Take a free practice quiz or point your phone at any CDL general knowledge question for an instant, explained answer — air brakes, vehicle inspection, and federal rules, without the guesswork.
Try it freePoint your phone at the question — on a screen, a printout, anywhere.
Cambo reads the question and answers it in a few seconds.
Read the reasoning behind the answer so it actually sticks.
Looking for the official training, not practice questions? fmcsa.dot.gov — Federal Motor Carrier Safety Administration ↗
Taking it right now? Snap a photo of any question you get stuck on — get the answer in seconds.
Try it freeThe General Knowledge test is built on federal FMCSA regulations (49 CFR Part 383) that nearly every state's written CDL permit exam draws from, but the material covers a lot of narrow, specific rules — pre-trip inspection steps, air brake system components, hours-of-service limits — that are easy to mix up under pressure. Cambo reads the exact question and explains the specific federal rule or safe-driving principle behind the correct answer.
Federal rules set a minimum of 30 questions, but most states use a longer General Knowledge test form, commonly 50 questions.
80% — federal regulation (49 CFR 383.135) requires every state to set this same passing threshold on each CDL knowledge test.
It depends on the class of CDL and any endorsements you're pursuing. Everyone takes General Knowledge; driving a vehicle with air brakes requires the Air Brakes test, combination vehicles (like a tractor-trailer) require the Combination Vehicles test, and endorsements like Hazmat, Passenger, School Bus, or Tanker each have their own additional test.
Most states allow multiple attempts, but a mandatory waiting period between attempts (commonly a few days to a week) and any cap on total tries before reapplying vary by state — check your state's DMV or licensing agency for exact rules.
No. Cambo is an independent study tool, not produced or endorsed by the Federal Motor Carrier Safety Administration or any state motor vehicle agency.
Requirements vary by state, but generally include holding a valid regular driver's license, meeting minimum age requirements (18 for intrastate driving, 21 for interstate or hazmat), and passing a DOT medical exam to hold a valid medical certificate.