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In the United States, there are three main classes of Commercial Driver’s Licenses (CDLs). A Class A CDL allows you to operate a combination vehicle with a gross combination weight rating (GCWR) of 26,001 pounds or more, provided the towed vehicle(s) has a gross vehicle weight rating (GVWR) of more than 10,000 pounds. Typically, this is the class of CDL you want for operating semi-trucks and tractor-trailers. A Class B CDL allows you to operate a single vehicle with a GVWR of 26,001 pounds or more or a combination vehicle where the towed vehicle has a GVWR of 10,000 pounds or less. This class of CDL is typically for operating large buses and straight trucks, including box trucks and most dump trucks. A Class C CDL allows you to operate other kinds of commercial vehicles that transport hazardous materials or at least 16 occupants (including the driver). This class of CDL is typically for operating small buses (including shuttle buses) or small trucks carrying hazardous materials.
No matter which class of CDL you plan to obtain, you must pass the General Knowledge test on general commercial driving theory and a skills test in a vehicle that’s representative of the class of CDL you’re applying for. But that’s not all. To drive combination vehicles, you must also pass the Combination Vehicles knowledge test on the theory of operating combination vehicles. Both of these knowledge tests are based on the official Iowa National CDL Manual (Iowa CDL Handbook 2026). You should read this study guide a couple of times to learn as much as you can from it. But if you’ve found it tough to learn enough from this handbook to pass the knowledge tests, you probably need some more help.
M.S., Chief Educational Researcher (ACES member)
Last verified for accuracy on
This free Iowa CDL Combination practice test is based on the official CDL manual, just like the official Combination Vehicles knowledge test. It’s up to date as of January, 2026. There are 25 multiple-choice practice questions and answers on such topics as combination braking systems, combination driving techniques, coupling and uncoupling, and pre-trip inspections. Our automated assistant can give you a hint if you get stuck on a question or an explanation of the correct answer if you still miss the question. There’s no time limit; take all the time you need to learn and master the material covered by this practice test.
Be sure to try our other CDL Combination practice tests too.
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Driver handbook • Knowledge‑test/permit overview • Fees & ID requirements • Office/appointment info
We mirror recurring themes (e.g., right‑of‑way traps, sign look‑alikes) and use similar distractors and wording styles.
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