Last updated: March 14, 2026 · By Free CDL Quiz Editorial Team
Preparing for your Iowa CDL exam? This guide covers all 8 CDL test categories you may encounter at the Iowa DOT: General Knowledge, Air Brakes, Combination Vehicles, HazMat, Tanker, Doubles/Triples, Passenger, and School Bus. Each section explains what the test covers, how many questions to expect, and links to a free IA practice test for that category.
The General Knowledge test is required for all CDL applicants regardless of vehicle class. It covers safe driving practices, vehicle inspection, cargo handling, transporting passengers, air brakes basics, and federal regulations. This is the foundation of every CDL — you cannot get your Commercial Learner's Permit without passing it.
The Air Brakes test is required if you plan to drive any commercial vehicle equipped with air brakes — which includes most trucks and buses. If you do not pass this test, your CDL will carry an air brake restriction that limits the types of vehicles you can drive.
The Combination Vehicles test is required for Class A CDL applicants who plan to drive a tractor-trailer or other combination vehicle. It covers coupling and uncoupling procedures, safe driving techniques specific to articulated vehicles, and rollover prevention.
The HazMat endorsement (H) is required to transport hazardous materials in quantities that require placarding. This endorsement requires both a written test and a TSA background check. HazMat-endorsed drivers are among the highest-paid in the industry.
The Tanker endorsement (N) is required to haul liquid cargo in bulk. Tanker vehicles have a high center of gravity and are prone to rollovers, making specialized knowledge essential for safe operation. Drivers with Tanker and HazMat endorsements (X endorsement) are in high demand.
The Doubles/Triples endorsement (T) allows you to pull double or triple trailers. These longer combination vehicles require specialized knowledge about coupling, turning, and managing trailer sway. Not all states allow triple trailers on their roads.
The Passenger endorsement (P) is required to drive vehicles designed to transport 16 or more passengers (including the driver). This includes transit buses, charter buses, and intercity buses. A road skills test in a passenger vehicle is also required.
The School Bus endorsement (S) is required to drive a school bus. Because you are transporting children, this endorsement has the strictest requirements. A road skills test in a school bus is also required, and most states require additional background checks.
The CDL tests you need in Iowa depend on your vehicle class and what you plan to haul. Here is a quick breakdown:
| CDL Class / Goal | Required Tests |
|---|---|
| Class A (tractor-trailer) | General Knowledge + Combination Vehicles + Air Brakes |
| Class B (straight truck, bus) | General Knowledge + Air Brakes (if applicable) |
| Hauling hazardous materials | + HazMat endorsement test + TSA background check |
| Hauling liquid tankers | + Tanker endorsement test |
| Pulling doubles/triples | + Doubles/Triples endorsement test |
| Driving a bus (16+ passengers) | + Passenger endorsement test + skills test |
| Driving a school bus | + School Bus endorsement test + skills test + background check |
To prepare for your IA CDL exam, we recommend combining practice tests with the official Iowa CDL handbook and our comprehensive study guide.
Practice all 8 CDL test categories for Iowa right now — free, no signup required.
Start Practicing for FreeThere are 8 CDL written test categories in Iowa: General Knowledge (required for all), Air Brakes, Combination Vehicles, HazMat, Tanker, Doubles/Triples, Passenger, and School Bus. The tests you need depend on your vehicle class and the endorsements you want. All tests are administered by the Iowa DOT.
The passing score for all CDL written tests in Iowa is 80%. For the General Knowledge test, that means answering at least 40 out of 50 questions correctly. Endorsement tests typically have 20-30 questions. You can retake a failed test after a short waiting period at the Iowa DOT.
Yes, most Iowa DOT locations allow you to take multiple CDL endorsement tests on the same day. You must pass each test separately. Prepare for all categories using FreeCDLQuiz.com before your appointment to maximize your chances of passing everything in one visit.
In Iowa, the HazMat (H) and Tanker (N) endorsements — or the combined HazMat-Tanker (X) endorsement — typically command the highest pay premiums. Drivers with HazMat endorsements earn an average of $5,000-$10,000 more per year. Doubles/Triples (T) is also in demand in Iowa due to freight and distribution activity.
FreeCDLQuiz.com offers free practice tests for every CDL category in Iowa — General Knowledge, Air Brakes, Combination Vehicles, HazMat, Tanker, Doubles/Triples, Passenger, and School Bus. No login required, with 500+ questions and detailed explanations aligned with the IA CDL handbook.