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CDL sample questions, with worked answers

Here are 21 original CDL-style questions covering the three Class A permit tests, with the answer and the rule under each: 8 General Knowledge, 7 Air Brakes and 6 Combination Vehicles. Try each one before you open the answer; the trap under it is the mistake most people make.

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Last checked · Original questions written for LifeScore from the state CDL manual, not DMV items

By the LifeScore Editorial Team · Updated · How we check facts · How this is scored

What do CDL General Knowledge questions look like?

Questions about a rule or a situation on the road: following distance, inspection defects, skids, emergencies and cargo. The first is worked in full; the rest open when you tap.

  1. CDL-style question 1 · Skids

    What is the most common type of skid?

    1. AA drive-wheel skid, when the rear drive wheels lose traction
    2. BA front-wheel skid
    3. CA trailer skid
    4. DA four-wheel skid
    Worked answer

    A: A drive-wheel skid, when the rear drive wheels lose traction. Drive-wheel skids, often from braking or accelerating too hard, are the most common.

    The trap: Picking "a trailer skid" because jackknifes are the famous image. The manual says drive-wheel skids are the most common.

  2. CDL-style question 2 · Basic control

    An automatic transmission lets you select a low gear manually. When is this useful?

    1. AWhen parking
    2. BOn flat highways at full speed
    3. CGoing down steep grades, to get engine braking
    4. DTo start on dry pavement
    Show the answer

    C: Going down steep grades, to get engine braking. Selecting a low range keeps the transmission from upshifting and adds engine braking on downgrades.

    The trap: Thinking low gears are only for starting. On an automatic, holding a low range on a downgrade is what gives you engine braking.

  3. CDL-style question 3 · License class

    A truck with a GVWR of 36,000 lb is towing a trailer with a GVWR of 4,000 lb. It carries no passengers and no placarded hazardous materials. Which CDL class does the driver need?

    1. ANo CDL class by weight alone
    2. BClass A
    3. CClass B
    4. DClass C
    Show the answer

    C: Class B. The power unit alone is rated 36,000 lb (26,001 lb or more), and the towed unit is rated 4,000 lb, not over 10,000 lb, so this is Class B. Class A: GCWR of 26,001 lb or more with a towed unit over 10,000 lb. Class B: a single vehicle of 26,001 lb or more, towing 10,000 lb or less.

  4. CDL-style question 4 · Stopping distance

    Your reaction time is 1.5 seconds. At 45 mph, about how far does the vehicle travel during the reaction time? (1 mph is about 1.47 feet per second.)

    1. A66 feet
    2. B124 feet
    3. C68 feet
    4. D99 feet
    Show the answer

    D: 99 feet. 45 mph × 5,280 ÷ 3,600 = 66 feet per second. × 1.5 s = 99, about 99 feet. Multiplying the mph by the seconds (67.5) forgets to change miles per hour to feet per second.

  5. CDL-style question 5 · Stopping distance

    Your reaction time is 1.5 seconds. At 50 mph, about how far does the vehicle travel during the reaction time? (1 mph is about 1.47 feet per second.)

    1. A55 feet
    2. B75 feet
    3. C135 feet
    4. D110 feet
    Show the answer

    D: 110 feet. 50 mph × 5,280 ÷ 3,600 = 73.3 feet per second. × 1.5 s = 110, about 110 feet. Multiplying the mph by the seconds (75) forgets to change miles per hour to feet per second.

  6. CDL-style question 6 · Following distance

    You are driving a 70-foot combination at 50 mph on a dry road. By the CDL manual's rule, at least how many seconds should you leave between you and the vehicle ahead?

    1. A7 seconds
    2. B8 seconds
    3. C5 seconds
    4. D10 seconds
    Show the worked answer

    B: 8 seconds. One second for each 10 feet of length is 7 seconds, and you add 1 second because you are above 40 mph: 8 seconds.

    1. Length: 70 ÷ 10 = 7 seconds.
    2. Speed is over 40 mph, so add 1 second.
    3. 7 + 1 = 8 seconds.

    The trap: Stopping at 7. The extra second above 40 mph is the part of the rule people forget.

