In emergency mode, how must parking brakes perform on air brake systems?

In emergency mode, parking brakes on air brake systems are required to exert a retarding force equal to twenty-eight percent of the gross axle rating. This specification ensures that the vehicle can come to a safe stop even under adverse conditions, such as a failure of the primary braking system.

The twenty-eight percent requirement is designed to provide adequate stopping power, particularly in emergencies where the driver may need to rely solely on the parking brake. This level of force is important as it helps maintain control of the vehicle while preventing it from rolling, especially on inclines or during emergency maneuvers. By having a robust standard like this, it reinforces safety features that are critical in school bus operations, protecting both the passengers and the driver.

Understanding this aspect is vital for technicians as they work with braking systems to ensure compliance with safety regulations and optimal vehicle performance.