The CDL (Commercial Driver's License) knowledge test is more demanding than the standard DMV test. It covers a broader range of topics, has more questions, and requires a higher level of understanding. Here's what to expect.
Test format
- Questions: 50 multiple-choice questions (general knowledge)
- Passing score: 80% in most states (40 out of 50)
- Endorsement tests: Additional 20-30 questions per endorsement
- Format: Computer-based at most DMV/DPS offices
What the CDL test covers
The general knowledge test covers topics that apply to all commercial vehicles regardless of class:
- Vehicle inspection procedures (pre-trip, en-route, post-trip)
- Basic vehicle control and safe driving
- Transporting cargo safely
- Air brakes (if your vehicle has them)
- Combination vehicles (for Class A)
- Hours of service regulations
- Hazardous materials basics
ELDT requirement: Since February 2022, you must complete Entry-Level Driver Training (ELDT) through an FMCSA-registered training provider before taking the CDL skills test. This applies to Class A, Class B, and certain endorsements. Learn more about CDL endorsements.
How to prepare
Step 1: Read the CDL handbook for your state. It's longer than the regular driver handbook but every test question comes from it.
Step 2: Take practice tests by topic. Start with general knowledge, then work through each endorsement you need. DMV IQ has free CDL practice tests covering all topics and endorsements.
Step 3: Focus on air brakes. The air brake section has the most specific technical details and trips up many test-takers.
CDL classes explained
- Class A: Combination vehicles over 26,001 lbs GVWR when towed unit exceeds 10,000 lbs (tractor-trailers)
- Class B: Single vehicles over 26,001 lbs (buses, dump trucks, large straight trucks)
- Class C: Vehicles for 16+ passengers or carrying hazardous materials, not meeting Class A/B thresholds
