- The Real Passing Score for X
- Two Tests, One Code: Why X Isn't a Single Exam
- What's Actually Tested: Domain-by-Domain Breakdown
- Question Format and What "80 Percent" Really Means
- Fees, TSA Screening, and Eligibility Mechanics
- A Domain-Focused Study Schedule
- Who Actually Needs the X Endorsement
- Frequently Asked Questions
- Both the hazmat and tank vehicle knowledge tests require 80 percent correct under 49 CFR 383.135.
- X is a CDL code, not a standalone exam - it appears once you hold both the H and N endorsements.
- The hazmat test commonly runs 30 questions; the tank vehicle test commonly runs 20 questions.
- First-time H applicants must complete FMCSA-registered entry-level driver training before testing.
The Real Passing Score for X
If you searched for the X passing score, the honest answer is a federal number, not a marketing number: 80 percent correct on each knowledge test, as mandated by 49 CFR 383.135. There is no separate "X exam" with its own scoring curve. This is the same passing threshold applied nationwide to every knowledge test that state driver licensing agencies administer for CDL endorsements.
Because X requires two endorsements - Hazardous Materials (H) and Tank Vehicle (N) - you actually need to clear 80 percent twice: once on the hazmat knowledge test and once on the tank vehicle knowledge test. Missing the mark on either one means you don't get the combined code, even if your other score was strong.
Two Tests, One Code: Why X Isn't a Single Exam
A lot of confusion around this credential starts with the letter itself. X is the code that appears on a Commercial Driver's License when a driver holds both the H and N endorsements simultaneously. There is no unified "X test booklet" you sit down and take in one sitting. Instead, you pass the hazardous materials knowledge test governed by 49 CFR 383.121, and you pass the tank vehicle knowledge test governed by 49 CFR 383.119. Once both are on your record, your state prints the combined X designation.
This distinction matters for how you prepare. If you're researching study strategy, our X Study Guide 2026: How to Pass on Your First Attempt walks through building a prep plan that treats these as two related but distinct knowledge tests rather than one monolithic exam.
Key Takeaway
Budget separate study time for hazmat regulations and for tank vehicle handling - they draw from different regulatory sections and different skill sets.
What's Actually Tested: Domain-by-Domain Breakdown
The combined X credential draws from ten content areas that span both underlying tests. Understanding which domain belongs to which test - and how heavily it's weighted - is the single biggest lever you have for efficient study. For a deeper walkthrough of each area, see our X Exam Domains 2026: Complete Guide to All 10 Content Areas.
Domain 1: Hazardous Materials Regulations
This is the heaviest content block on the hazmat side. Expect questions on the Hazardous Materials Table, shipping papers, marking, labeling, placarding, packaging, ORM-D classifications, hazmat accident reporting, and rules for tunnels and railroad crossings.
- Know how to read and cross-reference the Hazardous Materials Table
- Understand placarding thresholds and label placement rules
Domain 2: Hazardous Materials Handling
Covers safe loading, unloading, segregation of incompatible materials, and proper container handling procedures required under the hazmat knowledge test standards.
- Segregation tables and incompatible material pairings
- Loading and securement of hazardous packages
Domain 3: Operation of Emergency Equipment
Tests your familiarity with fire extinguishers, spill kits, and emergency shutoffs specific to hazmat transport.
Domain 4: Emergency Response Procedures
Covers what a driver must do immediately following a spill, leak, or accident involving hazardous cargo, including reporting obligations.
Domain 5: Causes, Prevention, and Effects of Cargo Surge on Vehicle Handling
This is a tank vehicle-specific concept. Liquid surge inside a partially full tank shifts vehicle weight during braking and turning, and candidates must understand how to anticipate and counteract it.
Domain 6: Braking Procedures for Empty, Full, and Partially Full Tanks
Tank vehicles behave differently depending on fill level. Expect scenario questions comparing stopping distance and control at each fill state.
Domain 7: Baffled and Compartmented Versus Non-Baffled Tank Handling
Baffles reduce surge; non-baffled tanks (common with liquid food-grade or certain chemical loads) require more conservative driving techniques. Know the practical driving differences between the two designs.
Domain 8: Tank Vehicle Type and Construction Differences
Covers how a tank vehicle is legally defined - a tank with individual rated capacity over 119 gallons and an aggregate capacity of 1,000 gallons or more - plus construction variations across tank types.
Domain 9: Effects of Road Grade and Curvature on Tank Vehicle Handling
Tests understanding of how elevation changes and curves interact with a high center of gravity and shifting liquid loads.
Domain 10: Proper Use of Emergency Systems
Focuses on tank-specific emergency shutoff valves, venting systems, and rollover protection features.
Notice the pattern: Domains 1 through 4 map to the hazmat knowledge test, while Domains 5 through 10 map to the tank vehicle knowledge test. If a topic feels unusually difficult to pin down, our How Hard Is the X Exam? Complete Difficulty Guide 2026 breaks down which domains tend to trip up candidates and why.
