CDL Endorsements
There are six CDL endorsements. Five have their own knowledge test; the sixth is granted automatically when you hold two of the others. Air brakes is not an endorsement — it is a restriction you remove, which is the single most common misunderstanding about commercial licensing.
| Code | Endorsement | Knowledge test | What it covers |
|---|---|---|---|
| H | Hazardous Materials | 30 questions | Required to haul any load that must display hazmat placards — ELDT required, TSA background check |
| N | Tank Vehicles | 20 questions | Required to haul liquid or gas in bulk |
| T | Doubles and Triples | 20 questions | Required to tow two or three trailers |
| P | Passenger Transport | 20 questions | Required to carry 16 or more people including the driver — ELDT required, skills test too |
| S | School Bus | 20 questions | Required to drive a school bus — ELDT required, skills test too |
| X | Tank and Hazmat | No separate test | Granted automatically when you hold both H and N |
Which ones do you actually need?
Only the ones matching the driving you will do. Every applicant takes the general knowledge test regardless, and your licence class determines the rest — see Class A and Class B.
Three of them need training before you can even test
Hazmat, passenger and school bus all require entry-level driver training theory from a provider on the FMCSA Training Provider Registry before your first knowledge test. Hazmat additionally requires a TSA security threat assessment, and it expires every five years.
See the full CDL process, start to finish →
More CDL guides
See every CDL knowledge test and guide →
Frequently asked questions
How many CDL endorsements are there?
Six: H (hazardous materials), N (tank vehicles), T (doubles/triples), P (passenger), S (school bus) and X, which is H and N combined. Only the first five have their own test.
Is air brakes a CDL endorsement?
No — and this trips up a lot of applicants. Air brakes is a restriction removal. Skip or fail that test and an L restriction goes on your licence barring you from vehicles with full air brakes.
What is the X endorsement?
It is not a separate test. Hold both the hazmat (H) and tank vehicle (N) endorsements and your licence shows X instead of listing both.
