CDL Endorsements Explained — Air Brakes, Tanker, Hazmat & More
A clear guide to every CDL endorsement: what each one is, what its written test covers, and whether you need it.
CDL Endorsements Explained
An endorsement is an added authorization on your CDL that lets you operate certain vehicle types or carry certain cargo. Each endorsement has its own written test, and some require extra background checks.
Air Brakes (L)
Required if you’ll drive a vehicle with air brakes. This is one of the most common endorsements because most commercial trucks have air brakes. The test covers air brake system components, how they work, and what to check during your pre-trip inspection.
Many drivers get this endorsement at the same time as their general knowledge test since the skills test requires riding in a vehicle equipped with air brakes.
Tanker (N)
Required for transporting liquid or gaseous materials in bulk. The written test focuses on liquid surge — how a moving load shifts the vehicle — and on safe starting, stopping, and cornering with a partial or full load.
Hazmat (H)
Required for hauling hazardous materials. This endorsement needs a TSA background check in addition to the written test. The test covers hazard classes, placarding, emergency response, and safe loading and handling.
Passing hazmat can significantly expand your job options and earning potential.
Doubles/Triples (T)
Required for pulling double or triple trailers. The written test covers safe towing, coupling and uncoupling, and the extra space and stability challenges of multiple trailers.
Passenger (P)
Required if you’ll carry passengers, such as a motorcoach or bus driver. You’ll need a knowledge test plus a skills test in an actual passenger vehicle.
School Bus (S)
Required in addition to the Passenger endorsement to operate a school bus. The test covers student loading and unloading, emergency exits, and additional safety duties.
Do You Need One?
Only pursue endorsements that match the jobs you want — each one means more study time and, for hazmat, a background check. Start with general knowledge and air brakes, then add others as your career needs them.
Want to check your knowledge? Practice the air brakes and endorsement questions here.