Question Format and What "80 Percent" Really Means
The hazmat knowledge test is commonly structured around 30 questions, while the tank vehicle knowledge test is commonly structured around 20 questions. Because the passing threshold is a percentage rather than a fixed question count, the practical math looks different for each test:
| Knowledge Test | Typical Question Count | Passing Requirement | Governing Regulation |
|---|---|---|---|
| Hazardous Materials (H) | 30 questions | 80% correct | 49 CFR 383.121 / 383.135 |
| Tank Vehicle (N) | 20 questions | 80% correct | 49 CFR 383.119 / 383.135 |
Because state agencies administer the actual tests, exact question pools, wording, and scheduling procedures can vary slightly by state. What doesn't vary is the federal 80 percent floor. For a sense of how candidates perform against that floor in aggregate, review our X Pass Rate 2026: What the Data Shows article.
Fees, TSA Screening, and Eligibility Mechanics
Passing the knowledge tests is only part of earning X. The hazmat side carries extra federal security requirements that the tank vehicle side does not.
- TSA Security Threat Assessment: Required for the H endorsement, involving fingerprinting. As of January 1, 2025, the fee is $85.25 for new and renewing applicants, or $41.00 if you already hold a valid TWIC in a state that accepts comparability.
- Entry-Level Driver Training (ELDT): Since February 7, 2022, first-time H endorsement applicants must complete hazmat-specific training through a provider listed on the FMCSA Training Provider Registry before testing. The tank vehicle (N) endorsement has no ELDT requirement.
- Renewal cycle: The endorsement is renewed every five years, and each renewal requires a fresh threat assessment.
For a full cost picture including state fees that vary by jurisdiction, see X Certification Cost 2026: Complete Pricing Breakdown. If you're still confirming whether you qualify to apply at all, our X Requirements 2026: Eligibility, Prerequisites & How to Qualify guide covers prerequisite driving privileges and documentation.
Key Takeaway
Schedule your TSA fingerprinting appointment early - the background check timeline can be the longest step in the entire process, longer than studying for either knowledge test.
A Domain-Focused Study Schedule
Generic study techniques only help if they're mapped onto the actual content split between the two tests. Here's a four-week structure built around the ten domains rather than around study theory for its own sake.
Hazmat Regulations Foundation (Domains 1-2)
- Work through the Hazardous Materials Table until you can locate entries quickly
- Drill shipping papers, marking, labeling, and placarding rules
- Review ORM-D handling and segregation requirements
Hazmat Emergency Content (Domains 3-4)
- Memorize accident and spill reporting thresholds
- Practice scenario questions on emergency equipment operation
- Take a full practice run of the 30-question format
Tank Vehicle Dynamics (Domains 5-8)
- Study cargo surge causes and how baffled vs. non-baffled tanks respond
- Compare braking behavior across empty, full, and partial fill states
- Review the legal definition of a tank vehicle and construction types
Road Conditions and Systems, Then Full Review (Domains 9-10)
- Study grade and curvature effects on high-center-of-gravity vehicles
- Review emergency shutoff and venting system procedures
- Run a full 20-question practice test and revisit weak domains
Practicing under realistic question conditions before test day matters more than re-reading regulations passively. You can run through timed scenarios on our practice test platform to get a feel for how these questions are actually phrased.
Who Actually Needs the X Endorsement
The combined X code shows up on the CDLs of drivers who regularly haul liquid or gaseous hazardous materials in bulk tanks - think fuel haulers, chemical transport drivers, and certain agricultural or industrial liquid carriers. A tank vehicle, by definition, carries material in a tank with individual rated capacity over 119 gallons and an aggregate capacity of 1,000 gallons or more, so smaller container hazmat loads that don't meet that threshold wouldn't require the N portion, only the H.
Carriers hiring for these positions typically need documented proof of both endorsements before dispatching a driver on tank routes carrying regulated hazardous materials. If you're evaluating whether pursuing this path fits your career goals, our X Salary Guide 2026: Complete Earnings Analysis and Is the X Certification Worth It? Complete ROI Analysis 2026 articles look at the practical trade-offs. For a broader look at open positions, check X Jobs.
Once you're confident in the fee structure and domain content, a condensed one-page reference can help during final review. Our X Cheat Sheet 2026: One-Page Review of Must-Know Facts consolidates the regulatory citations and thresholds covered here into a quick-scan format. You'll also want to confirm your state's specific scheduling process - see X Exam Dates 2026: Testing Windows, Deadlines & Scheduling for how to book your knowledge test appointments. Running a few timed sessions on our practice tests before your actual appointment is one of the most reliable ways to confirm you're consistently clearing the 80 percent line on both tests.
Frequently Asked Questions
No. Both knowledge tests require 80 percent correct, per the federal standard in 49 CFR 383.135. The tests differ in content and typical question count, not in the score you need to pass.
Two separate knowledge tests. X is the CDL code that appears once you've passed both the hazardous materials knowledge test and the tank vehicle knowledge test and hold both endorsements.
The hazmat knowledge test commonly has 30 questions, and the tank vehicle knowledge test commonly has 20 questions. You need 80 percent correct on each.
No. First-time H endorsement applicants must complete entry-level driver training from an FMCSA Training Provider Registry provider, a requirement in place since February 7, 2022. The tank vehicle (N) endorsement has no ELDT requirement.
The endorsement is renewed every five years, and each renewal requires a new TSA Security Threat Assessment, currently $85.25 for new and renewing applicants or $41.00 with an accepted TWIC.