What is the primary purpose of a low air pressure warning device on a school bus?

The primary purpose of a low air pressure warning device on a school bus is to alert the driver of insufficient brake air pressure. In a school bus, the braking system relies on compressed air to function effectively. This warning device is crucial for safety, as it helps to ensure that the brake system is operating within the required pressure limits. When the air pressure drops below a certain threshold, the warning device activates, indicating to the driver that immediate attention is needed to avoid compromising the vehicle's braking capabilities.

The functionality of this system is critical in preventing accidents or mechanical failures due to inadequate braking power. A well-informed driver can take prompt action when alerted by the low air pressure warning device, helping to maintain the safety of the bus and its passengers. Other options, such as signaling overheating brakes or engine malfunctions, do not pertain directly to air pressure and instead would involve different indicators or systems within the vehicle. Similarly, notifying passengers of a stop is unrelated to the air pressure system; it focuses on communication rather than vehicle safety mechanics.