Air Brakes
This endorsement is required for driving a vehicle with air brakes. To receive this endorsement, applicants must pass a written test. The test consists of 25 multiple choice questions. Each question has three answer choices. To pass, the applicant must answer at least 20 questions correctly. Test questions come from the Idaho Commercial Driver’s License Manual. Questions come from the chapter covering: Air Brakes. The Air Brakes endorsement may be used with the Class A, B or C CDL.
Number of Question
Passing Score
19. What kind of force do emergency brakes use?
Explanation
Air brakes are really three different braking systems: the service brake, the parking brake, and the emergency brake. Emergency and parking brakes are applied with mechanical force.
20. An air compressor governor will stop the compressor from pumping air once the air tanks have an air pressure level of:
Explanation
An air compressor governor will stop the compressor from pumping air once the air tanks are at an air pressure level of 125 psi. This air pressure level is referred to as the "cut-out" level.
21. A safety valve is set to open at ____ pounds per square inch (psi).
Explanation
The safety valve protects air tanks and the rest of an air brake system from accumulating too much air pressure. The safety valve is usually set to open at 150 psi.
22. If you are braking on dry pavement while traveling at 55 mph, how much distance will brake lag add to your overall stopping distance?
Explanation
The total stopping distance for vehicles equipped with air brakes is made up of four factors: perception distance, reaction distance, brake lag distance, and braking distance. When braking at a speed of 55 mph while driving on dry pavement, the brake lag can add around 32 feet to the vehicle's total stopping distance.
23. Brakes may get out of adjustment:
Explanation
Brakes can get out of adjustment quickly, especially if they are used to the point of overheating. Brake adjustment should be checked frequently.
24. What do air brakes use to make the brakes work?
Explanation
Many large CMVs are equipped with air brakes. An air braking system uses compressed air to operate.
25. An emergency brake must be controlled by:
Explanation