  7. CDL-style question 7 · Hazards

    You stop on the shoulder of a two-lane road with traffic both ways. Where should your three warning triangles go?

    1. AAll three behind you, 10, 100 and 200 feet back
    2. BOne within 10 feet of the vehicle on the traffic side, one about 100 feet behind and one about 100 feet ahead
    3. COne beside each front tire and one at the rear
    4. DOne 500 feet behind you and two at the vehicle
    Show the worked answer

    B: One within 10 feet of the vehicle on the traffic side, one about 100 feet behind and one about 100 feet ahead. On a two-way road, traffic can come from either side, so you protect both directions: one by the vehicle, one about 100 feet behind and one about 100 feet ahead.

    1. Ask which way traffic comes from: both ways on a two-lane road.
    2. So you need a triangle ahead as well as behind.
    3. Pattern: within 10 feet, then about 100 feet in each direction.

    The trap: The 10-100-200 pattern is for one-way or divided roads, where all traffic comes from behind.

  8. CDL-style question 8 · Tires

    During your pre-trip inspection, a front (steering) tire has 3/32 inch of tread in its major grooves. What should you do?

    1. ADrive; 2/32 inch is the minimum
    2. BDrive; any visible tread is legal
    3. CDo not drive; front tires need at least 4/32 inch
    4. DDo not drive; every tire needs at least 6/32 inch
    Show the worked answer

    C: Do not drive; front tires need at least 4/32 inch. Federal rules (49 CFR 393.75) require at least 4/32 inch on front tires and 2/32 inch on the others. 3/32 is below the front-tire minimum.

    1. Find the tire position: front (steering).
    2. Front minimum: 4/32 inch. Others: 2/32 inch.
    3. 3/32 is under 4/32, so the tire must be replaced before driving.

    The trap: Using the 2/32 rule for every tire. The steering tires get the stricter limit because a front blowout is the hardest to control.

What do CDL Air Brakes questions look like?

Questions on the parts of the system, the pressures and limits in the air brake check, and braking on the road. Many have two numbers that look alike in the options.

  1. CDL-style question 9 · Gauges

    When must the low air pressure warning come on?

    1. AWhen pressure falls below 100 psi
    2. BWhen pressure falls below 20 psi
    3. COnly when the tanks are empty
    4. DBefore the pressure in the tanks falls below 60 psi
    Worked answer

    D: Before the pressure in the tanks falls below 60 psi. The low-air warning, a light, buzzer or wig-wag, must activate before tank pressure drops below 60 psi (or half the governor cut-out on older vehicles).

    The trap: Choosing 20 psi, which is where the spring brakes come on. The warning has to come first, before 60 psi, so you have time to stop.

  2. CDL-style question 10 · Stopping distance

    Your air brakes have a brake lag of 0.5 seconds. At 65 mph, about how far does the vehicle travel during the brake lag? (1 mph is about 1.47 feet per second.)

    1. A48 feet
    2. B95 feet
    3. C33 feet
    4. D73 feet
    Show the answer

    A: 48 feet. 65 mph × 5,280 ÷ 3,600 = 95.3 feet per second. × 0.5 s = 47.7, about 48 feet. Multiplying the mph by the seconds (32.5) forgets to change miles per hour to feet per second.

  3. CDL-style question 11 · Stopping distance

    A truck with air brakes at 55 mph has perception distance 141 feet, reaction distance 61 feet, brake lag 32 feet and braking distance 216 feet. What is its total stopping distance?

    1. A450 feet
    2. B309 feet
    3. C418 feet
    4. D389 feet
    Show the answer

    A: 450 feet. Total stopping distance is the sum of every part: 141 + 61 + 32 + 216 = 450 feet. Air brakes add brake lag to the three distances every vehicle has.

  4. CDL-style question 12 · Air brake check

    In the air brake check on a combination vehicle, with the engine off and the brake pedal held down (after the first drop), the pressure drops 5 psi in one minute. Does it pass?

    1. AYes; the limit is less than 4 psi a minute
    2. BNo; the limit is less than 2 psi a minute
    3. CYes; the limit is less than 3 psi a minute
    4. DNo; the limit is less than 4 psi a minute
    Show the answer

    D: No; the limit is less than 4 psi a minute. Applied leakage must be less than 3 psi (single) or 4 psi (combination) a minute. For a combination vehicle the limit is 4; 5 psi is over it, so it fails.

