- Why There's No Official National Pass Rate
- What "Passing" Actually Requires
- Two Knowledge Tests, Two Points of Failure
- Which Domains Cause the Most Trouble
- The TSA Background Check: A Hidden Pass/Fail Gate
- How the ELDT Requirement Changed the Picture
- Building a Preparation Timeline Around the Real Risk Points
- Frequently Asked Questions
- No commercial vendor tracks a national X pass rate because state driver licensing agencies administer both underlying tests.
- A passing score of 80 percent correct is federally mandated on each knowledge test under 49 CFR 383.135.
- X requires passing both the hazmat knowledge test (commonly 30 questions) and the tank vehicle knowledge test (commonly 20 questions).
- First-time H endorsement applicants must also clear a TSA Security Threat Assessment and complete registry-listed ELDT training.
Why There's No Official National Pass Rate
If you've searched for a single published pass rate for the Combination of Tank Vehicle and Hazardous Materials endorsement, you've probably come up empty. That's not an oversight in reporting - it's structural. X is not a standalone certification exam administered by one company that can publish a clean annual statistic. It's a code that appears on a Commercial Driver's License when a driver holds both the Hazardous Materials (H) endorsement and the Tank Vehicle (N) endorsement at the same time. The knowledge tests behind those endorsements are set by the Federal Motor Carrier Safety Administration but actually administered by individual state driver licensing agencies, not a centralized testing vendor.
Because every state runs its own testing infrastructure, question pools, and scheduling systems, there is no single national database tracking how many people attempt the hazmat and tank vehicle knowledge tests together and pass both on the first try. Some states report endorsement-level pass statistics for internal purposes; most don't make combined H+N pass-rate data public. Anyone quoting a specific national pass percentage for X is very likely repeating a number that belongs to an entirely different credential that happens to share the same three-letter shorthand.
What "Passing" Actually Requires
Under 49 CFR 383.135, every CDL knowledge test - including the hazardous materials and tank vehicle tests that combine to form X - requires a score of 80 percent correct to pass. That threshold is not negotiable by state, and it doesn't shift based on test difficulty or question count. On a 30-question hazmat test, 80 percent means missing no more than six questions. On a 20-question tank vehicle test, it means missing no more than four. Those margins are tight enough that guessing your way through unfamiliar material is a poor strategy on either test.
Because the two knowledge tests are graded independently, "passing X" really means clearing two separate 80-percent bars, not averaging your performance across both. A strong tank vehicle score cannot offset a weak hazmat score, and vice versa. If your state licensing agency reports results as pass/fail per endorsement rather than a numeric score, you may not get detailed feedback on which questions you missed - another reason to build a strong knowledge base before you sit for either test rather than treating the first attempt as a diagnostic run.
Two Knowledge Tests, Two Points of Failure
Most candidates think of X as one credential, but from a preparation standpoint it behaves like two exams stacked on top of each other. The required knowledge areas are defined separately in federal regulation: 49 CFR 383.121 governs hazardous materials content, and 49 CFR 383.119 governs tank vehicle content. Each test draws from its own regulatory source, uses its own question style, and tests a different mental model of the job.
- Hazardous materials knowledge test: commonly 30 questions, drawn from regulatory and procedural material - shipping papers, placarding rules, packaging requirements, and communication of hazards.
- Tank vehicle knowledge test: commonly 20 questions, drawn from vehicle-handling physics and mechanical concepts - surge, baffling, braking dynamics, and tank construction differences.
Because these are conceptually different bodies of knowledge, candidates who cram only one side often discover the gap on test day. A driver who has spent years hauling dry freight may know placarding rules cold but have never thought about how an unbaffled tank behaves on a curve. A driver who has hauled liquid bulk for years may intuitively understand cargo surge but be shaky on the Hazardous Materials Table. Treat X prep as two study tracks that happen to lead to one endorsement code, and use a resource that separates them clearly, like the X Exam Domains 2026: Complete Guide to All 10 Content Areas, so you know exactly which track a given topic belongs to.
