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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.
M.S., Chief Educational Researcher (ACES member)
Last verified for accuracy on
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 December, 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.
Driver’s Ed is - nobody wants to set foot inside the DOT. That’s why millions of learners trust us for simple, visual, effective prep.
We are an officially recognized FMCSA Entry-Level Driver Training provider and a proud partner to over 2,500 libraries. We work with safety organizations like GHSA and the National Safety Council to help create safer roads for everyone.
Our trademarked system automatically saves questions you miss, creating personalized tests that target your weak spots until you’ve mastered the material.
Get smarter as you study. Our new AI-powered feedback provides detailed, question-level insights to help you understand the why behind each answer.
Go beyond the boring black-and-white manual. Our interactive handbook lets you read, listen with an MP3 audio version, or even chat with it to find the information you need, faster.
We build our practice questions from the current 2025 IA Driver Handbook and refine them using patterns recent test‑takers report.
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.
We don’t collect or publish actual test items and we’re not affiliated with DOT.