  5. CDL-style question 13 · Air brake check

    With the engine off and the brakes released, a single truck's air pressure drops 3 psi in one minute. Does it pass the static leakage test?

    1. AYes; the limit is 4 psi a minute
    2. BNo; the limit is less than 2 psi a minute
    3. CYes; the limit is less than 3 psi a minute
    4. DNo; there should be no drop at all
    Show the worked answer

    B: No; the limit is less than 2 psi a minute. Released (static) leakage must be less than 2 psi a minute for a single vehicle and less than 3 for a combination. 3 psi fails on a single truck.

    1. Released or applied? Released (brakes off).
    2. Single or combination? Single.
    3. Limit: less than 2 psi a minute. 3 psi fails.

    The trap: Using the combination or applied limit. Four numbers (2, 3, 3, 4) look alike; tie each to its condition.

  6. CDL-style question 14 · Low air

    You test the low air pressure warning by fanning the brakes with the engine off. It comes on at 50 psi. What does that mean?

    1. AIt is working correctly
    2. BIt comes on too late; it must come on before pressure falls below 60 psi
    3. CIt comes on too early; it should come on at 20 psi
    4. DThe governor is set too high
    Show the worked answer

    B: It comes on too late; it must come on before pressure falls below 60 psi. The low-air warning must activate before tank pressure falls below 60 psi. At 50 psi it is late, so it needs repair before driving.

    1. Recall the rule: the warning must come on before 60 psi.
    2. 50 psi is below 60.
    3. So the warning is late: have it fixed.

    The trap: Confusing the warning with the spring brakes (20 to 45 psi). The warning has to come well before the brakes do.

  7. CDL-style question 15 · Mountain driving

    Your safe speed on a long downgrade is 45 mph and you are in the right gear. How should you use the brakes?

    1. ALight, steady pressure all the way down
    2. BBrake firmly to 40 mph, release, and repeat when you reach 45 mph
    3. CBrake to 25 mph, then coast in neutral
    4. DFan the pedal quickly every few seconds
    Show the worked answer

    B: Brake firmly to 40 mph, release, and repeat when you reach 45 mph. Snub braking: brake hard enough to feel a definite slowdown until you are 5 mph below your safe speed, release, and repeat when you are back at the safe speed.

    1. Pick the safe speed: 45 mph.
    2. Brake until 5 mph below it: 40 mph.
    3. Release, let it climb back to 45, and repeat.

    The trap: Light, steady braking feels gentle but heats the drums continuously, which causes brake fade.

More questions like these

Eight full mocks of all three permit tests and 12 drills, every answer explained like the ones on this page.

The CDL Pass Pack gives you 8 full mocks on the real clock, 12 drills of 12 questions for the sections that cost you points, and a predictor that turns your mocks into the odds of reaching your target. One payment, no subscription, and your free score stays free.

Prep courses for these tests usually cost $19 to $129. The CDL Pass Pack is US$39 (£29), once.

See the CDL Pass Pack How our questions are built and checked
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What do CDL Combination Vehicles questions look like?

Questions on the trailer air controls and lines, coupling and uncoupling, and handling a combination: rollovers, off-tracking and which trailer goes first.

  1. CDL-style question 16 · Air system

    What happens when you pull out the red trailer air supply knob?

    1. AThe trailer brakes release
    2. BThe fifth wheel unlocks
    3. CThe tractor brakes release
    4. DThe trailer air supply shuts off and the trailer emergency brakes come on
    Worked answer

    D: The trailer air supply shuts off and the trailer emergency brakes come on. Pulling the knob out closes the tractor protection valve and applies the trailer spring brakes.

    The trap: Thinking the red knob releases the trailer brakes. Pulled out, it shuts off the trailer air, and no air means the trailer emergency brakes apply.

  2. CDL-style question 17 · Doubles

    You are coupling a set of doubles. Trailer 1 is loaded to 15,000 lb and trailer 2 to 12,000 lb. Which trailer should go directly behind the tractor?

