CDL Class B Permit Practice Test: Free Questions and Answers
A Class B CDL covers any single vehicle rated 26,001 pounds GVWR or more (straight trucks, dump trucks, large buses), including that vehicle towing a trailer of 10,000 pounds GVWR or less. The permit knowledge test is the same general knowledge exam every CDL applicant takes, plus a separate air brakes section if your vehicle has them. Below are 10 original practice questions with explained answers, built from official state CDL manual content.
State motor vehicle agencies administer the test, so the exact question count and how the manual sections are organized differ by state, even though the passing score is set federally at 80 percent for every knowledge test section. Pennsylvania and California both structure their CDL manuals on the same AAMVA model curriculum, and the numbers below are checked against both.
What is a Class B CDL and what can you drive with it?
A Class B license lets you drive any single commercial vehicle with a gross vehicle weight rating (GVWR) of 26,001 pounds or more, including box trucks, dump trucks, city transit buses, and most school buses, plus that same vehicle towing a trailer up to 10,000 pounds GVWR (PennDOT Commercial Driver’s License Fact Sheet, June 2025). Tow anything heavier than that behind it, once the combined weight hits 26,001 pounds and the trailer alone tops 10,000 pounds, and you need a Class A license instead. A Class B license also covers everything a Class C license does, since B is the broader class.
What’s on the Class B permit knowledge test?
Every CDL applicant, regardless of class, takes the general knowledge test first. It covers vehicle inspection, basic control, safe driving practices, cargo securement, and the traffic laws that apply to commercial vehicles, drawn from the same core content federal rule 49 CFR Part 383 requires every state to test. Class B applicants skip the combination vehicles test, since that section is a Class A only requirement, but they still take separate tests for any endorsement they add, such as passenger (P) or school bus (S).
Does the Class B test include air brakes questions?
Only if you plan to drive, or test in, a vehicle equipped with air brakes. Skip the air brakes knowledge test, or score under 80 percent on it, and the state issues your CDL with an “L” restriction that blocks you from operating any air brake equipped commercial vehicle, under 49 CFR 383.135(a)(2). Most Class B straight trucks and buses over roughly 33,000 pounds run air brakes, so in practice most Class B applicants end up studying and testing on that section anyway. We built two of the ten questions below around it for that reason.
How many questions are on the test, and what’s the passing score?
Pennsylvania’s Class B knowledge test runs 50 questions, and PennDOT requires 80 percent correct, 40 of 50, to pass (PennDOT Commercial Driver’s License Fact Sheet, June 2025). California’s Commercial Driver Handbook covers the same core material for its Class B general knowledge test. Every state has to hold applicants to that same 80 percent floor on each knowledge test section under 49 CFR 383.135(a)(1), even though the exact question count on the general knowledge section runs from about 40 to 50 depending on the state. Check your own state DMV or DPS page for the exact number before test day.
Class B permit test at a glance
| Test element | What applies |
|---|---|
| Vehicle covered | Single vehicle, 26,001+ lbs GVWR, or towing 10,000 lbs GVWR or less |
| Knowledge test required | General knowledge (all CDL classes) |
| Air brakes test | Required only if the vehicle has air brakes; otherwise an “L” restriction applies |
| Combination vehicles test | Not required for Class B (Class A only) |
| Passing score | 80 percent on every section, set by federal rule |
| Question count | 50 in Pennsylvania; most states run 40 to 50 |
| Permit validity | Up to one year from issuance |
10 original Class B practice questions
These are original questions we wrote to match the topics official state manuals cover. They are not copied from any exam or third party question bank.
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During a pre-trip inspection you find a tire with a visible bulge in the sidewall. What should you do? Answer: Do not drive the vehicle until the tire is replaced. A sidewall bulge means the internal cords are damaged, and the tire can blow out under load or heat. Treat any damaged tire as an out-of-service condition, not something to monitor.
