CDL endorsements: which ones you need

The six letters

49 CFR 383.153 lists the endorsement codes a state may print on a CDL: T for double and triple trailers, P for passenger, N for tank vehicle, H for hazardous materials, X for a combination of the tank vehicle and hazardous materials endorsements, and S for school bus. That is six letters but only five separate subjects, because X is not its own exam. It is what the state prints when you hold both N and H.

States are allowed to add their own codes for other groupings, as long as the code is explained on the license itself. So if you see a letter that is not on that list, it is a state code, and the back of your license will tell you what it means.

What triggers each one

49 CFR 383.93 says you must hold an endorsement to operate a commercial vehicle that is a double or triple trailer combination, a passenger vehicle, a tank vehicle, a vehicle used to transport hazardous materials, or a school bus. Note that the trigger is the vehicle or the cargo, not the job title. If the truck you are handed on Monday is pulling a tanker, you need N on Monday, even if you have driven dry vans for ten years.

T — doubles and triples

A knowledge test only. 49 CFR 383.93(c)(1) requires no skills test for this one, which surprises people given how differently a set of doubles behaves.

The subjects come from 49 CFR 383.115: assembling and hooking up the units, putting the heaviest trailer in the right place, and the handling characteristics of a jointed vehicle — off-tracking, sensory feedback, oscillatory sway, rollover in steady turns and yaw stability. It also covers the problems your vehicle creates for everyone else, like slower speeds on grades, longer passing times and splash and spray.

Practice it on the doubles and triples practice test. The questions that catch people out are the trailer order ones, not the definitions.

N — tank vehicles

Also a knowledge test only, under 49 CFR 383.93(c)(3).

49 CFR 383.119 lists what you are tested on, and almost all of it is one idea seen from different angles: the liquid moves. Causes and effects of cargo surge, braking an empty tank versus a full one versus a half-full one, baffled and compartmented interiors versus smooth bore, how product density changes the surge, and what road grade and curvature do to a tank that is part full. It also covers emergency systems and, for DOT specification tanks, retest and marking requirements.

The tanker practice test is where to check whether you actually know the half-full answers, because those are the ones the real exam leans on.

H — hazardous materials

A knowledge test under 49 CFR 383.93(c)(4), and the one to start early.

The subject list in 49 CFR 383.121 is long: the hazardous materials table, shipping papers, marking, labeling, placarding, packaging, loading and unloading, cargo segregation, parking, routes, tunnels and railroad crossings, emergency equipment and emergency response.

The exam is only half of it. Under 49 CFR 383.141, a state may not issue, renew, upgrade or transfer a hazardous materials endorsement unless the Transportation Security Administration has determined that you do not pose a security risk, or you hold a valid TWIC. That is a background check you cannot speed up by studying harder, so file for it before you have finished revising rather than after. The same section requires states to renew the endorsement every five years or less, so the security screening happens at least that often, and to warn you at least 60 days before your endorsement expires.

Work through the hazmat practice test while the background check is running. The timing works in your favor for once.

X — tank and hazmat together

There is no X test. 49 CFR 383.153 describes X as the code for a combination of the tank vehicle and hazardous materials endorsements, so you earn it by passing both the N and the H exams and clearing the TSA check. It exists because hauling hazardous liquid is common enough to deserve one code instead of two.

P — passenger

The first of the two that need a skills test as well as a knowledge test, under 49 CFR 383.93(c)(2).

49 CFR 383.117 sets the knowledge topics: loading and unloading passengers, emergency exits including push-out windows, responding to fires and unruly passengers, railroad-highway grade crossings and drawbridges, and braking procedures.

The skills test is where a restriction can appear. 49 CFR 383.117(b) says you take it in a passenger vehicle of the class you want to drive, and 49 CFR 383.95(e) and (f) say that if you test in a smaller vehicle, the state prints a restriction barring you from the larger ones. Test in a Group B bus and you are restricted from Group A passenger vehicles. Test in a Group C vehicle and you are restricted from both Group A and Group B. The endorsement is still yours, but it is narrower than you might have assumed when you booked.

Start with the passenger practice test.

S — school bus

The only endorsement built on top of another one. 49 CFR 383.123 says you must first qualify for the passenger endorsement by passing its knowledge and skills tests, then pass the school bus knowledge test, then take a driving skills test in a school bus of the same vehicle group you will drive.

The school bus knowledge topics in 49 CFR 383.123(a)(2) are narrow and specific: loading and unloading children, including the stop signal devices, mirror systems and flashing lights required by state or federal law; emergency exits and evacuating passengers; and the state and federal rules for crossing railroad tracks. Two of those three are about the moments the bus is stopped, which is where the danger actually is.

The school bus practice test covers the danger zones and the crossing procedure in more detail than the general material does.

What you can add to a learner permit

Most endorsements have to wait for the full license. 49 CFR 383.93(a)(2) allows only three on a commercial learner permit: passenger, school bus and tank vehicle. Under 49 CFR 383.71(a)(8) you must have already passed the endorsement knowledge test for any of those before the permit is issued.

Even then they are limited. 49 CFR 383.153 says a permit holder with P or S may not carry passengers other than examiners, auditors, other trainees and the CDL holder supervising them, and a permit holder with N may only operate an empty tank that has been purged of any residue from hazardous materials.

Which to do first

Hazmat, if you want it at all, because the background check runs on somebody else's clock. After that, take the endorsement your first job actually needs and leave the rest. An endorsement you do not use still has to be kept current, and the hazmat one puts you back through screening every five years.

Everything above sits on top of the general knowledge exam, which every commercial driver takes whatever they intend to haul. If you are starting from nothing, begin with the general knowledge practice test and come back to the endorsements once that one is comfortable. The full list of exams is on the CDL practice test hub.