When must the on-board PTC apparatus be tested?

The requirement for testing the on-board Positive Train Control (PTC) apparatus within the previous 24-hour period ensures that the system is functioning properly and can fulfill its safety obligations. This timeframe allows for regular monitoring and ensures that any potential issues are identified and resolved promptly, before they can affect train operations or safety.

Regular checks within this 24-hour window help maintain operational readiness and compliance with regulatory standards. It acknowledges the dynamic nature of rail operations, where conditions can change frequently, and reinforces the importance of having PTC systems that are consistently operational and reliable. The emphasis on testing within this specific timeframe ensures that, on any given day, the train is being operated with a tested and verified PTC system, enhancing overall safety on the rail network.

The other options imply testing requirements that do not align with the best practices for ensuring ongoing safety and operational integrity. For instance, testing before each trip may not be practical, and the approach of only testing when malfunctions occur does not promote proactive safety measures.