What characterizes a manual block in railway systems?

A manual block in railway systems refers to a section of track that is governed by specific rules and procedures, particularly those that require human intervention for operation and management, rather than relying on automated signaling systems. In this context, the correct response indicates that a manual block is defined by the track length between two monitored block limit signals.

These signals are placed at the beginning and end of the manual block segment, ensuring that train movements are controlled and monitored effectively. The use of block limit signals offers a safeguard to ensure trains do not enter the block until it is clear, which is crucial for maintaining safety and efficiency in rail operations.

Other choices may suggest characteristics related to automated systems or specific train types, but they do not accurately reflect the core definition of a manual block as primarily focused on the human management of track segments defined by monitored signals.