When is it permissible to have more than one train in a manual block at the same time?

The correct choice highlights a specific procedure that allows multiple trains to occupy a manual block. Using Form T is essential in situations where the normal operating conditions are modified to accommodate additional trains due to specific needs such as service requirements or emergency responses. Form T acts as a formal authorization to ensure that all involved parties are aware of the change and can maintain safety while managing the presence of multiple trains.

It's crucial to understand that other conditions, like authorization from the Block Operator or emergencies, while they may seem feasible, are not standard procedures for permitting multiple train occupancy in a manual block. The use of proper documentation, such as Form T, ensures that all safety protocols are followed and that there is clarity among train crews and dispatchers concerning the operational status of the block. In this context, Form T serves as a critical tool for coordinated operations and safe train movement.