CDL knowledge test

Find out how to prepare for and take the Commercial Driver License (CDL) knowledge test.

The knowledge test is available in 4 languages:

  • English
  • Spanish
  • Russian
  • Serbian–Croatian

Note: language interpreters aren't allowed.

Taking the knowledge test

Make an appointment to take the knowledge test at a driver licensing office location that offers testing. The test fee covers one attempt at each knowledge test taken within 90 days of the receipt. See Getting a CDL for the list of required documents you'll need to bring with you.

You must pass the knowledge test to get a Commercial Learner's Permit (CLP).

You must take the knowledge test:

  • Before you can take the skills test.
  • Any time you upgrade your CDL by moving to a higher commercial class or adding endorsements that require a skills test.

Endorsements include:

  • Passenger endorsement
  • School bus endorsement
  • Tank vehicle endorsement (only if testing and or training in tank vehicle)
  • Removing an air brake restriction

You're required to take the knowledge test any time you:

Knowledge test scores are valid for:

  • 180 days from the date passed.
  • Another 180 days, if you renew your CLP within 30 days of your original CLP expiring. Double, triple, and hazardous materials cannot be renewed with CLP and expire 180 days from the date passed.

Penalties for trying to get a CDL fraudulently could include:

  • Cancellation of your driver license.
  • Having to wait up to 1 year before you can apply again for a CDL.

Types of CDL knowledge tests

Knowledge test Total questions Passing score Skills test needed
CDL general knowledge (A, B, & C) 50 40 Yes
CDL combination (A) 20 16 Yes
Passenger 20 16 Yes
Air brakes 25 20 Yes
School bus 20 16 Yes
Double/triple 20 16 No
Tank vehicle 20 16 No*
Hazardous materials 30 24 No

*Unless you're taking your skills test or training in a commercial tank vehicle. Then you must take the knowledge test before we can issue your CLP.

Need additional help? Here's how to contact us:

call Phone: 360-902-3900
(TTY: Call 711)
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