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CDL General Knowledge Practice Test

Everyone applying for a Class A, B or C CDL takes this test first. 57 questions on following distance, stopping distance, emergencies, cargo securement, alcohol rules, inspections and hours of service. Your progress is saved on this device.

All 57 questions with answers

For reading through. Tap "Show answer" under a question to see the answer and the reason.

  1. You drive a 40-foot truck at 35 mph. What is the minimum following distance the CDL manual recommends?

    1. 4 seconds
    2. 2 seconds
    3. 5 seconds
    4. 8 seconds
    Show answer
    A. 4 seconds Below 40 mph, leave at least one second for every 10 feet of vehicle length. A 40-foot vehicle needs 4 seconds. (CDL manual)

  2. The same 40-foot truck is now doing 55 mph. How much following distance should you leave?

    1. 5 seconds
    2. 6 seconds
    3. 10 seconds
    4. 4 seconds
    Show answer
    A. 5 seconds Above 40 mph, add one second to the one-second-per-10-feet rule: 4 + 1 = 5 seconds. (CDL manual)

  3. How far ahead should you look while driving?

    1. As far as you can see
    2. 20 to 25 seconds
    3. 5 to 8 seconds
    4. 12 to 15 seconds
    Show answer
    D. 12 to 15 seconds Look 12 to 15 seconds ahead: the distance you will travel in that time. It gives you time to spot hazards and change lanes or slow down early. (CDL manual)

  4. At highway speed, 12 to 15 seconds of travel is about how far?

    1. A quarter of a mile
    2. 300 feet
    3. One mile
    4. Half a mile
    Show answer
    A. A quarter of a mile At highway speed 12 to 15 seconds is about a quarter of a mile. In town it is about a block and a half. (CDL manual)

  5. If you double your speed, your braking distance becomes about:

    1. Four times as long
    2. The same
    3. Twice as long
    4. Eight times as long
    Show answer
    A. Four times as long Braking distance grows with the square of speed. Double the speed and the vehicle needs about four times the distance to stop. (CDL manual)

  6. Total stopping distance is made up of:

    1. Perception distance, reaction distance and braking distance
    2. Braking distance only
    3. Perception distance and following distance
    4. Reaction distance and braking distance
    Show answer
    A. Perception distance, reaction distance and braking distance Perception (seeing and recognizing the hazard), reaction (moving your foot to the brake) and braking (the vehicle slowing to a stop). Air brakes add brake lag on top. (CDL manual)

  7. For an alert driver, perception time averages about:

    1. 4 seconds
    2. 1/4 second
    3. 1 3/4 seconds
    4. 3/4 second
    Show answer
    C. 1 3/4 seconds About 1 3/4 seconds to see and recognize a hazard. Reaction time, from recognizing it to pressing the brake, adds about 3/4 of a second more. (CDL manual)

  8. Hydroplaning can happen at speeds as low as:

    1. 60 mph
    2. 15 mph
    3. 30 mph
    4. 45 mph
    Show answer
    C. 30 mph With enough water on the road, tires can lose contact at about 30 mph. It is more likely with low tire pressure or worn tread. Release the accelerator and push in the clutch; do not brake. (CDL manual)

  9. You stop on the shoulder of a highway. How soon must your warning triangles be out?

    1. Within 30 minutes
    2. Within 5 minutes
    3. Within 10 minutes
    4. Only after dark
    Show answer
    C. Within 10 minutes As soon as possible, and in any case within 10 minutes of stopping. (49 CFR 392.22(b)(1))

  10. Stopped on a two-lane road with traffic in both directions, where do the three triangles go?

    1. One within 10 feet on the traffic side, one 100 feet behind, one 100 feet ahead
    2. All three behind the vehicle, 100, 200 and 300 feet back
    3. One 50 feet behind, one 50 feet ahead, one on the cab roof
    4. Two behind at 100 feet, one next to the vehicle
    Show answer
    A. One within 10 feet on the traffic side, one 100 feet behind, one 100 feet ahead One on the traffic side within 10 feet of the front or rear, one about 100 feet (40 paces) back toward approaching traffic, and one about 100 feet the other way. (49 CFR 392.22(b)(1))

  1. Stopped on a divided or one-way highway, where do the triangles go?

    1. 50, 100 and 150 feet toward approaching traffic
    2. One behind the vehicle only
    3. 100 feet ahead and 100 feet behind
    4. 10, 100 and 200 feet toward approaching traffic
    Show answer
    D. 10, 100 and 200 feet toward approaching traffic All three face the traffic coming up behind you: one within 10 feet of the rear on the traffic side, one at 100 feet and one at 200 feet. (49 CFR 392.22(b)(2)(v))

