What controls the amount of air released to the brake chambers?

The brake pedal is the primary control for regulating the amount of air released to the brake chambers in a vehicle equipped with air brakes. When the driver presses the brake pedal, it activates a series of components known as the brake system, which regulates air flow. This system uses compressed air to engage the brakes, allowing for effective stopping power. The more pressure applied to the brake pedal, the greater the amount of air released into the brake chambers, which multiplies the braking force applied to the wheels.

In this system, the brake pedal functions as a critical interface between the driver and the braking mechanisms of the vehicle. Other options, such as the steering wheel, clutch pedal, and accelerator pedal, do not have any direct role in controlling the air supply to the brakes. The steering wheel is used to navigate the vehicle, the clutch pedal is involved in shifting gears, particularly in manual transmissions, and the accelerator pedal controls the engine's throttle, impacting vehicle speed but not brake function. Thus, the brake pedal is essential for the proper functioning of air brake systems, making it the correct answer.