CDL General Knowledge Practice Test 2026: Practice test 4

1. Question 1 of 25

   When should you check your mirrors during a lane change?

   • AOnly once, after you finish the lane change
   • BOnly once, just before you turn on your signal
   • COnly if another driver honks or flashes lights
   • DBefore, after signaling, as you start and after
   Show answer

   Answer: D. Before, after signaling, as you start and after

   Check mirrors at each stage of a lane change to be sure no one is in the space you are moving into.

2. Question 2 of 25

   This diagram shows the blind spots around a large truck. Why should you avoid driving alongside other vehicles for long periods?

   • AA driver may change lanes into you, or you may get boxed in
   • BIt wastes fuel because of the extra wind resistance
   • CIt is illegal on all highways in the United States
   • DOther drivers can see you too clearly and slow down
   Show answer

   Answer: A. A driver may change lanes into you, or you may get boxed in

   Traveling next to others is risky: they may not see you and turn into you, and they block your escape route.

3. Question 3 of 25

   The diagram shows blind spots around a truck. A car you saw in your right mirror is no longer visible. What should you assume?

   • AIt may still be beside you, hidden
   • BIt has dropped far behind your truck
   • CIt has turned off onto a side road
   • DIt has already passed you on the right
   Show answer

   Answer: A. It may still be beside you, hidden

   Mirrors do not show everything. Assume a vehicle may be in a blind spot until you are sure it is not.

4. Question 4 of 25

   This diagram shows the blind spots around a truck. What is the best way to cover them before a lane change?

   • ARely on other drivers to stay clear of you
   • BChange lanes quickly so no one gets in
   • CSound the horn and change lanes right away
   • DSignal early and check mirrors as you move
   Show answer

   Answer: D. Signal early and check mirrors as you move

   Signal early, change lanes slowly and smoothly, and check your mirrors before, during and after the move.

5. Question 5 of 25

   When should you turn on your turn signal?

   • AOnly if there are cars behind you
   • BWell before the turn, until it is done
   • CJust as you start to turn the wheel
   • DAfter you have finished the turn
   Show answer

   Answer: B. Well before the turn, until it is done

   Signal early and continuously, and cancel the signal after the turn is complete.

6. Question 6 of 25

   A driver behind you wants to pass. Should you wave them on when you think it is safe?

   • AYes, always wave them past
   • BNo, do not direct traffic
   • CYes, by turning on your right signal
   • DYes, but only at night
   Show answer

   Answer: B. No, do not direct traffic

   Do not signal others that it is safe to pass. You could cause a crash and be blamed.

7. Question 7 of 25

   How can you warn drivers behind you that you are slowing down?

   • ASwitch your headlights to high beam
   • BWave your arm out of the window
   • CSound the horn several times quickly
   • DTap the brake pedal to flash the brake lights
   Show answer

   Answer: D. Tap the brake pedal to flash the brake lights

   A few light taps on the brake pedal flash the brake lights and warn drivers behind you.

8. Question 8 of 25

   You stop on the road or shoulder. How soon must you put out your warning devices?

   • AWithin 1 hour
   • BWithin 30 minutes
   • COnly if it is dark
   • DWithin 10 minutes
   Show answer

   Answer: D. Within 10 minutes

   Turn on the four-way flashers and set out warning devices as soon as possible, within 10 minutes.

9. Question 9 of 25

   You stop on a two-lane road with traffic going both ways. Where should you place your three triangles?

   • A10 feet ahead, 10 feet behind and one on the roof
   • BAll three within 10 feet of the front bumper
   • C10 feet from the vehicle, 100 feet behind and 100 feet ahead
   • D50 feet behind, 100 feet behind and 150 feet behind
   Show answer

   Answer: C. 10 feet from the vehicle, 100 feet behind and 100 feet ahead

   On a two-way road, place one triangle within 10 feet of the vehicle and one about 100 feet behind and ahead.

10. Question 10 of 25

    You stop on a one-way road or divided highway. Where should you place your triangles?

    • A10 feet ahead, 100 feet behind and 100 feet ahead
    • BOnly one triangle, 50 feet behind
    • C500 feet behind the vehicle
    • D10 feet, 100 feet and 200 feet toward approaching traffic
    Show answer

    Answer: D. 10 feet, 100 feet and 200 feet toward approaching traffic

    On a one-way or divided highway, place them 10, 100 and 200 feet back toward approaching traffic.

11. Question 11 of 25

    You stop just past a hill or curve that blocks the view of drivers behind. What should you do with the rear triangle?

    • APlace it in front of your vehicle instead of behind
    • BMove it back so drivers see it before the hill or curve
    • CLeave all three triangles within 10 feet of the truck
    • DDo not use triangles, because no one can see them
    Show answer

    Answer: B. Move it back so drivers see it before the hill or curve

    If a hill or curve within 500 feet blocks the view, move the rear-most triangle back so drivers get enough warning.

12. Question 12 of 25

    Total stopping distance is made up of which three parts?

    • ASight distance, skid distance and gear distance
    • BPerception distance, reaction distance and braking distance
    • CFollowing distance, braking distance and coasting distance
    • DMirror distance, signal distance and stopping distance
    Show answer

    Answer: B. Perception distance, reaction distance and braking distance

    Total stopping distance is the distance you travel while you see the hazard, react, and brake to a stop.

