General Knowledge (Class A) Study Guide
The General Knowledge test is the cornerstone of the CDL written exam. Every Class A applicant takes it, and it's the longest single section you'll see — typically about 50 multiple-choice questions covering the core skills any commercial driver needs regardless of what they're hauling. The good news: there's no trick to this test. It rewards drivers who actually understand the material instead of trying to memorize answers.
What's actually on the test
The General Knowledge section pulls from five broad areas: vehicle inspection, basic vehicle control, safe driving practices, transporting cargo, and emergencies. You won't see every topic equally weighted on every test, but expect a heavy emphasis on inspection and safe driving — those two together usually make up half the questions.
Vehicle inspection
Pre-trip inspection isn't just for the skills test — it's tested on the written exam too. Know the seven steps of an air brake test, what a leaking power steering hose looks like, why slack adjusters matter, and how to identify worn tires. A common question: how much tread depth do steering tires need? (Answer: at least 4/32 of an inch on every major groove.) For all other tires, the minimum is 2/32.
Basic vehicle control
Backing, turning, and managing space around your vehicle. Pay attention to off-tracking — when you turn, the rear wheels follow a tighter path than the front wheels. The longer your vehicle, the more pronounced this is. On right turns especially, you'll need to swing wider to keep the trailer from cutting the corner. Don't confuse yourself by swinging into the left lane first to make the right turn — that's a common mistake that leads to a sideswipe.
Safe driving practices
Stopping distance, following distance, hazard awareness. The standard rule: one second of following distance for every 10 feet of vehicle length, at speeds under 40 mph. Add one more second above 40 mph. So a 60-foot tractor-trailer at 50 mph needs at least seven seconds of following distance. Stopping distance breaks into three parts: perception distance, reaction distance, and braking distance. Adverse conditions — rain, snow, ice — increase all three. On wet roads, you should at least double your following distance.
Transporting cargo
Weight distribution, securement, and rules of thumb for high-center-of-gravity loads. Cargo must be inspected within the first 50 miles of a trip, then at least every 150 miles or every three hours of driving (whichever comes first), and again every time you take a break or change duty status. Overloaded vehicles handle worse, take longer to stop, and put you at legal risk at every weigh station.
Emergencies
Fire, brake failure, blowouts, skids. Know which type of fire extinguisher works on which type of fire (a B:C or A:B:C rated extinguisher for most cab fires). Know that you should never use water on an electrical, gas, or oil fire. For a tire blowout, hold the steering wheel firmly, stay off the brake, and let the vehicle slow on its own before pulling over.
The trap most people fall into
The biggest mistake on the General Knowledge test is assuming the "right answer" is the one that sounds the safest. Some questions are written specifically to test whether you know the actual rule, not your gut feeling. For example: "When approaching a railroad crossing, you should always come to a complete stop." That's wrong for most CDL drivers — only certain vehicles (placarded HAZMAT, school buses, passenger buses) are required to stop at every public crossing. A regular tractor-trailer driver should slow, look both ways, and proceed if clear, unless required to stop by signs or signals.
Read every question carefully. The wrong-but-tempting answers usually come from oversimplifying the rule.
How to study efficiently
Take the practice test below. Don't grind a single attempt — take the test, see your score, read every explanation, then take it again. Each retake pulls a different randomized set of questions, so you're not memorizing answers, you're learning rules. When you can hit 90%+ on three consecutive attempts, you're ready for the DMV.
If you find yourself missing the same type of question over and over (say, brake-related ones), spend 20 minutes reading the relevant section of your state's CDL Manual before retaking. The state manual is free, and our questions are modeled from the same FMCSA source material it uses.
What's next after passing
Passing General Knowledge is the foundation. From there, you'll also need Air Brakes (if your vehicle has them — almost all commercial trucks do) and Combination Vehicles (for any Class A). Add endorsements as needed: HAZMAT, Tanker, Doubles/Triples for over-the-road work; Passenger and School Bus for those specific careers.
Once your written tests are done, you'll receive a Commercial Learner's Permit (CLP). You must hold it for at least 14 days, complete FMCSA-required ELDT theory training, and then take the skills test. Find a CDL school near you on CDLSpot if you haven't picked one yet.