  2. You stop just past the crest of a hill. How far back should the rear warning device go?

    1. Right at your rear bumper
    2. At least 1,000 feet
    3. Exactly 50 feet
    4. Anywhere from 100 to 500 feet
    Show answer
    D. Anywhere from 100 to 500 feet Within 500 feet of a curve, hilltop or other obstruction, place the device toward the obstruction 100 to 500 feet from the vehicle, so drivers see it before they reach you. (49 CFR 392.22(b)(2)(iv))

  3. A vehicle that must stop at railroad crossings has to stop:

    1. Wherever the driver can see best
    2. Within 10 feet of the tracks
    3. Between 15 and 50 feet from the tracks
    4. Between 50 and 100 feet from the tracks
    Show answer
    C. Between 15 and 50 feet from the tracks Within 50 feet of the tracks and not closer than 15 feet, then look and listen both ways. Buses with passengers and many placarded hazmat vehicles must always stop. (49 CFR 392.10(a))

  4. While crossing railroad tracks you should:

    1. Shift up to clear the tracks faster
    2. Shift down to get more power
    3. Not shift gears at all
    4. Put the transmission in neutral
    Show answer
    C. Not shift gears at all Cross in a gear that gets you all the way over without changing. A missed shift on the tracks can leave you stalled there. (49 CFR 392.10(a))

  5. What is the minimum tread depth for tires on the steering (front) axle?

    1. 4/32 inch
    2. 6/32 inch
    3. 8/32 inch
    4. 2/32 inch
    Show answer
    A. 4/32 inch Front tires need at least 4/32 of an inch in every major groove. All other tires need 2/32. (49 CFR 393.75)

  6. What is the minimum tread depth for tires that are not on the front axle?

    1. 4/32 inch
    2. 1/32 inch
    3. 6/32 inch
    4. 2/32 inch
    Show answer
    D. 2/32 inch 2/32 of an inch measured in a major tread groove. (49 CFR 393.75)

  7. During the pre-trip inspection, how much steering wheel play is too much?

    1. More than 10 degrees, about 2 inches on a 20-inch wheel
    2. Any play at all
    3. More than a quarter turn
    4. More than 45 degrees
    Show answer
    A. More than 10 degrees, about 2 inches on a 20-inch wheel More than 10 degrees of free play (about 2 inches at the rim of a 20-inch wheel) makes the vehicle hard to steer. (CDL manual)

  8. Rust streaks around the lug nuts on a wheel usually mean:

    1. The tire is under-inflated
    2. The wheel was recently painted
    3. The lug nuts may be loose
    4. Nothing important
    Show answer
    C. The lug nuts may be loose Rust trails from lug nuts are a sign they are loose and moving. Check them before driving. (CDL manual)

  9. After starting a trip, you must inspect your cargo and its securement within the first:

    1. 50 miles
    2. 150 miles
    3. 100 miles
    4. 25 miles
    Show answer
    A. 50 miles Within the first 50 miles, and adjust or add securement if anything has moved. (49 CFR 392.9(b)(2))

  10. After the first check, cargo securement must be rechecked:

    1. Every 3 hours or 150 miles, whichever comes first
    2. Every 500 miles
    3. Only at the end of the trip
    4. Every 8 hours
    Show answer
    A. Every 3 hours or 150 miles, whichever comes first Also whenever your duty status changes. Whichever of 3 hours of driving or 150 miles comes first. (49 CFR 392.9(b)(3))

  11. The combined working load limit of the tiedowns on a piece of cargo must be at least:

    1. One half of its weight
    2. One quarter of its weight
    3. Equal to its weight
    4. Twice its weight
    Show answer
    A. One half of its weight The aggregate working load limit of the tiedowns must be at least one-half times the weight of the article or group of articles. (49 CFR 393.106(d))

  12. An article 12 feet long, with nothing blocking it at the front, needs at least how many tiedowns?

    1. 3
    2. 4
    3. 2
    4. 1
    Show answer
    A. 3 Two tiedowns for the first 10 feet, plus one more for every 10 feet or part of 10 feet beyond that. 12 feet: 2 + 1 = 3. (49 CFR 393.110(b)(3))

