CDL guide
CDL endorsements, without the jargon pile-up.
Commercial licensing stacks a general-knowledge foundation with endorsement tests for the equipment and cargo you will actually haul.
Start with general knowledge
Most CDL paths begin with general knowledge: inspections, space and speed management, communication, hazards, and safe operation. Endorsements build on that base. If general knowledge is shaky, endorsement practice usually feels scattered.
Knowledge tests are federally regulated: you must correctly answer at least 80% of the questions on each knowledge test (49 CFR 383.135(a)(1)). States set the question count; the pass mark does not change.
What each endorsement is about
- General knowledge
The foundation for commercial driving: inspections, space, speed, communication, hazards, and safe operation.
- Air brakes
Understand air-brake components, inspections, warning devices, stopping distance, and controlled braking.
- Combination vehicles
Prepare for safe coupling, inspection, turning, backing, and handling of tractor-trailer combinations.
- Hazardous materials (H)
Study hazard communication, shipping papers, placards, loading rules, parking, and emergency response responsibilities.
- Tank vehicles (N)
Learn how liquid surge, outage, bulkheads, and high centers of gravity change vehicle handling.
- Doubles & triples (T)
Practice converter-dolly inspection, coupling order, rearward amplification, and stability principles.
- Passenger vehicles (P)
Prepare to inspect, load, and operate buses while keeping passengers, aisles, and exits safe.
- School bus (S)
Review student loading, danger zones, mirrors, emergency procedures, and special railroad-crossing duties.
How to practice without over-promising
Use practice to find weak topics early, then verify current state requirements with the official agency linked from each QuizLane CDL hub. Training providers, medical cards, and skills tests are separate from the knowledge checks QuizLane covers. Entry-Level Driver Training has been mandatory since February 7, 2022 (49 CFR 380.600) for new Class A/B credentials and first passenger, school bus, or hazmat endorsements.
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Prefer browsing first? Open the CDL directory · General knowledge practice test.