- X is the combined H + N code on a CDL, requiring passes on two separate knowledge tests.
- Both the hazmat and tank vehicle knowledge tests require 80 percent correct under 49 CFR 383.135.
- Hazmat tests run about 30 questions; tank vehicle tests run about 20 questions.
- New/renewing TSA threat assessment fees are $85.25, or $41.00 with a comparable valid TWIC.
What This Cheat Sheet Covers
This is a compressed, one-page-style reference for the Combination of Tank Vehicle and Hazardous Materials endorsement - the code that appears on a CDL when a driver holds both the Hazardous Materials (H) and Tank Vehicle (N) endorsements together. It is not a separate exam administered by a private testing company; the standards come from the Federal Motor Carrier Safety Administration under 49 CFR Part 383, and the actual knowledge tests are given by state driver licensing agencies. If you want the long-form version of everything summarized here, pair this page with the full X Study Guide 2026: How to Pass on Your First Attempt and the X Exam Domains 2026: Complete Guide to All 10 Content Areas for deeper domain breakdowns.
Use this page the night before your test, during a lunch-break review, or as your final pass through both knowledge areas. Every fact below is drawn directly from federal regulation and endorsement structure - nothing generic.
The Core Numbers You Must Memorize
These are the numbers examiners assume you already know cold. Do not walk into either knowledge test without them memorized.
| Item | Detail |
|---|---|
| Passing score (each test) | 80 percent correct, per 49 CFR 383.135 |
| Hazmat knowledge test length | Commonly 30 questions |
| Tank vehicle knowledge test length | Commonly 20 questions |
| Governing regulation, hazmat | 49 CFR 383.121 |
| Governing regulation, tank vehicle | 49 CFR 383.119 |
| Tank vehicle definition | Tank(s) with individual rated capacity over 119 gallons and aggregate capacity of 1,000+ gallons |
| TSA threat assessment fee (new/renewing) | $85.25, effective January 1, 2025 |
| TSA threat assessment fee (valid comparable TWIC) | $41.00 |
| Endorsement renewal cycle | Every 5 years, with a new threat assessment |
| Hazmat entry-level driver training | Required since February 7, 2022, for first-time H applicants; not required for N |
For a full cost breakdown that goes beyond this table, see X Certification Cost 2026: Complete Pricing Breakdown, and for the exact scoring mechanics behind the 80 percent threshold, check X Passing Score 2026: Exactly What You Need to Pass.
Key Takeaway
Because X requires two separate 80 percent passes rather than one blended score, missing either the hazmat side or the tank vehicle side means you do not get the combined endorsement - there is no averaging between the two tests.
Domain-by-Domain Quick Review
X knowledge content is organized across ten domains that blend hazardous materials regulation with tank vehicle physics and equipment operation. Here is the condensed version of each.
Domain 1: Hazardous Materials Regulations
The largest and densest domain. Covers the Hazardous Materials Table, shipping papers, marking, labeling, placarding, packaging rules, ORM-D material, hazmat accident reporting, and rules for tunnels and railroad crossings.
- Know how to read a Hazardous Materials Table entry column by column
- Memorize placarding thresholds and label pairing rules
Domain 2: Hazardous Materials Handling
Focuses on loading, segregation, and safe handling practices for regulated materials while in transit or during transfer.
- Know incompatible material segregation rules
- Understand safe loading and securement expectations
Domain 3: Operation of Emergency Equipment
Covers what emergency equipment must be carried and how it is used correctly in a hazmat/tank combination scenario.
- Know required onboard emergency equipment categories
Domain 4: Emergency Response Procedures
Tests judgment during spills, leaks, fires, or accidents involving hazardous cargo in a tank vehicle.
- Know notification and reporting obligations after an incident
Domain 5: Causes, Prevention, and Effects of Cargo Surge on Vehicle Handling
Liquid surge is unique to tank vehicles and directly affects steering and stability.
- Understand how partial loads amplify surge compared to full tanks
Domain 6: Braking Procedures for Empty, Full, and Partially Full Tanks
Braking behavior changes dramatically depending on load level and liquid movement inside the tank.
- Know why partially full tanks are the hardest condition to brake safely
Domain 7: Baffled and Compartmented Versus Non-Baffled Tank Handling
Baffles and compartments limit forward-and-back liquid movement; non-baffled tanks do not.
- Know which tank types are more prone to side-to-side surge
Domain 8: Tank Vehicle Type and Construction Differences
Covers structural differences between tank types and how construction affects handling and load response.
- Know general construction characteristics tied to stability
Domain 9: Effects of Road Grade and Curvature on Tank Vehicle Handling
Grades and curves interact with surge and high centers of gravity in tank vehicles.
- Know why speed adjustments matter more on curves with liquid cargo
Domain 10: Proper Use of Emergency Systems
Covers correct activation and operation of onboard emergency systems specific to tank vehicles.
- Know the sequence and purpose of emergency shutoff systems
For a longer walkthrough of how these ten areas map onto actual test questions, the X Exam Domains 2026: Complete Guide to All 10 Content Areas goes into more depth than a cheat sheet can.
