During a Class III Brake Test, the brakes must apply in response to a reduction of how many PSI in the brake pipe?

During a Class III Brake Test, a reduction of 20 PSI in the brake pipe is required for the brakes to apply. This specific pressure drop is established as a standard for ensuring that the braking system is functioning correctly and can reliably respond to signal changes. The 20 PSI reduction represents a threshold that indicates a sufficient level of pressure change to activate the brakes and assure that they will engage properly in various operating conditions.

Understanding this standard is critical for both safety and regulatory compliance within rail operations. By applying brakes in response to this specific reduction, operators can demonstrate that the entire braking system is operational, which is vital for maintaining safety on the tracks.