Which Domains Cause the Most Trouble
Across the ten content domains that make up X preparation, the material isn't distributed evenly. The heaviest content block by far is hazardous materials regulations - it covers the Hazardous Materials Table, shipping papers, marking, labeling, placarding, packaging, ORM-D material, hazmat accident reporting, and rules for tunnels and railroad crossings. That density is exactly why Domain 1 tends to be where candidates lose the most points.
Domain 1: Hazardous Materials Regulations
This domain carries the largest volume of memorization-heavy detail on the entire exam. Candidates need to be fluent in reading the Hazardous Materials Table, matching placards to hazard classes, and knowing documentation sequence on shipping papers.
- Correctly identifying proper shipping name, hazard class, and packing group from the table
- Placarding thresholds and when a placard is required versus optional
- Reporting obligations after a hazmat incident
Domain 5 & 7: Cargo Surge and Baffling Effects
On the tank vehicle side, the two concepts that trip up otherwise well-prepared candidates are cargo surge dynamics and the difference between baffled, compartmented, and non-baffled tanks. These are physical, scenario-based questions rather than pure recall.
- How liquid movement inside a partially full tank affects steering and braking
- Why non-baffled tanks (common in liquid fuel hauling) demand different driving techniques than baffled tanks
Because Domain 1 is disproportionately large and Domains 5 through 9 require applied reasoning rather than memorization, a study plan that treats every domain as equal in weight is a mistake. If you haven't already mapped out how the ten domains relate to the two underlying tests, the X Exam Domains 2026: Complete Guide to All 10 Content Areas breaks down exactly which domains feed the hazmat test and which feed the tank vehicle test.
Key Takeaway
Allocate more study time to Domain 1 (Hazardous Materials Regulations) than to any single tank vehicle domain - it's the largest content block and the one most likely to determine whether you clear the 80 percent threshold on the hazmat test.
The TSA Background Check: A Hidden Pass/Fail Gate
Passing the written hazmat knowledge test isn't the only barrier standing between a driver and the H endorsement half of X. Every applicant must also clear a TSA Security Threat Assessment, which includes fingerprinting. As of January 1, 2025, the fee is $85.25 for both new and renewing applicants, with a reduced rate of $41.00 available to applicants who already hold a valid TWIC card in a state that accepts TWIC comparability.
This background check functions as a second, non-academic pass/fail gate. A candidate can score well above 80 percent on both knowledge tests and still be unable to receive the H endorsement - and therefore the combined X code - if the threat assessment flags a disqualifying issue. Anyone budgeting time and money for this credential should treat the TSA process as a parallel track that needs to start early, not an afterthought handled after the knowledge tests are passed. For a full breakdown of every fee involved, see X Certification Cost 2026: Complete Pricing Breakdown.
How the ELDT Requirement Changed the Picture
Since February 7, 2022, first-time applicants for the H endorsement must complete hazardous materials entry-level driver training from a provider listed on the FMCSA Training Provider Registry before they can even sit for the hazmat knowledge test. This training requirement applies specifically to the hazmat side of X; the tank vehicle endorsement has no equivalent ELDT mandate.
This asymmetry matters for anyone estimating how long the whole process will take. A driver pursuing the tank vehicle endorsement alone can often move from decision to testing fairly quickly, limited mainly by scheduling at their state licensing agency. A driver pursuing the H endorsement - a mandatory piece of X - has an additional training step built into the front of the process, on top of the TSA background check. If you're mapping out a realistic timeline toward earning X, the training requirement and the background check both need to be sequenced before you assume you can walk in and test. Details on how these pieces fit together are covered in X Requirements 2026: Eligibility, Prerequisites & How to Qualify.