Hazardous Materials Regulations: The Heaviest Block
Domain 1 deserves extra attention because it is explicitly the heaviest content block on the hazmat side of X. If you only have time to over-prepare for one area, make it this one.
- Hazardous Materials Table: Know how to locate the proper shipping name, hazard class, identification number, and packing group for a given material.
- Shipping papers: Know what must appear on shipping papers, where they must be kept in the cab, and how they must be presented in an emergency.
- Marking and labeling: Know the difference between package marking requirements and label requirements, and when both apply.
- Placarding: Know when placards are required based on hazard class and quantity, and how placards must be displayed on a tank vehicle.
- Packaging: Know general packaging integrity and compatibility rules for hazardous materials.
- ORM-D: Know how ORM-D materials are treated differently from fully regulated hazardous materials.
- Accident reporting: Know what triggers a hazmat incident report and the reporting timeline expectations.
- Tunnels and railroad crossings: Know restrictions on hauling hazardous materials through tunnels and required procedures at railroad crossings.
Tank Vehicle Handling Essentials
The tank vehicle side of X is shorter in question count but tests physical intuition rather than memorized tables. Four ideas repeat throughout Domains 5 through 9:
- Surge is worst when tanks are partially full. A full tank has little room for liquid to move; an empty tank has no liquid to move. Partial loads create the most forward, backward, and side-to-side motion.
- Baffled and compartmented tanks reduce forward-back surge but do not eliminate side-to-side movement, which still affects turns.
- Non-baffled tanks (like many liquid tankers) surge more freely and require more conservative braking and steering inputs.
- Grade and curvature amplify every surge effect. A curve combined with a partially full, non-baffled tank is the highest-risk handling scenario tested.
Domain 10's emergency systems content and Domain 3's emergency equipment content often get tested together, since both relate to what a driver must do - and use correctly - when something goes wrong mid-route.
Key Takeaway
If a question describes a partially full, non-baffled tank on a downhill curve, it is almost always testing your understanding of compounded surge risk, not a random handling fact.
Registration and Fee Mechanics
X is not something you "sign up for" the way you would register for a standalone certification exam. Instead, it results from a sequence tied to your CDL:
- You must already hold or be applying for a CDL through your state driver licensing agency.
- You apply for the Hazardous Materials (H) endorsement, which requires passing the hazmat knowledge test and clearing a TSA Security Threat Assessment with fingerprinting.
- You apply for the Tank Vehicle (N) endorsement, which requires passing the tank vehicle knowledge test - no TSA background check or ELDT is required for this endorsement alone.
- If you hold both H and N at the same time, your CDL is printed with the combined X code.
Since February 7, 2022, first-time H endorsement applicants must also complete hazmat entry-level driver training from a provider listed on the FMCSA Training Provider Registry before testing. This training requirement does not apply to the tank vehicle endorsement on its own. If you're unsure whether you qualify to start this process, review X Requirements 2026: Eligibility, Prerequisites & How to Qualify before scheduling anything.
Final Review Week Plan
If you're using this cheat sheet in the final stretch before test day, structure your remaining time around the two knowledge tests separately rather than blending them.
Hazmat Regulations Deep Pass
- Hazardous Materials Table lookups
- Shipping papers, marking, labeling, placarding
- ORM-D, accident reporting, tunnels/railroad crossings
Hazmat Handling and Emergency Content
- Domain 2 handling and segregation rules
- Domains 3 and 4: emergency equipment and response procedures
Tank Vehicle Physics
- Surge (Domain 5) and braking behavior (Domain 6)
- Baffled vs. non-baffled comparisons (Domain 7)
Construction, Grade, and Emergency Systems
- Tank construction differences (Domain 8)
- Grade and curvature effects (Domain 9)
- Emergency system operation (Domain 10)
Mixed Practice and Weak-Spot Review
- Run full-length practice sets covering both knowledge areas
- Re-check any domain where you're missing questions
Reinforce this schedule with realistic practice sets on the main practice test platform, since repeated exposure to how questions are phrased matters as much as knowing the raw facts. If you want a sense of how challenging candidates typically find this material, How Hard Is the X Exam? Complete Difficulty Guide 2026 breaks down the difficulty by domain.
Frequently Asked Questions
It results from two separate knowledge tests - one for the Hazardous Materials endorsement and one for the Tank Vehicle endorsement - both administered by your state driver licensing agency. The combined code appears on your CDL once you hold both endorsements.
Federal regulation 49 CFR 383.135 requires 80 percent correct on each knowledge test. There is no averaging between the hazmat and tank vehicle tests.
Yes, if you are a first-time H endorsement applicant. Since February 7, 2022, you must complete hazmat entry-level driver training from a provider on the FMCSA Training Provider Registry. The tank vehicle endorsement has no equivalent training requirement.
The hazmat knowledge test commonly has about 30 questions, and the tank vehicle knowledge test commonly has about 20 questions. State test fees vary.
Every five years, which includes completing a new TSA Security Threat Assessment as part of the renewal process.
Keep this page bookmarked as your quick-reference companion, but pair it with full domain study and consistent practice through a dedicated practice test resource so the facts above turn into reliable exam performance rather than last-minute cramming.