When operating on a grade, what is the recommended brake pipe reduction for long distances?

When operating on a grade, the recommended brake pipe reduction of 15 psi or less is advised for long distances because this gradual reduction helps maintain control over the train's braking effectiveness while preventing sudden changes in air pressure that could lead to loss of control or unintentional braking reactions. A reduction of 15 psi allows for sufficient braking power to manage the train's speed on inclines, while still affording a margin of safety and the ability to adjust the braking effort as necessary throughout the descent. This technique is particularly important on longer grades, where the dynamics of the train can change significantly, and maintaining a steady braking application is crucial for safe operation. Additionally, this approach minimizes the risk of overheating the brake components and ensures compatibility with the air brake system's operational limits, making it an essential practice to ensure safety and efficiency in train handling.