- Overview: The Eight Content Areas of the KY-CDL Permit Test
- Domain 1: General Knowledge Test
- Domain 2: Combination Vehicles Test
- Domain 3: Air Brakes Test
- Domain 4: Doubles/Triples Trailers Test
- Domain 5: Tankers Test
- Domain 6: Passenger Transport Test
- Domain 7: Hazardous Materials Test
- Domain 8: School Bus Test
- Fees and Retest Costs by Domain
- Scheduling Domains Around a Study Plan
- Frequently Asked Questions
- The KY-CDL Permit Test has 8 content areas, each tied to a specific endorsement or vehicle class.
- General Knowledge has 50 questions; most endorsement tests have 20-30 questions, all requiring 80% to pass.
- Every domain except Hazardous Materials can be taken as a written or oral test.
- Failed knowledge tests require a 24-hour wait, and retests after Combination Vehicles, Air Brakes, or endorsement failures cost $5.
Overview: The Eight Content Areas of the KY-CDL Permit Test
If you're preparing for a commercial driver license in Kentucky, the first thing to understand is that "the exam" isn't one test - it's up to eight separate knowledge tests, each covering a distinct content area. Which ones you need depends on the vehicle class you'll drive and the endorsements your job requires. This guide breaks down all eight domains in the order most candidates encounter them, with the exact question counts and pass thresholds from the current Kentucky CDL manual (Version March 2025).
Kentucky State Police administers the knowledge, vision, and skills testing, while the Kentucky Transportation Cabinet issues the actual credential once you've cleared every required step. Every applicant starts with General Knowledge, then adds whichever combination of the remaining seven domains matches their intended driving job. For a broader look at eligibility before you even sit for a test, see our KY-CDL Requirements guide.
Domain 1: General Knowledge Test
General Knowledge Test - 50 Questions
This is the foundational test every CDL applicant must pass, regardless of vehicle class. It covers the core rules and safe-driving practices that apply across all commercial vehicles.
- Basic vehicle inspection and pre-trip procedures
- Safe driving techniques, following distance, and speed management
- Vehicle control systems and warning devices
- Rules around hours of service, driver fitness, and documentation basics
Because General Knowledge has the largest question count of all eight domains, it's usually the section candidates spend the most preparation time on. It can be taken as a written or oral test. For a deeper walkthrough of exactly how many correct answers you need and how scoring works across every domain, check the KY-CDL Passing Score breakdown.
Domain 2: Combination Vehicles Test
Combination Vehicles Test - 20 Questions
Required for anyone operating a tractor-trailer or other combination unit, this domain focuses on the added complexity of coupling multiple vehicle sections together.
- Coupling and uncoupling procedures
- Combination vehicle inspection points
- Handling characteristics unique to articulated units, including off-tracking and stability
- Emergency procedures specific to combination rigs
If you fail this test after your initial attempt, a $5 retest fee applies, and you must wait 24 hours before retaking it. Candidates aiming for over-the-road freight jobs almost always need this domain alongside General Knowledge.
Domain 3: Air Brakes Test
Air Brakes Test - 25 Questions
Nearly every commercial truck and bus in Kentucky uses air brake systems, which makes this one of the most consequential domains on the exam. Skipping it restricts you to air-brake-free vehicles only - a serious limitation for most driving jobs.
- Air brake system components and how they interact
- Dual air brake systems and low-pressure warning devices
- Air brake inspection procedures during pre-trip checks
- Stopping distance and brake fade concepts
Like Combination Vehicles, a failed Air Brakes test carries a $5 retest fee after the first attempt. Many candidates underestimate this domain because it feels technical, but it's a common area where preparation pays off directly. Our difficulty guide covers where Air Brakes ranks among the toughest sections for first-time test takers.
Domain 4: Doubles/Triples Trailers Test
Doubles/Triples Trailers Test - 20 Questions
This endorsement test is required for anyone pulling more than one trailer at a time. It builds directly on Combination Vehicles knowledge but adds the specific hazards of multi-trailer operation.
- Coupling and inspection sequences for multiple trailers
- Handling risks like rearward amplification and crack-the-whip effect
- Proper trailer order and load distribution
- Emergency maneuvers unique to doubles and triples combinations
This test can be taken written or oral. It's a smaller domain by question count, but the concepts are unforgiving - misjudging multi-trailer dynamics is one of the more serious real-world risks this test is designed to screen for.
Domain 5: Tankers Test
Tankers Test - 20 Questions
Required for hauling liquids or gases in bulk tanks, this domain addresses the unique stability and control issues that come with a shifting, partially filled load.
- Surge effects from liquid movement inside partially filled tanks
- Baffled versus unbaffled tank differences
- Tank vehicle inspection requirements
- Turning, braking, and curve-handling adjustments for high centers of gravity
Drivers who plan to work in fuel delivery, food-grade liquid transport, or similar roles will need this endorsement in addition to General Knowledge and often Combination Vehicles or Air Brakes.
Domain 6: Passenger Transport Test
Passenger Transport Test - 20 Questions
This domain applies to anyone driving vehicles designed to carry passengers, such as buses or vans configured for passenger service.
- Passenger loading and unloading procedures
- Emergency exit and evacuation protocols
- Vehicle inspection points specific to passenger-carrying vehicles
- Rules for standing passengers, aisles, and prohibited items
Passenger Transport can be taken written or oral. Candidates pursuing transit, charter, or shuttle driving roles typically pair this endorsement with General Knowledge and, depending on the vehicle, Air Brakes.