    1. AEither one; the order does not matter
    2. BTrailer 1, because the heavier trailer goes first
    3. CTrailer 2, because the heavier trailer goes at the rear
    4. DTrailer 2, because the lighter trailer goes first
    Show the answer

    B: Trailer 1, because the heavier trailer goes first. Put the heavier trailer first, behind the tractor, and the lighter trailer at the rear. Trailer 1 is the heavier (15,000 lb).

  3. CDL-style question 18 · Following distance

    You are driving a 70-foot vehicle at 70 mph on a dry road. Using the CDL manual's rule, at least how many seconds should you keep between you and the vehicle ahead?

    1. A7 seconds
    2. B3.5 seconds
    3. C10 seconds
    4. D8 seconds
    Show the answer

    D: 8 seconds. The rule is 1 second for every 10 feet of vehicle length at speeds below 40 mph, plus 1 more second above 40 mph. 70 ÷ 10 = 7, plus 1 because you are over 40 mph = 8 seconds.

  4. CDL-style question 19 · Air system

    What happens when you pull out the red, eight-sided trailer air supply knob?

    1. AThe trailer brakes release
    2. BThe air to the trailer is shut off and the trailer emergency brakes come on
    3. CThe fifth wheel unlocks
    4. DThe tractor parking brakes release
    Show the worked answer

    B: The air to the trailer is shut off and the trailer emergency brakes come on. Pulling the red knob closes the tractor protection valve, cutting air to the trailer, so the trailer's spring (emergency) brakes apply.

    1. Red, eight-sided knob = trailer air supply.
    2. Pulled out = supply off.
    3. No supply air = trailer emergency brakes on.

    The trap: Mixing it up with the yellow diamond knob, which controls the parking brakes on the tractor (and trailer, when supplied).

  5. CDL-style question 20 · Doubles

    You are coupling doubles. Trailer 1 is loaded to 22,000 lb and trailer 2 to 14,000 lb. Which goes directly behind the tractor?

    1. ATrailer 2, because the lighter trailer goes first
    2. BTrailer 1, because the heavier trailer goes first
    3. CEither; the order does not matter
    4. DTrailer 2, so the heavy one is at the back for traction
    Show the worked answer

    B: Trailer 1, because the heavier trailer goes first. The heavier trailer goes first, behind the tractor, and the lighter one at the rear, which keeps the rear trailer from pushing and whipping.

    1. Compare the weights: 22,000 lb is heavier.
    2. Rule: heaviest trailer first.
    3. Trailer 1 goes behind the tractor.

    The trap: Thinking the heavy trailer belongs at the back "for stability". A heavy rear trailer amplifies swing in a quick lane change.

  6. CDL-style question 21 · Coupling

    After coupling, you look at the fifth wheel. Which of these shows the coupling is right?

    1. AThe jaws are closed around the head of the kingpin
    2. BThere is a small gap between the upper and lower fifth wheel
    3. CNo gap between the fifth wheels, the jaws closed around the shank of the kingpin, and the release arm locked
    4. DThe release arm is in the open position
    Show the worked answer

    C: No gap between the fifth wheels, the jaws closed around the shank of the kingpin, and the release arm locked. The upper and lower fifth wheel should touch with no gap, the jaws should close around the shank (not the head) of the kingpin, and the locking lever should be in the locked position with the safety latch over it.

    1. Look for a gap: there must be none.
    2. Check the jaws are around the shank.
    3. Check the release arm is locked and latched.

    The trap: Accepting a small gap. A gap can mean the kingpin is riding on top of the jaws (a high hitch), and the trailer can come loose.

Which facts do these questions keep coming back to?

A short list of rules with numbers. If you can say each number and the condition it belongs to, a large share of the questions on all three tests become quick wins.

