What effect does reducing brake pipe pressure have during a service brake application?

Reducing brake pipe pressure during a service brake application is essential for the proper functioning of the air brake system on a train. When the brake pipe pressure decreases, it directly results in the activation of the brake valves throughout the train. This action leads to a response in the brake system, allowing more air to flow into the brake cylinders. As a consequence, the brake cylinder pressure is effectively increased, allowing the brake shoes to engage with the wheels and slow down or stop the train as desired.

By maintaining an understanding of how brake pipe pressure interacts with the overall brake system, train operators can ensure safe and efficient braking. It's key for operators to know that a decrease in brake pipe pressure serves to increase the brake cylinder pressure, which is critical for effective braking. The correct answer highlights this important relationship, demonstrating how braking operations rely on manipulating air pressures within various components of the brake system.