- Updated for March 2025
- Based on 2025 IA commercial driver's license manual
Free IA CDL Double/Triple Trailers Practice Test 2025
Iowa’s agriculture, manufacturing, and logistics sectors depend heavily on trucks for freight transportation. I-35, I-80, and I-380 all support double-trailer trucks. In addition to double-pup trailers (which are allowed nationwide), Iowa also allows Turnpike Double (two full-size trailers) and Rocky Mountain Double (a full-size trailer followed by a pup trailer) truck configurations on designated routes. (Triple trailers are not allowed in Iowa.)
Here are some examples: Cargill, ADM, and CHS Inc. use double grain trailers to move corn and soybeans from farms to processing plants. POET Bioprocessing and Valero Renewables use double tankers for ethanol shipments. John Deere and Vermeer Corporation transport agricultural and construction equipment on double flatbed trailers. Freight companies use Turnpike Doubles and Rocky Mountain Doubles to transport goods between Chicago, Omaha, and Des Moines. UPS and FedEx Ground use double pup trailers for regional package delivery.
If you want to pull doubles or triples, you must obtain a Double/Triple (T) endorsement on your Class A CDL. For this endorsement (assuming you are already qualified to drive combination vehicles), you must pass the official Double/Triple knowledge test (but no additional skills test). This test covers such topics as safe handling, air and electrical lines, coupling and uncoupling, rollovers, and trailer sway.
This knowledge test is based on the official Iowa CDL manual (Iowa CDL Handbook 2025), especially Chapter 7: Doubles and Triples. (You likely studied other parts of this manual to pass your General Knowledge and Combination exams.)
We offer a set of tools to complement the official manual with intensive training. This is the first of our five Iowa Doubles and Triples Endorsement Practice Tests. This practice test is based on the official CDL manual, just like the official Double/Triple knowledge test. It’s up to date as of March, 2025. The 20 multiple-choice practice questions and answers on this practice test address such topics as air lines, converter dollies, coupling, following distance, rearward amplification, and rollovers.
Our AI Assistant can help you answer any practice question. It can give you a hint or an example or answer any of your own questions about driving. If you still miss the question, the AI Assistant will immediately provide you with the correct answer and an explanation. You won’t have to wait till the end of the test to get this information.
This practice test has no time limit; take all the time you need to learn and master the material covered by this practice test. You can retake this practice test as often as you wish until you’ve mastered the material.
- 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)
- When you're pulling more than one trailer, which trailer should be the first one behind the tractor?
- Which of these statements about quick steering movements and doubles/triples is true?
- You are driving a 100-foot double trailer combination at 50 mph. The road is dry and visibility is good. You should keep at least ____ seconds of space ahead of you.
- Before connecting a converter dolly to a second or third trailer, you should check the height of the trailer. The trailer height is right if
- You are driving a 100-foot double trailer combination at 30 mph. The road is dry and visibility is good. You should keep at least ____ seconds of space ahead of you.
- With the hand valve on, you should test the trailer brakes by opening the service line valve at the rear of the rig. When you do this, you should hear
- Empty trucks
- Which of these statements about handling doubles and triples is true?
- Before you can supply air to the air tanks of a second trailer, you need to
- You are driving with double trailers and must use your brakes to avoid a crash. For emergency braking, you should
- How can you be sure that you supplied air to a second trailer?
- What is likely to happen if the pintle hook is unlocked while the dolly is still under the second trailer?
- You want to hook your combination to a second trailer that does not have spring brakes. To do this without wheel chocks, you should
- Which of these statements about managing space to the sides is true?
- The crack-the-whip effect that troubles trucks with trailers is most likely to tip over
- You are visually checking the coupling of a converter dolly to the rear trailer. How much space should there be between the upper and lower fifth wheel?
- You are pulling doubles. A set of trailer wheels goes into a skid. Which of the following is most likely to occur?
- You are doing a walk-around inspection of a double or triple trailer rig. You should be sure that the converter dolly air tank drain valves are ______ and the pintle hook is _______.
- A converter dolly is
- A converter dolly consists of a ______ wheel and ________ axles.
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