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You check your air gauge before driving and the needle climbs slower than usual while the engine idles. What does this suggest? Answer: A possible air compressor or line problem. Air pressure should build from about 50 to 90 psi within three minutes on a low-idle engine. A slow climb means the system needs a mechanic’s look before the vehicle goes out.
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You’re backing a straight truck toward a loading dock and lose sight of the rear of the vehicle in your mirrors. What should you do? Answer: Stop and get out to check your path before continuing. This is the “get out and look” rule: never guess your clearance from the cab, and reposition a spotter or re-check on foot every time you lose the visual.
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At speeds under 40 mph, roughly how much following distance should you keep behind the vehicle ahead in a loaded straight truck? Answer: About one second for every 10 feet of your vehicle’s length, with at least 4 seconds total, and one more second added once you’re over 40 mph. A heavier vehicle needs more room to stop than a car does, even well under the speed limit.
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Your straight truck starts to hydroplane on a wet road. What is the correct response? Answer: Ease off the accelerator and avoid braking or turning sharply until the tires regain contact with the road. Hard braking or a sudden steering input on hydroplaning tires is what actually causes the vehicle to skid or roll.
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You’re approaching a green light at an intersection with cross traffic visible. What should you do? Answer: Cover the brake and be ready to stop, since a green light does not guarantee cross traffic will stop. Commercial vehicles need more stopping distance than passenger cars, so entering an intersection at full speed on a stale green is a common cause of preventable crashes.
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What does a low air pressure warning light or buzzer in an air brake equipped Class B vehicle mean? Answer: Air pressure has dropped below approximately 60 psi, and the vehicle should be stopped safely as soon as possible. Continuing to drive on falling air pressure risks the spring brakes locking up automatically at a lower threshold, which can happen mid-maneuver.
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What is the purpose of spring brakes on an air brake equipped truck? Answer: They apply automatically as an emergency and parking brake if air pressure drops too low to hold the service brakes. Springs, not air pressure, physically hold the brakes on; air pressure is what releases them, which is why a total air loss still stops the vehicle.
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You’ve been driving for several hours and start to feel drowsy. What is the safest response? Answer: Pull off at the next safe location and rest, rather than trying to push through with the radio or a window down. Fatigue slows reaction time in ways a driver often cannot feel happening in the moment.
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You approach a railroad crossing with a low ground clearance warning sign. What should you check before crossing? Answer: Whether your vehicle’s underside clearance is enough to cross without the frame or trailer catching on the raised tracks. Long wheelbase straight trucks and low step vans are the vehicles most likely to get stuck on a raised crossing, and getting stuck there is a leading cause of truck versus train collisions.
Ready to practice more
Run through a full-length timed set in the CDL Practice Hub practice quiz tool to see where you stand before test day, and pair it with the CDL Practice Hub Class B study guide for section-by-section review.
FAQ
Is the Class B general knowledge test different from the Class A test? No. Every CDL applicant, Class A, B, or C, takes the same general knowledge test covering vehicle inspection, basic control, and safe driving. Class A applicants add the combination vehicles test on top of it; Class B applicants do not take that section at all.
Do I need the air brakes test for a Class B permit? Only if the vehicle you’ll drive or test in has air brakes. Skip it or fail it and your CDL comes with an “L” restriction barring you from air brake equipped vehicles, which covers most full-size straight trucks and buses.
How long is a Class B CDL permit valid? Up to one year from the date it’s issued, under federal rule 49 CFR 383.25. Some states issue permits for a shorter initial period and allow a renewal within that same one-year window without retesting.
Can I drive a Class A vehicle with a Class B license? No. A Class B license only covers single vehicles and light towed trailers under 10,000 pounds GVWR. Driving a heavier combination requires passing the separate combination vehicles knowledge and skills tests for Class A.
How many times can I retake the Class B knowledge test if I fail? Retake limits and any waiting period between attempts are set by your state, not federal rule, so they vary. Most states allow multiple retakes but may charge a retest fee after the first one or two attempts.