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CDL Study Guides · 2026
Plain-English guides to every part of the CDL knowledge test — written from the FMCSA standards each state's exam is built on, with the real numbers you're actually tested on. Read a section, then practice it.
Last reviewed 2026-06-20 · Free · See our sources & methodology.
Required for every CDL class (A, B, and C).
General Knowledge is the one section every CDL applicant must pass, no matter which class or endorsement you're after. Get this right and most of the rest of the test gets easier.
Required to remove the air-brake (L) restriction from your CDL.
If your vehicle has air brakes, you have to pass this section — or you'll get an 'L' restriction stamped on your license that bars you from driving air-brake-equipped trucks.
Required for a Class A CDL (tractor-trailer combinations).
Pulling a trailer changes how the whole vehicle behaves. This section is required for a Class A CDL and covers the coupling and handling skills that keep a tractor-trailer together and under control.
Required for the HazMat (H) endorsement — plus a TSA security threat assessment.
The HazMat endorsement opens up higher-paying loads — but it's also the only endorsement that requires a federal TSA background check on top of passing the knowledge test.
Required for the Tank Vehicle (N) endorsement.
A tank full of moving liquid is one of the hardest loads to drive. This section is required for the tank (N) endorsement and centers on the one thing that catches new tanker drivers off guard: surge.
Required for the Doubles/Triples (T) endorsement.
Pulling two or three trailers multiplies both the paperwork and the physics. This section is required for the doubles/triples (T) endorsement and focuses on the rearward amplification that makes these rigs flip.
Required for the Passenger (P) endorsement.
Carrying people raises the stakes on every decision. This section is required for the passenger (P) endorsement and covers the extra inspection, boarding, and emergency rules that come with a busload of riders.
Required for the School Bus (S) endorsement (in addition to the passenger endorsement).
No CDL job carries more responsibility than driving children. The school bus (S) endorsement adds rules built around the most dangerous moments of the route: when students are getting on and off.
Tested in the CDL skills test and required by federal law before every trip.
The pre-trip inspection is both a federal requirement before every shift and one of the first things you're graded on during the CDL skills test. Knowing it cold protects your license and your load.
The CDL knowledge test isn't one exam — it's a set of sections. Everyone takes General Knowledge. From there, the sections you need depend on the class of license and the endorsements you want: Air Brakes to drive an air-brake truck, HazMat for placarded loads, Passenger and School Bus for buses, and so on. Each section requires 80% to pass.
These guides cover the knowledge sections. The fees and timeline vary by state — see how much a CDL costs in your state and your state's specific rules.
Study a section, then run the practice questions until you're past the 80% bar.
See also CDL costs by state · Sources & methodology · About Koydo CDL
Based on the FMCSA CDL Manual, a U.S. federal government publication in the public domain. Independent study aid — not affiliated with or endorsed by FMCSA, AAMVA, or any state DMV. Always confirm current rules with your state DMV.