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CDL practice test

Every question is written from the General Knowledge sections of the official Commercial Driver's License Manual (Classes A, B and C), and every answer shows the section it comes from, so you can check it yourself.

Practice test: 50 questions. The real test needs 80% to pass. Federal rules require at least 80 percent on every CDL knowledge test. Many states give 50 General Knowledge questions (40 right to pass), but the count varies by state and license class, so check with yours. Test format source

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Sample questions

If your speed goes from 20 to 40 mph, what happens to your braking distance?

  1. It stays about the same
  2. It doubles
  3. It becomes 4 times longer
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It becomes 4 times longer. Braking distance grows much faster than speed. Going from 20 to 40 mph makes it 4 times longer, and impact force rises the same way.

From the manual: Section 2 Driving Safely, 2.6.1 Stopping Distance (manual p. 2-14, PDF p. 32)

You have to stop on the shoulder of a road. How soon must your emergency warning devices be set out?

  1. Within 10 minutes
  2. Within 30 minutes
  3. Within 60 minutes
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Within 10 minutes. Turn on your four-way flashers right away and set out your warning devices within 10 minutes.

From the manual: Section 2 Driving Safely, 2.5.2 Communicating Your Presence (manual p. 2-12, PDF p. 30)

At what blood alcohol concentration (BAC) is it illegal to drive a CMV?

  1. 0.04% or more
  2. 0.08% or more
  3. 0.10% or more
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0.04% or more. For CMV drivers the limit is 0.04%. If you drive a CMV, you are considered to have consented to alcohol testing.

From the manual: Section 1 Introduction, 1.3.1 General (disqualifications) (manual p. 1-7, PDF p. 13)

What are the minimum tread depths for your tires?

  1. 4/32 inch on front tires and 2/32 inch on the others
  2. 4/32 inch on every tire
  3. 2/32 inch on front tires and 4/32 inch on the others
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4/32 inch on front tires and 2/32 inch on the others. Front tires need at least 4/32 inch of tread in every major groove, and all other tires need at least 2/32 inch. No fabric should show through.

From the manual: Section 2 Driving Safely, 2.1.3 What to Look For (manual p. 2-1, PDF p. 19)

Your vehicle must stop at a railroad crossing that has no white stop line. Where do you stop?

  1. Between 5 and 10 feet from the nearest rail
  2. Between 15 and 50 feet from the nearest rail
  3. Between 50 and 100 feet from the nearest rail
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Between 15 and 50 feet from the nearest rail. Without a stop line, vehicles that must stop do so at least 15 feet, and no more than 50 feet, from the nearest rail.

From the manual: Section 2 Driving Safely, 2.15.2 Warning Signs and Devices (manual p. 2-31, PDF p. 49)

How should you load cargo to keep the center of gravity low?

  1. Put the heaviest parts by the rear doors
  2. Put the heaviest parts on top
  3. Put the heaviest parts under the lightest parts
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Put the heaviest parts under the lightest parts. A high center of gravity makes a rollover more likely, especially in curves or when you swerve. Keep the load as low as possible.

From the manual: Section 3 Transporting Cargo Safely, 3.2.3 Don't Be Top-heavy (manual p. 3-2, PDF p. 65)

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