A commercial driver's license on its own authorizes you to operate a specific class of commercial motor vehicle. But many commercial driving jobs require more than a base CDL — they require endorsements. These are add-ons to your CDL that authorize you to haul certain cargo, operate specialized equipment, or carry passengers. Without the right endorsement, driving that vehicle type is illegal, regardless of your CDL class.
There are seven federally recognized CDL endorsement types. While the federal government establishes the framework, states administer the testing and issuance — so requirements, fees, and procedures vary.
An endorsement appears as a letter code on your physical CDL. Employers, law enforcement, and regulatory agencies use those codes to verify you're authorized for a specific vehicle or cargo type. Some jobs won't hire without them. Some insurance carriers won't cover drivers who lack the correct endorsement for a given haul.
Endorsements typically require passing an additional knowledge test, a skills test, or both — depending on the endorsement type. Some also carry ongoing requirements like medical certification or background checks.
| Code | Endorsement | What It Covers |
|---|---|---|
| H | Hazardous Materials | Transporting hazmat cargo regulated under federal law |
| N | Tank Vehicle | Operating vehicles designed to carry liquid or gaseous materials in tanks |
| P | Passenger | Driving vehicles designed to transport 16 or more passengers (including the driver) |
| S | School Bus | Operating a school bus to transport pre-K through 12th grade students |
| T | Double/Triple Trailers | Pulling double or triple trailer combinations |
| X | Combination Tank + Hazmat | Tanks carrying hazardous materials (combines H and N) |
| L | Air Brakes (Restriction Removal) | Not a traditional endorsement — removing an air brake restriction earned during CDL testing |
The X endorsement isn't a separate test — it reflects that a driver holds both the H and N endorsements and regularly operates tankers carrying hazmat cargo.
The hazmat endorsement is the most federally regulated of all seven. To obtain it, drivers must pass a Transportation Security Administration (TSA) background check in addition to a knowledge test. This check screens for disqualifying criminal history under federal security threat assessment rules.
The H endorsement must be renewed periodically, and the TSA background check recurs at renewal. Drivers transporting certain types of hazmat also need a hazmat placard displayed on the vehicle, and cargo documentation must match what's being hauled.
Tank vehicles carry liquids or gases in permanently or temporarily attached tanks. The N endorsement requires a knowledge test focused on liquid surge, center of gravity, and handling characteristics unique to tank vehicles. This endorsement matters for fuel haulers, liquid food transport, and chemical carriers.
The passenger endorsement authorizes driving vehicles built to transport 16 or more people, including the driver. This covers charter buses, transit buses, and similar configurations. It requires both a knowledge test and a skills test performed in an actual passenger vehicle. Background checks are required in many states due to the nature of passenger transport.
The school bus endorsement builds on the P endorsement — drivers typically need both. The S endorsement adds requirements specific to school bus operations: loading and unloading procedures, railroad crossing protocols, and emergency exit management. Most states require a criminal background check as part of the S endorsement process, given that drivers work with minors.
This endorsement authorizes pulling two or three trailers in combination. It requires a knowledge test but generally no separate skills test in most states — though this varies. Doubles and triples are common in freight and logistics, and the endorsement covers the unique handling, coupling, and braking dynamics involved.
The X endorsement simply indicates a driver holds both H and N endorsements and regularly operates a tanker carrying hazardous materials. It doesn't involve separate testing beyond what H and N each require. It's reflected on the CDL as a combined designation.
Technically a restriction removal rather than a true endorsement, the L code matters practically. If a driver fails or skips the air brake component of CDL testing, an air brake restriction is placed on their license. Removing it — earning the L — requires demonstrating air brake proficiency. Many commercial vehicles use air brakes, so this restriction can significantly limit job eligibility.
Several factors affect how endorsements work in practice:
For most endorsements, testing involves a written knowledge exam administered at the state DMV or a third-party testing site. Passenger and school bus endorsements typically also require a skills or road test in the appropriate vehicle type. Hazmat requires a TSA background check that runs parallel to the state testing process.
Scores required to pass, number of questions, retake policies, and waiting periods between attempts all differ by state.
The seven endorsement types are federally defined and consistent across states — but how your state tests for them, what it charges, when they expire, and what disqualifies a driver is determined locally. Your CDL class, the type of commercial driving you're pursuing, and your state's specific DMV procedures are what turn the federal framework into your actual licensing path.