13. Question 13 of 25

    At 55 mph, about how far does a truck travel during an average perception time of 1¾ seconds?

    • AAbout 61 feet
    • BAbout 400 feet
    • CAbout 142 feet
    • DAbout 20 feet
    Show answer

    Answer: C. About 142 feet

    At 55 mph, the average perception time of 1¾ seconds covers about 142 feet.

14. Question 14 of 25

    On dry pavement with good brakes, what is the minimum total stopping distance for a heavy vehicle at 55 mph?

    • AAbout 142 feet
    • BAbout 419 feet
    • CAbout 1,000 feet
    • DAbout 216 feet
    Show answer

    Answer: B. About 419 feet

    Perception (142 ft), reaction (61 ft) and braking (216 ft) add up to about 419 feet, longer than a football field.

15. Question 15 of 25

    You double your speed from 20 to 40 mph. What happens to your braking distance and impact?

    • AThey double
    • BThey become about four times greater
    • CThey stay the same
    • DThey become about ten times greater
    Show answer

    Answer: B. They become about four times greater

    Whenever you double your speed, braking distance and the force of a crash are about four times greater.

16. Question 16 of 25

    Why do empty trucks often need more distance to stop than loaded trucks?

    • ATheir brakes are weaker
    • BThey have less traction
    • CThey are always driven faster
    • DTheir engines are smaller
    Show answer

    Answer: B. They have less traction

    An empty truck has less weight on its tires, so it has less traction and can take longer to stop.

17. Question 17 of 25

    On a wet road, how much should you reduce your speed?

    • ANot at all, if your tires are good
    • BBy about one-third (55 to about 35 mph)
    • CBy about 5 mph (55 to about 50 mph)
    • DBy about two-thirds (55 to about 20 mph)
    Show answer

    Answer: B. By about one-third (55 to about 35 mph)

    Wet roads can double stopping distance, so slow down by about one-third.

18. Question 18 of 25

    How slow can a vehicle be going and still hydroplane if there is a lot of water?

    • AOnly above 55 mph
    • BOnly on ice
    • CAs low as 30 mph
    • DOnly above 65 mph
    Show answer

    Answer: C. As low as 30 mph

    Hydroplaning can happen at speeds as low as 30 mph when there is a lot of water.

19. Question 19 of 25

    Your vehicle starts to hydroplane. What should you do?

    • ASpeed up to get through the water
    • BBrake hard until the tires grip
    • CRelease the accelerator and push in the clutch
    • DTurn the wheel sharply to the side
    Show answer

    Answer: C. Release the accelerator and push in the clutch

    To regain control, let the vehicle slow down: release the accelerator and push in the clutch. Do not brake.

20. Question 20 of 25

    When should you watch for black ice?

    • AWhen it is below freezing and the road looks wet
    • BOnly on gravel roads in the country
    • COnly in the afternoon on sunny days
    • DOnly while snow is falling heavily
    Show answer

    Answer: A. When it is below freezing and the road looks wet

    Black ice is a thin layer that looks like a wet road. Watch for it when temperatures are below freezing.

21. Question 21 of 25

    What is the right way to handle a curve?

    • ABrake hard in the middle of the curve
    • BShift to neutral in the curve
    • CSpeed up as you enter the curve
    • DSlow down before it; don't brake in it
    Show answer

    Answer: D. Slow down before it; don't brake in it

    Slow down before you enter a curve. Braking in a curve can lock the wheels and cause a skid.

22. Question 22 of 25

    At night, how fast should you drive?

    • ASlow enough to stop within what you can see
    • BAt the posted limit, no matter what
    • CAs fast as the vehicle ahead of you
    • DFaster, because traffic is lighter
    Show answer

    Answer: A. Slow enough to stop within what you can see

    You must be able to stop within the distance you can see ahead. Low beams show less, so slow down.

23. Question 23 of 25

    What is the number one cause of injury and death in work zones?

    • APotholes
    • BBad weather
    • CConstruction equipment
    • DSpeeding traffic
    Show answer

    Answer: D. Speeding traffic

    Speeding traffic is the leading cause of injury and death in work zones, so slow down.

24. Question 24 of 25

    Going down a long, steep grade, what should be the main way you control your speed?

    • AThe parking brake, pulled on a little
    • BThe service brakes, held down all the way
    • CNeutral, so the vehicle can coast freely
    • DEngine braking in a low gear chosen before the grade
    Show answer

    Answer: D. Engine braking in a low gear chosen before the grade

    Use a low gear selected before you start down, and let the engine do most of the braking.

25. Question 25 of 25

    Your safe speed on a downgrade is 40 mph. You are in the right low gear. How should you use the brakes?

    • APump the brakes quickly the whole way down
    • BBrake to about 35 mph, release, and repeat at 40
    • CWait until you reach 60 mph, then brake hard
    • DHold the brakes on lightly all the way down
    Show answer

    Answer: B. Brake to about 35 mph, release, and repeat at 40

    Brake just enough to feel a slowdown until you are about 5 mph below safe speed, then release. Each application lasts about 3 seconds.

Keyboard: 1–4 to answer, Enter for the next question.

The real test: Varies by state; usually 50 questions, with 40 correct needed (80%)