The numbers the knowledge tests ask about most, with sources
RuleNumberSource
Following distance1 second per 10 feet of vehicle length below 40 mph; add 1 second above 40 mphState CDL manual
Stopping at 55 mph (dry)About 142 ft perception + 61 ft reaction + 216 ft braking = 419 ft; air brakes add about 32 ft of lagState CDL manual
Tread depthAt least 4/32 inch on front (steering) tires, 2/32 inch on all others49 CFR 393.75
Warning triangles, two-way roadWithin 10 ft of the vehicle, then about 100 ft behind and 100 ft aheadState CDL manual
Warning triangles, divided or one-way road10 ft, 100 ft and 200 ft behind, toward approaching trafficState CDL manual
Cargo checksWithin the first 50 miles, then every 3 hours or 150 miles, whichever comes firstState CDL manual
AlcoholNone within 4 hours of duty; 0.04 is DUI in a CMV; any detectable amount means 24 hours out of service49 CFR 392.5; state CDL manual
GovernorCut-out about 125 psi, cut-in about 100 psiState CDL manual, air brakes
Low-air warningMust come on before pressure falls below 60 psiState CDL manual, air brakes
Spring brakes / tractor protection valveCome on, or close, between 20 and 45 psiState CDL manual, air brakes and combinations
Air build-up (dual system)85 to 100 psi within 45 secondsState CDL manual, air brakes
Leakage, engine offReleased: under 2 psi a minute (single), 3 (combination). Applied: under 3 (single), 4 (combination)State CDL manual, air brakes
Slack adjuster free playNo more than about 1 inch when pulled by handState CDL manual, air brakes

Notice how many of the wrong options above are real numbers from a neighboring rule: 20 psi where 60 psi belongs, the 10-100-200 pattern where the two-way pattern belongs, 2/32 inch where a steering tire needs 4/32. That is how the real tests are built too, so learn each number together with its condition.

How should I use CDL sample questions?

Answer each before you open the working, write down the rule behind every miss, and then take a full timed practice test to check the rules have stuck.

A sample set is small, so a good score here proves little. A wrong answer, though, points straight at a rule you can learn in a minute: which line is red, what the yellow diamond knob does, when the low-air warning must come on. Write each one on a card.

Then take the free CDL practice test, which has 95 questions across all three tests and scores each against 80%, or a free drill on the General Knowledge, Air Brakes or Combination page, where every answer is explained.

Your state CDL manual is the final word. Where a question here and your manual seem to disagree, follow the manual and tell us, because states occasionally word a rule differently.

Are these like the real CDL test questions?

They follow the content of the standard state CDL manual and the federal rules, in the same four-option style, but they are original and none is a real DMV question.

States do not publish their knowledge-test questions, and copies that circulate online are often out of date or wrong. Every question here was written from the manual and checked by an independent re-solve that saw only the question and the options. The CDL test guide explains how the real tests are given, and CDL passing score explains the 80% rule.

The real tests differ in one way you should practise for: they are scored test by test, so a sample set that mixes all three is no substitute for checking each test on its own. That is what the drills and the full practice test do.

Frequently asked questions

Are these real CDL test questions?

No. They are original CDL-style questions written for LifeScore from the state CDL manual and the federal rules. States do not publish their own test questions.

Where can I get the official CDL manual?

Free from your state licensing agency's website. Every state's manual follows the same national model.

How many questions are on each real test?

Washington lists 50 General Knowledge, 25 Air Brakes and 20 Combination Vehicles questions. Some states ask 20 Air Brakes or 25 Combination questions.

Do these questions appear in your mocks?

No. This sample set is kept out of every mock and drill, so practising here never spoils a full test.

Ready for a full test?

Eight full CDL-style mocks, 12 drills and every answer explained, for one payment.

The CDL Pass Pack gives you 8 full mocks on the real clock, 12 drills of 12 questions for the sections that cost you points, and a predictor that turns your mocks into the odds of reaching your target. One payment, no subscription, and your free score stays free.

Prep courses for these tests usually cost $19 to $129. The CDL Pass Pack is US$39 (£29), once.

See what is inside the CDL Pass Pack How our questions are built and checked
8
timed mocks
12
topic drills
1
score predictor

LifeScore is not affiliated with, endorsed by or connected to the Federal Motor Carrier Safety Administration (FMCSA), AAMVA or any state licensing agency or DMV. Test and agency names belong to their owners. Our CDL-style practice tests use original questions written for this site from the federal rules and the standard state CDL manual; they are not the official tests, and your state manual is the final word.

Facts last checked by the LifeScore Editorial Team. How we check facts.