  13. A CDL driver is legally under the influence in a commercial vehicle at a blood alcohol concentration of:

    1. 0.08
    2. 0.02
    3. 0.10
    4. 0.04
    Show answer
    D. 0.04 In a commercial motor vehicle the limit is 0.04, half the 0.08 that applies in a car. (49 CFR 383.51(b))

  14. How long before going on duty or driving a CMV must you not drink any alcohol?

    1. 2 hours
    2. 1 hour
    3. 8 hours
    4. 4 hours
    Show answer
    D. 4 hours No alcohol within 4 hours before going on duty or operating a commercial motor vehicle. (49 CFR 392.5(a)(1))

  15. A driver is found with any detectable alcohol, but under 0.04, while on duty. What happens?

    1. CDL suspended for 1 year
    2. Nothing, it is under the limit
    3. Out of service for 24 hours
    4. A warning only
    Show answer
    C. Out of service for 24 hours Any measurable alcohol, or being under its influence, puts the driver out of service immediately for 24 hours. (49 CFR 392.5(c))

  1. First conviction for driving a CMV at 0.04 or more, not carrying hazmat. The disqualification is:

    1. 6 months
    2. Life
    3. 1 year
    4. 60 days
    Show answer
    C. 1 year One year for a first offense. Three years if the vehicle was carrying placarded hazardous materials. (49 CFR 383.51(b))

  2. Refusing an alcohol test when a police officer requests one is treated:

    1. As a warning on your record
    2. As no offense if you were sober
    3. As a minor traffic ticket
    4. The same as driving under the influence
    Show answer
    D. The same as driving under the influence Refusal is listed alongside the alcohol offenses in the disqualification table: a first refusal costs the CDL for one year. (49 CFR 383.51(b))

  3. While driving a CMV, which of these is allowed?

    1. Holding the phone to your ear
    2. Dialing a 10-digit number by hand
    3. Reading a text message at a red light
    4. Pressing a single button to start or end a call on a mounted phone
    Show answer
    D. Pressing a single button to start or end a call on a mounted phone Texting and hand-held phone use are banned while driving, including when stopped in traffic. Pressing a single button to start or end a voice call is the exception. (49 CFR 392.80, 392.82)

  4. Most serious skids are caused by:

    1. Driving too fast for road conditions
    2. Brake failure
    3. Bald tires
    4. Cross winds
    Show answer
    A. Driving too fast for road conditions Over-braking, over-steering and over-acceleration all cause skids, but most serious skids come from driving too fast for the conditions. (CDL manual)

  5. Your drive wheels start to skid. What should you do first?

    1. Steer sharply the other way
    2. Brake hard
    3. Shift to a higher gear
    4. Stop braking or accelerating and push in the clutch
    Show answer
    D. Stop braking or accelerating and push in the clutch Take away what caused the skid: release the brake or accelerator and push in the clutch so the wheels can roll freely, then steer where you want to go. (CDL manual)

  6. Stab braking (on a vehicle without ABS): after you release the brakes when the wheels lock, when do you apply them again?

    1. Only when the vehicle has stopped skidding sideways
    2. Immediately
    3. When the wheels start rolling again
    4. After 5 seconds
    Show answer
    C. When the wheels start rolling again Brake fully, release when the wheels lock, and reapply as soon as they start rolling. Wheels need about a second to start rolling after release. (CDL manual)

  7. Your vehicle has anti-lock brakes (ABS). In a hard stop you should:

    1. Brake as you normally would and let ABS prevent wheel lock
    2. Use only the trailer hand valve
    3. Pump the brakes quickly
    4. Brake with the parking brake
    Show answer
    A. Brake as you normally would and let ABS prevent wheel lock ABS stops the wheels locking; it does not shorten the stop. Brake normally with steady pressure and do not pump. (CDL manual)

  8. The ABS malfunction lamp stays on after the bulb check. This means:

    1. The ABS may not be working
    2. The service brakes have failed
    3. The parking brake is set
    4. ABS is working normally
    Show answer
    A. The ABS may not be working The lamp should go out after the start-up check. If it stays on or comes on while driving, the ABS may not be working, though the normal brakes still work. (CDL manual)

  9. When should you shift into a lower gear for a long, steep downgrade?

    1. Only if the brakes start to fade
    2. Halfway down, once you pick up speed
    3. At the bottom
    4. Before you start down the grade
    Show answer
    D. Before you start down the grade Get into the low gear before you start down. Trying to downshift once the vehicle has picked up speed may not work, and you can end up in neutral. (CDL manual)

