CDL Endorsements — All Eight Federal Knowledge Tests
The Federal Motor Carrier Safety Administration defines eight CDL knowledge tests. Every commercial driver in the United States passes the General Knowledge test, then adds endorsement tests for the vehicles and cargo they intend to operate.
General Knowledge
50 questions on the official test · 40 correct to pass.
The General Knowledge test covers safe vehicle inspection, basic vehicle control, shifting gears, communicating, controlling speed, controlling distance, seeing hazards, distracted driving, aggressive drivers, communicat…
AIRAir Brakes
25 questions on the official test · 20 correct to pass.
The Air Brakes test covers air brake system parts (compressor, governor, reservoirs, drain valves, alcohol evaporator, safety valve, brake pedal, foundation brakes), dual air brake systems, inspecting air brakes, using a…
COMBOCombination Vehicles
20 questions on the official test · 16 correct to pass.
The Combination Vehicles test covers driving combination vehicles safely, combination vehicle air brakes, antilock brake systems, coupling and uncoupling, and inspecting a combination vehicle. Combination vehicles are us…
HAZHazardous Materials
30 questions on the official test · 24 correct to pass.
The Hazardous Materials (HazMat) test covers the rules for transporting materials that pose a risk to health, safety, and property. Topics include the hazardous materials table, shipping papers, marking, labeling, placar…
TANKTank Vehicles
20 questions on the official test · 16 correct to pass.
The Tank Vehicles test covers inspecting tank vehicles, driving tank vehicles, surge and liquid movement, baffled and unbaffled tanks, outage, and safe driving rules unique to large liquid loads. Tank vehicles handle ver…
DOUBLESDoubles and Triples
20 questions on the official test · 16 correct to pass.
The Doubles and Triples test covers pulling double and triple trailers, coupling and uncoupling, inspecting doubles and triples, antilock brake systems, and safe driving with multiple trailers. Doubles and triples are mo…
PASSPassenger Transport
20 questions on the official test · 16 correct to pass.
The Passenger Transport test covers the safe operation of buses and other vehicles designed to transport 16 or more passengers including the driver. Topics include vehicle inspection, loading and trip start, on the road,…
SCHOOLSchool Bus
20 questions on the official test · 16 correct to pass.
The School Bus test covers danger zones and use of mirrors, loading and unloading, emergency exit and evacuation, railroad-highway grade crossings, student management, antilock brake systems, and special safety considera…
Choosing the right endorsements
The right combination of CDL endorsements depends on what you'll be driving and what you'll be hauling. Drivers usually start with General Knowledge and Combination Vehicles to qualify for tractor-trailer work, then add Air Brakes if their vehicle is air-equipped. From there, specialty endorsements open additional jobs:
- HazMat (H) opens placarded chemical, fuel, and explosives transport — a higher-paying lane that requires a TSA background check.
- Tank (N) is required for any vehicle hauling 1,000+ gallons of liquid or gaseous cargo.
- Doubles/Triples (T) opens LTL work pulling more than one trailer.
- Passenger (P) is required for any bus designed to carry 16 or more passengers.
- School Bus (S) requires both Passenger and School Bus endorsements and additional state background checks.
Many drivers eventually combine endorsements: a Tank + HazMat combination opens tanker work hauling fuel, and Doubles/Triples + HazMat opens long-haul LTL hazmat work. Each combination lets you respond to a different segment of the freight market.
What's on each test
| Endorsement | Code | Questions | Required to pass | Required for |
|---|---|---|---|---|
| General Knowledge | GENERAL | 50 | 40 | All CDL applicants (Class A, B, and C) |
| Air Brakes | AIR | 25 | 20 | Vehicles equipped with air brake systems |
| Combination Vehicles | COMBO | 20 | 16 | Class A CDL (tractor-trailer combinations) |
| Hazardous Materials | HAZ | 30 | 24 | Drivers transporting placarded hazardous materials |
| Tank Vehicles | TANK | 20 | 16 | Vehicles with liquid or gaseous tanks ≥1,000 gallons |
| Doubles and Triples | DOUBLES | 20 | 16 | Drivers pulling more than one trailer |
| Passenger Transport | PASS | 20 | 16 | Drivers of vehicles designed for 16+ passengers |
| School Bus | SCHOOL | 20 | 16 | Drivers operating a school bus |