What does the brake pedal in an air brake system control?

Answer: B — The air pressure applied to put on the brakes

In an air brake system, the brake pedal plays a crucial role in controlling the air pressure that activates the brake mechanism. When you press the brake pedal, it sends a signal to the brake system to release or apply air pressure to the brake chambers. This air pressure is then used to engage the brakes, effectively slowing down or stopping the vehicle. Understanding this function is essential for safe operation, as it illustrates how the air brake system relies on compressed air to exert the force necessary for braking. This contrasts sharply with other functions, such as controlling vehicle speed, displaying brake lights, or influencing power steering, which are unrelated to the direct function of applying brakes.