| Requirement | Hazmat (H) Side | Tank Vehicle (N) Side |
|---|---|---|
| Governing regulation | 49 CFR 383.121 | 49 CFR 383.119 |
| Typical question count | 30 questions | 20 questions |
| Passing score | 80% (49 CFR 383.135) | 80% (49 CFR 383.135) |
| ELDT required? | Yes, since Feb. 7, 2022 | No |
| TSA background check | Required ($85.25 new/renewing, $41.00 with comparable TWIC) | Not required |
| Renewal cycle | Every 5 years, new threat assessment | Follows state CDL renewal cycle |
Building a Preparation Timeline Around the Real Risk Points
Generic study advice tends to assume one exam with one syllabus. X doesn't work that way - you're preparing for two distinct knowledge tests with different formats, plus a non-academic background check running in parallel. A workable timeline treats those as separate tracks that converge at the state testing window.
Hazmat regulations foundation
- Start the ELDT training requirement if pursuing the H endorsement for the first time
- Begin working through the Hazardous Materials Table and shipping paper rules - Domain 1
Marking, labeling, and placarding
- Drill placard thresholds and hazard class identification
- Cover Domains 2 through 4: hazmat handling, emergency equipment, and response procedures
Tank vehicle physics
- Shift focus to cargo surge (Domain 5) and braking behavior on empty, full, and partially full tanks (Domain 6)
- Compare baffled versus non-baffled tank handling (Domain 7)
Vehicle construction and road conditions
- Review tank vehicle type and construction differences (Domain 8) and grade/curvature effects (Domain 9)
- Take full-length practice tests for both the hazmat and tank vehicle formats
Notice this timeline never mixes hazmat and tank vehicle content in the same week for the first two weeks - that separation matters because the two tests use different reasoning styles, and switching between memorization-heavy regulatory content and applied vehicle-dynamics content too quickly tends to blur both. If you want a structured week-by-week plan with more detail, our X Study Guide 2026: How to Pass on Your First Attempt expands on this approach, and you can benchmark your readiness against realistic questions using the practice tests on the main site.
Who Actually Needs to Clear Both Tests
Understanding who pursues X helps explain why the combined endorsement exists at all. Carriers that move liquid or gaseous hazardous materials in bulk - a tank vehicle is defined as one carrying liquid or gaseous material in a tank with an individual rated capacity over 119 gallons and an aggregate capacity of 1,000 gallons or more - need drivers who can legally haul both the hazardous cargo and operate the tank equipment itself. That's precisely the gap X closes: a driver with only the H endorsement can haul hazmat in a dry van but not a tanker; a driver with only the N endorsement can haul non-hazardous liquids but not, say, flammable fuel. Fleets running fuel delivery, chemical transport, or bulk liquid hazmat routes typically require the combined credential as a condition of hire. If you're evaluating whether this career path fits your goals, X Jobs and Is the X Certification Worth It? Complete ROI Analysis 2026 go deeper into the hiring landscape and compensation considerations.
Frequently Asked Questions
No. Because state driver licensing agencies, not a centralized testing vendor, administer the underlying hazmat and tank vehicle knowledge tests, there is no single national pass-rate figure published for the combined X endorsement.
Federal regulation 49 CFR 383.135 requires 80 percent correct on each knowledge test. That applies separately to the hazmat test and the tank vehicle test - you must clear both.
Yes. The TSA Security Threat Assessment is a separate requirement from the written tests. A driver can score above 80 percent on both exams and still be denied the H endorsement if the background check identifies a disqualifying issue.
No. Since February 7, 2022, first-time H endorsement applicants must complete entry-level driver training from an FMCSA registry provider. The tank vehicle (N) endorsement carries no equivalent training requirement.
Every five years, and renewal requires completing a new TSA Security Threat Assessment, not just retesting on knowledge content.
Because so much of X's difficulty comes from regulatory density and mechanical dynamics rather than trick questions, the most reliable path forward is disciplined coverage of both the domain structure and the fee and eligibility mechanics outlined here. For a deeper look at how challenging candidates generally find the combined endorsement, see How Hard Is the X Exam? Complete Difficulty Guide 2026, and when you're ready to test your knowledge under realistic conditions, the question banks on our practice test platform mirror the domain breakdown covered above.