1.2 Endorsement Codes, Knowledge Testing & Licensing Rules (N, H, X)

Once you know a vehicle is a tank vehicle, the next question is what has to appear on your license and how you earn it. The tank endorsement is one of the simplest to add, but the combined hazmat version brings extra federal steps. Mixing up those rules is a common source of wrong answers and wasted trips to the licensing office.

Endorsement Codes (49 CFR 383.153)

States must print federal endorsement codes on the CDL:

Under 49 CFR 383.93(c), the tank vehicle endorsement requires a knowledge test. It has no skills test of its own. If you already hold a Class A or B CDL, you add N by passing the tank knowledge test and paying your state's fee.

When N, H, or X Applies

Two questions decide the code:

1. Is the vehicle a tank vehicle? (Section 1.1)
2. Is the cargo a hazardous material that requires a hazmat endorsement?

Under 49 CFR 383.153, a driver who holds both the tank vehicle and hazardous materials endorsements has them shown as the single code X. Either way, you need both qualifications.

The Tank Vehicle Knowledge Test

States build CDL knowledge tests under 49 CFR 383.133, which requires:

• Questions drawn from an FMCSA pre-approved pool comparable to the AAMVA 2005 CDL Test System.
• A set number of questions from each knowledge area, with 25% new questions in each new test version.
• Repeated questions moved to a new position, and the three possible responses put in a different order. The federal rule assumes three answer choices per question, even though practice quizzes in this guide use four.
• A different version of the test when you retake a failed test.

Passing standard (49 CFR 383.135): at least 80% correct. Each state sets the number of questions on its tank test, along with fees, scheduling, and retest waiting periods, so check your state's CDL manual or licensing agency.

What the test covers

49 CFR 383.119 lists what you must know for the tank vehicle endorsement:

1. Causes, prevention, and effects of cargo surge on vehicle handling
2. Proper braking when the vehicle is empty, full, and partially full
3. Handling differences between baffled or compartmented tanks and non-baffled tanks
4. Differences in tank vehicle type and construction
5. Differences in cargo surge for liquids of varying product densities
6. Effects of road grade and curvature with filled, half-filled, and empty tanks
7. Proper use of emergency systems
8. For drivers of DOT specification tank vehicles, retest and marking requirements
9. Operating practices and procedures not otherwise specified

The AAMVA model manual puts this in Section 8, Tank Vehicles, and tells tank applicants to also study the general driving, air brake, and combination vehicle sections. The current manual text also refers applicants to Section 9 (hazardous materials). This guide's chapters follow the 383.119 list.

Entry-Level Driver Training Does Not Apply to N

The entry-level driver training (ELDT) rule took effect on February 7, 2022. Under 49 CFR 380.609 it applies to:

• First-time Class A or Class B CDL applicants and upgrades to Class A or B
• First-time passenger (P), school bus (S), and hazardous materials (H) endorsement applicants

The tank vehicle (N) endorsement is not on that list. A Class A driver adding only N does not need a Training Provider Registry course. A driver seeking X needs ELDT for the H portion only.

Learner's Permit Rules (49 CFR 383.25)

Only three endorsements may appear on a commercial learner's permit (CLP): P, S, and N. For N:

• The CLP holder must have passed the N knowledge test.
• The CLP holder may only operate an empty tank vehicle.
• The CLP holder may not operate any tank vehicle that previously contained hazardous materials and has not been purged of any residue.
• A CLP holder may not operate a CMV transporting hazardous materials at all.

The AAMVA manual describes this as the CLP restriction "No cargo in CMV tank vehicle."

H and X: The Extra Federal Steps

The hazardous materials portion adds requirements that N alone does not have:

• Security threat assessment: the Transportation Security Administration (TSA) must complete a background check, including fingerprints, before a state issues or renews H (49 CFR 383.141 and 49 CFR Part 1572).
• Hazmat knowledge test at renewal: a driver who wants to keep H must pass the hazardous materials test again when renewing the CDL (49 CFR 383.73).
• ELDT: required the first time you obtain H.

A CDL itself may be valid for no more than 8 years (49 CFR 383.73). N normally stays on the license through renewals, but retest rules for renewals are set by each state.

Driving Without the Endorsement

Under 49 CFR 383.37, an employer may not knowingly allow a driver to operate a CMV without a CDL of the proper class and endorsements. Roadside inspectors check the license against the vehicle and cargo, so an N-required load with no N or X on the license is a violation for both driver and carrier.