When approaching a signal that requires a stop, what is required to ensure proper brake functionality?

Making a brake pipe reduction in advance of the stop is essential for ensuring proper brake functionality when approaching a signal that requires a stop. This action helps to set up the air brake system so that the brakes are fully charged and ready to engage. By reducing the brake pipe pressure before reaching the signal, engineers allow the brake shoes to take effect more efficiently, enabling the train to decelerate smoothly and come to a complete stop at the required signal.

When approaching a stop indication, it's also important to maintain optimal brake performance to avoid abrupt stopping, which can cause mechanical stress and instability. A preemptive brake pipe reduction allows a smoother transition into braking, making it a critical part of safe train handling practices. This is particularly important for heavy trains that require more time to stop due to their momentum.

In contrast, increasing the throttle, sounding the horn, or keeping the speed constant do not contribute to effective braking and may lead to either insufficient stopping or unnecessary risk if the train fails to stop in time. The focus on a brake pipe reduction is a standard practice that directly relates to safe and effective train operation.