  10. Your safe speed on a downgrade is 40 mph. With the recommended snub-braking method, you apply the brakes at 40 mph and release them at:

    1. 20 mph
    2. 30 mph
    3. 35 mph
    4. 38 mph
    Show answer
    C. 35 mph Brake firmly until you are about 5 mph under your safe speed, then release. The application should last about 3 seconds. Repeat when you are back at the safe speed. (CDL manual)

  11. Brake fade is mostly caused by:

    1. Excessive heat from using the brakes too much
    2. Low tire pressure
    3. Cold weather
    4. Worn shock absorbers
    Show answer
    A. Excessive heat from using the brakes too much Overused brakes heat up and lose stopping power. That is why the engine braking of a low gear, not the brakes, should control speed on long grades. (CDL manual)

  12. What is an escape ramp for?

    1. Stopping runaway vehicles safely
    2. Chain-up area in winter
    3. Letting faster traffic pass
    4. Parking overnight on mountain roads
    Show answer
    A. Stopping runaway vehicles safely Escape ramps use deep loose gravel or an uphill grade to stop a runaway vehicle. If your brakes fail on a grade, use one. (CDL manual)

  13. On a wet, icy or snow-covered road, the retarder should be:

    1. Used instead of the brakes
    2. Turned off
    3. Used only on the steer axle
    4. Set to its highest setting
    Show answer
    B. Turned off A retarder slows the drive wheels and can make them skid on a slippery road. Turn it off when the road is wet, icy or snowy. (CDL manual)

  14. Making a tight right turn, you should:

    1. Keep the rear of the vehicle close to the curb and turn wide as you complete the turn
    2. Turn sharply at the start of the turn
    3. Swing wide to the left before turning
    4. Turn from the left lane
    Show answer
    A. Keep the rear of the vehicle close to the curb and turn wide as you complete the turn Keeping the rear close to the curb stops cars squeezing in on your right. Go straight into the intersection and swing wide as you finish the turn, not before it. (CDL manual)

  15. When you have to back up, why is it best to back toward the driver's side?

    1. You can see what you are backing into
    2. It is easier on the tires
    3. It uses less fuel
    4. It is required by law
    Show answer
    A. You can see what you are backing into Backing toward the driver's side lets you watch the rear of the vehicle through the side window. Use a helper when you can. (CDL manual)

  1. Why can an empty truck need a longer stopping distance than a loaded one?

    1. It cannot; empty trucks always stop shorter
    2. The brakes are designed for a full load
    3. Empty trucks go faster
    4. An empty vehicle has less traction
    Show answer
    D. An empty vehicle has less traction The stiff suspension and strong brakes are designed for heavy loads. Empty, the wheels have less weight on them and less traction, and they can lock up. (CDL manual)

  2. At night you should dim your high beams when an oncoming vehicle is within:

    1. 1,000 feet
    2. 100 feet
    3. 200 feet
    4. 500 feet
    Show answer
    D. 500 feet Dim them within 500 feet of an oncoming vehicle so you do not blind its driver. Some states set more distances; follow your state handbook. (CDL manual)

  3. You are getting drowsy on the road. What actually fixes it?

    1. Sleep
    2. Coffee
    3. Opening the window
    4. Loud music
    Show answer
    A. Sleep Only sleep cures fatigue. Coffee and fresh air might help for a few minutes at most. Stop somewhere safe and rest. (CDL manual)

  4. A tire is on fire. What is the best way to deal with it?

    1. Water, and lots of it
    2. Let it burn out
    3. Drive on to put it out with air flow
    4. A B:C extinguisher
    Show answer
    A. Water, and lots of it Burning tires need to be cooled, which takes a lot of water. A dry-chemical extinguisher may put out the flames only for the tire to reignite. (CDL manual)

  5. A Class B fire involves:

    1. Electrical equipment only
    2. Wood, paper and cloth
    3. Metals
    4. Flammable liquids such as fuel and grease
    Show answer
    D. Flammable liquids such as fuel and grease Class A: ordinary combustibles. Class B: flammable liquids and grease. Class C: electrical. A B:C extinguisher covers the two you are most likely to meet on a truck. (CDL manual)

  6. Convex (curved) mirrors make objects look:

    1. Smaller and farther away than they are
    2. Upside down
    3. Larger and closer than they are
    4. Exactly as they are
    Show answer
    A. Smaller and farther away than they are Convex mirrors show a wider area but everything looks smaller and farther away. Remember that when judging a gap. (CDL manual)

