In an air brake test, what is the required brake pipe pressure reduction to apply the brakes after notification?

In an air brake test, a brake pipe pressure reduction of 20 psi is necessary to effectively apply the brakes after notification. This specific pressure reduction is critical for ensuring that the air brake system has sufficient force to engage the brakes and stop the train safely.

The 20 psi reduction is a standard set by industry practices and regulations to guarantee that the braking mechanism is responsive and reliable. When this reduction occurs, it triggers the application of the brakes across the train, alerting the entire system to begin the stopping process. This level of reduction ensures that there is enough air pressure differential to actuate the brake cylinders effectively.

Other options, while they represent different psi reductions, do not meet the established requirements for effective brake application in this context. The choice of 20 psi balances the need for a prompt brake application with the technical capabilities of the brake system, ensuring safe operations on the railroads.