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- Updated for January 2025
- Based on 2025 IA commercial driver's license manual
Free Iowa CDL Combination Practice Test 2025
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 2025). 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.
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, 2025. 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.
- Perfect for first-time and renewal CDL/CLP applicants, and those adding endorsements
- Triple-checked for accuracy
What you need to know
What to expect on the actual IA DOT exam
questions
correct answers to pass
passing score
List of questions (classic view)
- After you lock the kingpin into the fifth wheel, you should check the connection by pulling
- After connecting the air lines but before backing under the trailer, you should
- Which statement best illustrates the "crack-the-whip" effect?
- Where should the tractor be when you inspect the landing gear after uncoupling the trailer?
- What is the safest way for you to make a turn without entering another traffic lane?
- To drive a triple combination vehicle, you must have
- To prevent rollover, cargo should be
- Combination vehicles take longer to stop when they are empty than when they are fully loaded, because
- If your vehicle gets stuck on a railroad track, you should
- Low-slung vehicles can be risky at railroad crossings because
- On a double or triple vehicle, which wheels offtrack the most?
- When you're pulling doubles or triples, the shut-off valves should always be
- On a trailer, where is the yellow antilock brake (ABS) malfunction lamp located?
- Even before antilock braking systems (ABS) were required, some vehicles already had them. How can you check if your vehicle has ABS?
- An antilock braking system (ABS) is useful
- After coupling, make sure that the air lines are not crossed. How should you do this?
- During uncoupling, you should disconnect the electrical cable and
- Before you start to uncouple, you must
- You can confirm that air is going to all brakes in your trailers by
- To uncouple a loaded trailer, after the landing gear has made firm contact with the ground, you should
- If the trailer has antilock brakes (ABS) but the tractor doesn't,
- To test the tractor protection valve, charge the trailer air brake system, turn off the engine, and
- If your test of the tractor protection valve is successful,
- The tractor protection valve is designed to close automatically when the air pressure falls into the pressure range specified by the manufacturer, typically
- As part of your vehicle inspection test, if your vehicle is equipped with air brakes and has a trailer, you will inspect the air connections between the truck or tractor and the trailer. Make sure that the ________ are locked in place and free of damage or air leaks.
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