  7. Which rides higher: an empty truck or the same truck fully loaded?

    1. They are the same height
    2. The loaded truck
    3. The empty truck
    4. It depends on the tires only
    Show answer
    C. The empty truck Weight pushes the suspension down. An empty truck can be higher than a loaded one, so a clearance that worked loaded may not work empty. (CDL manual)

  8. You must leave the road to avoid a crash. What should you do?

    1. Avoid braking until your speed drops to about 20 mph, then brake gently
    2. Put the transmission in neutral
    3. Steer back onto the road immediately at full speed
    4. Brake hard as soon as you leave the pavement
    Show answer
    A. Avoid braking until your speed drops to about 20 mph, then brake gently Hard braking on a soft shoulder can cause a skid. Keep one set of wheels on the pavement if you can, let the speed come down to about 20 mph, then brake gently and return to the road carefully. (CDL manual)

  9. In most emergencies, compared with stopping, you can steer to avoid a hazard:

    1. Never safely
    2. Just as quickly
    3. More quickly
    4. More slowly
    Show answer
    C. More quickly You can usually steer around an obstacle faster than you can stop for it. Top-heavy vehicles and tractors with multiple trailers can roll over, so steer carefully. (CDL manual)

  10. Someone is tailgating you. What is the right response?

    1. Flash your brake lights
    2. Increase the space ahead of you and avoid quick changes
    3. Speed up to get away
    4. Slow down sharply to warn them
    Show answer
    B. Increase the space ahead of you and avoid quick changes More space ahead means you will not have to stop suddenly with someone on your bumper. Avoid fast changes of speed or lane; turn on your four-ways only if needed. (CDL manual)

  11. After 10 consecutive hours off duty, a property-carrying driver may drive at most:

    1. 10 hours
    2. 14 hours
    3. 11 hours
    4. 8 hours
    Show answer
    C. 11 hours 11 hours of driving, inside a 14-hour window that starts when the driver comes on duty. (49 CFR 395.3(a)(3))

  12. A property-carrying driver may not drive beyond the ___ hour after coming on duty.

    1. 16th
    2. 14th
    3. 11th
    4. 12th
    Show answer
    B. 14th The 14-hour window runs from the start of the shift and does not stop for breaks, meals or waiting time. (49 CFR 395.3(a)(2))

  13. A 30-minute break is required after how much driving time?

    1. 11 hours
    2. 4 hours
    3. 6 hours
    4. 8 hours
    Show answer
    D. 8 hours After 8 hours of driving without a 30-minute interruption. The break can be off duty, sleeper berth or on duty not driving. (49 CFR 395.3(a)(3)(ii))

  14. For a carrier that operates every day of the week, the weekly limit is:

    1. 70 hours in 8 days
    2. 60 hours in 7 days
    3. 80 hours in 8 days
    4. 70 hours in 7 days
    Show answer
    A. 70 hours in 8 days 70 hours on duty in any 8 consecutive days. Carriers that do not operate every day use 60 hours in 7 days. 34 consecutive hours off resets either. (49 CFR 395.3(b))

  15. When is a property-carrying driver required to write a driver vehicle inspection report (DVIR) at the end of the day?

    1. Once a week
    2. Only after a crash
    3. Only when a defect or deficiency was found or reported
    4. Every day, for every vehicle
    Show answer
    C. Only when a defect or deficiency was found or reported The report lists defects that would affect safe operation. Drivers of property-carrying vehicles do not have to prepare one if no defect was found or reported. (49 CFR 396.11(a)(2))

  1. A driver must wear the seat belt:

    1. Only when carrying passengers
    2. Whenever the vehicle has one at the driver's seat
    3. Only on highways
    4. Only in states with a seat belt law
    Show answer
    B. Whenever the vehicle has one at the driver's seat A driver may not operate a CMV with a seat belt installed at the driver's seat unless wearing it. (49 CFR 392.16)

  2. You should slow down for a curve:

    1. Only if the road is wet
    2. In the middle of the curve
    3. Before you enter the curve
    4. As you leave the curve
    Show answer
    C. Before you enter the curve Brake before the curve and keep a steady speed or accelerate slightly through it. Braking in a curve can lock the wheels and cause a skid. Posted curve speeds may be too fast for a truck. (CDL manual)

The other practice tests