The Commercial Driver’s License (CDL) permit test, formally known as the Commercial Learner’s Permit (CLP) knowledge test, is the initial step for anyone seeking to operate a commercial motor vehicle. Passing this written examination is mandatory to receive a CLP, which allows applicants to begin supervised, behind-the-wheel training. The test evaluates a candidate’s theoretical understanding of federal and state regulations, vehicle operation, and safety procedures.
General Knowledge Requirements
The General Knowledge test is the foundational assessment required of every CDL applicant, regardless of the vehicle class (A, B, or C) or any specialized endorsements they pursue. This comprehensive test covers a broad spectrum of information necessary for safe commercial vehicle operation. Content focuses on safe driving practices, including managing speed based on vehicle weight and road conditions, maintaining proper space, and developing hazard perception to anticipate problems.
Test questions also address fundamental vehicle control, such as correct gear shifting techniques when navigating hills or curves, and safe procedures for turning and backing. Applicants must demonstrate knowledge of basic traffic laws specific to commercial vehicles, the proper use of mirrors, and techniques to overcome limited visibility associated with blind spots. A significant portion of the test covers pre-trip inspection procedures, detailing components that must be checked—like tire condition, brake systems, and steering linkage—to ensure the vehicle is safe to operate.
The test also covers safety and emergency protocols, including actions to take during a vehicle fire, how to manage a vehicle skid, and procedures for reporting an accident. Candidates are also tested on the principles of safely transporting cargo, which includes understanding weight distribution, securing loads, and recognizing maximum weight limits and axle weight restrictions.
Core Vehicle Configuration Tests
Beyond the General Knowledge requirement, applicants must pass additional knowledge tests based on the specific mechanical configurations of the vehicle they intend to operate. These tests are distinct from the General Knowledge portion and are required to remove restrictions on the CDL, allowing the operation of vehicles with certain features. The Air Brakes test and the Combination Vehicles test fall into this category, focusing on specialized knowledge for these systems and vehicle types.
The Air Brakes test assesses understanding of the compressed air braking system. This includes knowledge of the system’s three main components—the service brake, parking brake, and emergency brake—and how they interact. Candidates must know specific inspection procedures, such as testing the low air pressure warning signal (which must activate at or above 60 psi) and performing the air loss rate test (which must not exceed 3 psi in one minute for a straight truck or bus with the engine off and brakes released). Knowledge of system components like the air compressor, governor, and safety relief valve is also covered to ensure the driver can identify and react to malfunctions.
The Combination Vehicles test is required for Class A CDLs, which involve a tractor and one or more trailers. This test focuses on the unique operational challenges of linking and managing multiple units, which significantly affects vehicle handling. Topics include the precise coupling and uncoupling procedures for connecting the tractor to the trailer, including checking the fifth wheel locking jaws and airlines. The test also assesses knowledge of controlling trailer skids, managing the effects of off-tracking (where the rear wheels follow a shorter path than the front wheels in a turn), and the risk of rollovers.
Specialized Endorsement Content
Specialized endorsements are additional certifications requiring separate knowledge tests, enabling a commercial driver to transport specific types of cargo or passengers. These tests focus on unique regulations and handling procedures. The Passenger (P) endorsement, required for transporting 16 or more people, covers safe loading and unloading procedures, communication with passengers, and the use of emergency exits.
The School Bus (S) endorsement requires a rigorous test that includes specific procedures for safely managing students, using external mirror systems to monitor the danger zone around the bus, and complying with laws regarding railroad crossings. The Tanker (N) endorsement focuses on the dynamics of transporting bulk liquids or gases, including understanding the effects of liquid surge and slosh on vehicle stability and the importance of bulkheads.
The Hazardous Materials (H) endorsement requires detailed knowledge of federal regulations for transporting materials that pose a risk to health, safety, or property. This content includes:
- The nine classes of hazardous materials.
- The proper use and placement of hazard placards.
- The requirements for shipping papers.
- Emergency response procedures in the event of a spill or accident.