What are the critical differences in air brake testing procedures required when interchanging railcars with another railroad, and why are these differences important?

When railcars are interchanged, meaning transferred from one railroad to another, specific air brake testing procedures are required that go beyond the standard tests done within a single railroad's operations. These differences are crucial to ensure the safety and compatibility of the air brake systems across different railroads. One critical difference is the verification of brake shoe force. When interchanging cars, there's a greater emphasis on confirming that the brake shoes are applying with the correct force against the wheels. This involves visually inspecting the brake rigging to ensure all components are properly connected and adjusted, and sometimes using a brake shoe force gauge to measure the actual force being applied. This is important because variations in brake rigging maintenance standards between railroads can lead to unequal braking forces, which can cause uneven wear on wheels and ....