CDL Endorsements Explained: H, N, T, P, S, and X

The six federal CDL endorsements in one table

An endorsement sits on top of your license class (A, B, or C). Federal rules list the codes in 49 CFR 383.153 and the tests in 383.93. For a 2027 applicant, the list, the tests, and the learner's permit limits below read the same in the eCFR as of October 26, 2026, with no change published or proposed.

Three federal definitions in 49 CFR 383.5 decide who needs which endorsement:

• Tank vehicle: a CMV built to carry liquids or gases in a tank or tanks of more than 119 gallons each and 1,000 gallons or more in total, attached permanently or temporarily. The cargo does not have to be hazardous.
• Hazardous materials: material that must be placarded under 49 CFR Part 172, Subpart F, or any amount of a listed select agent or toxin.
• School bus: a CMV carrying pre-primary, primary, or secondary students between home and school or to school events. It does not include for-hire motor carrier operations.

How endorsements pair with CDL Class A, B, and C

• P and S follow the bus you test in. The P skills test must be taken in a passenger vehicle of the group you will drive (383.117(b)), and the S test in a school bus of that group (383.123(a)(3)). Testing in a smaller bus brings an M or N restriction.
• T assumes a combination vehicle. Doubles and triples are combination rigs, so the T test builds on combination knowledge. Washington's guide tells doubles and triples applicants to study its air brake and combination chapters too.
• H and N follow the cargo, not the class. A Class A, B, or C driver may need either one. Group C exists only for vehicles designed to carry 16 or more people, including the driver, or vehicles hauling hazardous materials (383.91(a)(3)). So a Class C plan starts with the matching endorsement: P or S for passengers, H for hazardous materials.
• A higher class covers lower ones, with the right endorsements. A Group A driver may drive Group B and C vehicles, but only with the endorsements those vehicles need (383.91(c)).

The X endorsement: tank plus hazardous materials

X is a combined code, not a separate subject. A driver who qualifies for both N and H gets X on the license (383.153(a)(9)(v)). The typical case is a cargo tank carrying a placarded hazardous liquid: the tank makes it a tank vehicle, and the placards make it a hazardous materials load. X brings everything H does, including the TSA assessment and its renewal cycle. Tank and HazMat practice are both part of the endorsement coverage planned for full CDL prep.

Do not confuse it with the X on a learner's permit. On a CLP, X is a restriction code meaning no cargo in a CMV tank vehicle (383.153(b)(2)(ix)(B)). The letter N is reused the same way: on the endorsement list N means tank vehicle, but as a restriction code N means no Class A or B passenger vehicle.

Which CDL endorsement does this job need?

The jobs below are illustrations. Your state and employer confirm the exact requirement.

What the endorsement knowledge tests cover

Federal rules set each test's topics. In brief:

• T (383.115): assembling and hooking up the units, where the heaviest trailer goes, handling and stability, and the traffic problems long rigs cause. See the doubles and triples guide.
• P (383.117): loading and unloading passengers, emergency exits, fires and unruly passengers, railroad crossings and drawbridges, and braking. See the passenger endorsement guide.
• N (383.119): cargo surge, braking when empty, full, or partly full, baffled and unbaffled tanks, product density, grades and curves, and emergency systems. See the tank vehicle guide.
• H (383.121): the hazardous materials table, shipping papers, marking, labeling, placarding, packaging, handling, routes, parking, and emergency response. See the HazMat endorsement guide.
• S (383.123): loading and unloading children with stop arms, mirrors, and lights, evacuation, and railroad crossing laws. See the school bus endorsement guide.

Test length is a state choice. As checked on October 28, 2026, Washington uses 20 questions with 16 needed to pass for T, P, N, and S, and 30 questions with 24 needed for H. In Washington, T and H knowledge scores expire 180 days after you pass and cannot be extended by renewing the CLP. For the class tests that come first, see which CDL knowledge tests you need. Full CDL prep planned for launch splits its 1,650 questions across all eight CDL tests, endorsements included.

The HazMat endorsement's extra federal steps

H is the only endorsement with a federal security check. A state may not issue, renew, upgrade, or transfer it until TSA finds that you pose no security threat, or unless you hold a valid TWIC (383.141). States must renew H every five years or less, even though the CDL itself can last up to eight. First-time H applicants also complete a theory-only ELDT course before the knowledge test. TSA's fee for new and renewing applicants rose to $88.25 on October 1, 2026, which is what a 2027 applicant should expect to pay unless TSA announces another change. The HazMat guide has the full sequence.

Endorsement tests are not in the free CDL practice set

Passy's free CDL practice questions cover General Knowledge, Air Brakes, and Combination Vehicles only. They contain no endorsement items, so they say nothing about your readiness for the T, P, N, H, X, or S tests. For those, study the endorsement chapters of your state's CDL manual, and use the free study planner, which lets you add each endorsement test you still need. At launch, full CDL prep adds practice for all five endorsement tests, one test at a time or mixed, with 206 questions and 70 flashcards planned for each.