How should the air brake system be charged before conducting a test for a transfer train?

The air brake system must be charged to at least 60 psi to ensure that there is sufficient pressure to operate the brakes effectively during testing. This minimum pressure is crucial for demonstrating that the brake system is functioning correctly and can provide the necessary stopping power when needed. Proper charging of the air brake system enhances safety by ensuring all components are adequately pressurized and ready for operational testing. Charging to this level allows for the effective assessment of brake responsiveness and integrity, which is vital for the overall safety of the train during its journey. Other pressure levels, while potentially relevant, do not meet the minimum requirement necessary for a reliable brake test.