Domain 7: Hazardous Materials Test
Hazardous Materials Test - 30 Questions
This is the largest endorsement test outside of General Knowledge, and it's the one domain that cannot be taken orally - it must be completed in written form. The added length and lack of an oral option reflect the regulatory weight of transporting hazardous cargo.
- Hazard classes and placarding requirements
- Shipping paper documentation rules
- Loading, segregation, and containment requirements
- Emergency response and incident reporting basics
Because this domain carries federal security-related implications, many candidates find it requires more dedicated study time relative to its question count than other endorsements. If you're deciding whether the extra effort is worth it for your career goals, our ROI analysis weighs endorsement value against the time investment.
Key Takeaway
Hazardous Materials is the only domain with no oral testing option - plan to study written terminology and placarding rules thoroughly rather than relying on verbal test-taking strategies.
Domain 8: School Bus Test
School Bus Test - 20 Questions
This domain is required specifically for driving school buses and layers additional student-safety procedures on top of the Passenger Transport content.
- Student loading and unloading safety zones
- Railroad crossing procedures specific to school buses
- Emergency evacuation drills for student passengers
- Daily inspection requirements unique to school bus operation
School Bus can be taken written or oral, and it's almost always combined with Passenger Transport since the two domains overlap heavily in real-world application. Districts and bus contractors hiring for these routes typically require both endorsements before a candidate is cleared to drive.
Fees and Retest Costs by Domain
Every domain shares the same 80% passing threshold, but the costs around testing and retesting are worth understanding before you schedule anything. The standard one-year commercial permit costs $11 ($14 if you want a REAL ID-compliant version), plus a $3 NCIC fee. Once you've passed the relevant knowledge tests and held your permit for the required period, an original CDL add-on ranges from $18.75 to $50 depending on credential type and how much time remains before renewal.
| Domain | Question Count | Oral Option |
|---|---|---|
| General Knowledge | 50 | Yes |
| Combination Vehicles | 20 | Yes |
| Air Brakes | 25 | Yes |
| Doubles/Triples Trailers | 20 | Yes |
| Tankers | 20 | Yes |
| Passenger Transport | 20 | Yes |
| Hazardous Materials | 30 | No |
| School Bus | 20 | Yes |
If you fail any knowledge test, you must wait 24 hours before retesting. Combination Vehicles, Air Brakes, and endorsement retests each cost $5 after the initial failed attempt. For a complete line-item breakdown of every fee involved from permit to full CDL issuance, see our KY-CDL Certification Cost guide.
Scheduling Domains Around a Study Plan
Not every candidate needs all eight domains - most need General Knowledge plus two or three others based on the job they're targeting. Once you know your required domains, sequencing your study time matters more than cramming everything at once.
General Knowledge Foundations
- Work through all core rules and inspection procedures - this is your largest domain at 50 questions
- Take practice questions daily to build baseline familiarity with test format
Vehicle-Specific Domains
- Study Combination Vehicles and Air Brakes together since they overlap in inspection concepts
- Focus extra time on Air Brakes given its technical depth
Endorsement Domains
- Add Tankers, Doubles/Triples, Passenger Transport, or School Bus depending on your target job
- Review Hazardous Materials separately since it has no oral testing option and the most questions after General Knowledge
Full Review and Scheduling
- Take full-length practice runs for each required domain
- Schedule your actual test dates and confirm CLP timing ahead of skills testing
This kind of structured pacing - breaking a large content set into weekly domain blocks - is one of the most effective ways to avoid last-minute overload. For a more detailed first-attempt strategy across all domains, read the KY-CDL Study Guide. And if you want to know how testing windows and scheduling deadlines actually work in practice, our Exam Dates guide covers that in full.
Once you're comfortable with the material, running through timed questions on our KY-CDL practice test platform is the most direct way to see which domains still need work before test day.
Who Actually Needs Which Domains
Understanding the eight domains only matters if you connect them to real hiring needs. Freight and trucking employers generally require General Knowledge, Combination Vehicles, and Air Brakes at minimum. Tanker and hazmat carriers add those two respective endorsements on top. Transit authorities and school districts require Passenger Transport, with School Bus added for student transportation roles specifically. If you're still exploring whether this career path fits your goals, our KY-CDL Jobs overview and Salary Guide break down how endorsement combinations align with different driving roles.
For readers who landed here still sorting out terminology, it's worth clarifying that this guide covers the Kentucky CDL Permit Test exclusively - see our companion pieces on What Is KY-CDL? and KY-CDL Meaning if you need that foundational context before diving into domain-level prep. You can also explore the full practice test suite to try sample questions from each domain before committing to a study schedule.
Frequently Asked Questions
No. General Knowledge is required for every applicant, but the other seven domains are only required based on the vehicle class and endorsements your driving job needs.
Yes, for seven of the eight domains. Hazardous Materials is the exception - it must be completed as a written test only.
You must wait 24 hours before retesting. Combination Vehicles, Air Brakes, and endorsement retests carry a $5 fee after the first failed attempt.
Yes, every domain - from General Knowledge's 50 questions to the 20-question endorsement tests - requires an 80% score to pass.
You can take the knowledge tests as soon as you're eligible, but you must hold your CLP for 14 days before you're allowed to schedule skills testing.