What must be done before authorizing two opposing movements in a controlled siding?

Before authorizing two opposing movements in a controlled siding, it is essential to notify the engineers of each movement. This is crucial because it ensures that both train crews are fully aware of the situation and can operate their trains safely and effectively. Communication between the dispatchers and the engineers is vital to maintain awareness of potential hazards, coordinate actions, and prevent accidents resulting from miscommunication.

Engaging the engineers helps them to be prepared for the opposing movement, allowing them to adjust their operations as necessary to ensure safe passage. This level of coordination is a critical safety protocol in railway operations, and without it, the risk of collisions or derailments significantly increases.

While informing the dispatchers is also important, as they will coordinate the overall traffic and safety, the direct notification to the engineers stands out as necessary for real-time operational awareness and safety. Other options, such as waiting for an operational briefing or contacting railway police, do not directly address the immediate need for communication between the trains involved in the opposing movements.