, wandering in the lane, and not remembering the last stretch of road are signs of fatigue; stop and rest before continuing.
40. What is the best way to prevent fatigue before and during a long driving shift?
- A.Drink strong coffee instead of sleeping
- B.Drive faster to finish sooner
- C.Get enough sleep beforehand and take breaks; if drowsy, stop and rest✓ Answer
- D.Open the window and turn up the radio to stay awake indefinitely
Getting enough sleep before driving and taking rest breaks is the real fix; coffee and fresh air are not substitutes for sleep, so stop when drowsy.
41. How does alcohol affect a driver's ability to operate a commercial vehicle safely?
- A.It improves reaction time
- B.It has no effect below the legal limit
- C.It impairs judgment, reaction time, and coordination even at low levels✓ Answer
- D.It only affects vision, not decision-making
Alcohol impairs judgment, slows reaction time, and reduces coordination even at low levels, which is why the CDL limit is a strict 0.04 BAC.
42. Which of the following will actually lower a person's blood alcohol concentration?
- A.Only time; the body needs time to eliminate alcohol✓ Answer
- B.Drinking black coffee
- C.Taking a cold shower
- D.Eating a large meal
Only time lets the body eliminate alcohol; coffee, cold showers, and food do not speed up sobering or lower your BAC.
43. When is a HazMat endorsement required on your CDL?
- A.Whenever you drive at night
- B.When transporting hazardous materials in amounts that require the vehicle to be placarded✓ Answer
- C.Only when the truck weighs over 80,000 pounds
- D.Any time you cross a state line
A HazMat endorsement is required when you transport hazardous materials in quantities that require the vehicle to display placards.
44. What does GVWR (Gross Vehicle Weight Rating) refer to?
- A.The maximum total weight of a single vehicle including its load, set by the manufacturer✓ Answer
- B.The empty weight of the vehicle only
- C.The weight of the cargo alone
- D.The combined weight limit of a truck plus trailer
GVWR is the maximum total weight of a single vehicle plus its load, as specified by the manufacturer; the combined figure is the GCWR.
45. Why is proper weight distribution and axle loading important when loading cargo?
- A.It only matters for appearance
- B.It has no effect once the load is tied down
- C.Poor distribution can overload axles and make steering, braking, and handling dangerous✓ Answer
- D.It only affects fuel taxes
Bad weight distribution can overload an axle and make the vehicle hard to steer, slow to brake, and prone to tipping; keep each axle within its legal limit.
46. What is the main purpose of tie-downs, chains, or straps on a flatbed load?
- A.To make the load look organized
- B.To reduce wind resistance
- C.To connect the trailer to the tractor
- D.To secure the cargo so it cannot shift, fall off, or come loose in transit✓ Answer
Tie-downs, chains, and straps secure cargo so it cannot shift, fall off, or come loose while driving, which protects you and other road users.
47. If you are the first to arrive at the scene of a crash, what should you do first?
- A.Move all injured people immediately
- B.Protect the scene, warn other traffic, and call for help✓ Answer
- C.Leave right away to avoid liability
- D.Take photos before doing anything else
First protect the accident scene (park safely, use flashers and warning devices), warn oncoming traffic, then call for help; avoid moving the injured unless there is danger like fire.
48. Which type of fire extinguisher rating is generally suitable for electrical and burning-liquid fires?
- A.Class A only
- B.B:C (or A:B:C) rated extinguishers✓ Answer
- C.Water extinguishers only
- D.No extinguisher works on those fires
A B:C or A:B:C rated extinguisher works on burning liquids and electrical fires; never use water on an electrical or gasoline fire.
49. When using a fire extinguisher, from what position should you aim it?
- A.Stand downwind and aim at the top of the flames
- B.Aim high above the fire
- C.Spray from directly overhead
- D.Stay upwind, aim at the base of the fire, and sweep side to side✓ Answer
Stay upwind so smoke and heat blow away from you, aim at the base of the fire, and sweep side to side.
50. How does the weight of a heavily loaded vehicle affect its stopping distance?
- A.A loaded vehicle generally takes longer to stop than an empty one at the same speed✓ Answer
- B.Weight has no effect on stopping distance
- C.A heavier vehicle always stops faster
- D.Only tire brand affects stopping distance
More weight generally means a longer stopping distance; empty trucks can also stop poorly because they have less traction, but at highway speed a loaded truck needs more room to stop.
51. Why should you increase your following distance at night or in poor visibility?
- A.To save fuel
- B.Because you can see less and need more time and room to react to hazards✓ Answer
- C.Because the speed limit is higher at night
- D.There is no reason to change following distance
At night and in poor visibility you can see less and have less warning of hazards, so leave extra following distance to give yourself time to react.
52. What should you do before driving at night to see and be seen better?
- A.Dim the dashboard so it is fully dark
- B.Remove one headlight to save power
- C.Clean windshield, mirrors, and lights, and make sure all lights work✓ Answer
- D.Wear dark sunglasses
Clean your windshield, mirrors, and lights and make sure all lights work; dirty glass and weak lights greatly reduce night visibility.
53. What is the best way to keep a safe space to the sides of your commercial vehicle?
- A.Drive in the center of your lane and avoid traveling alongside others✓ Answer
- B.Hug the lane line closest to traffic
- C.Straddle two lanes so no one can pass
- D.Match the speed of the vehicle beside you and stay there
Keep to the center of your lane and avoid driving alongside other vehicles so you always have an escape path if someone drifts toward you.
54. During a post-trip inspection, what should the driver do about problems found?
- A.Ignore them until they get worse
- B.Fix them personally on the road regardless of training
- C.Complete a written report noting any defects so they can be repaired✓ Answer
- D.Report only problems with the paint
A post-trip inspection includes a written report (DVIR) listing any defects found so they can be repaired before the vehicle is used again.
55. Why should you keep a safe space behind your vehicle (avoid being tailgated)?
- A.Tailgaters help push you along to save fuel
- B.Space behind you is never your concern
- C.It lets you brake harder without warning
- D.A tailgater cannot stop as quickly as you can, raising the risk of a rear-end crash✓ Answer
A tailgater may not be able to stop as quickly as your heavy vehicle; increase your own following distance and avoid quick stops to reduce rear-end crash risk.
56. Which basic control skill helps you place a large vehicle accurately during low-speed maneuvers?
- A.Accelerating as fast as possible
- B.Keeping the wheel locked straight at all times
- C.Steering smoothly and using clutch and brakes gently for precise, controlled movement✓ Answer
- D.Ignoring the mirrors to focus straight ahead
Basic vehicle control means moving smoothly: steer gently, use the clutch and brakes with care, and go slowly so you can place the vehicle precisely.
Practice questions based on the AAMVA/FMCSA model CDL manual. Requirements vary by state — study your state's official CDL manual before your exam. Official CDL info →