What is the main characteristic of a block in a railway system?

The primary characteristic of a block in a railway system is that it is governed by signals to ensure train safety. Blocks are defined sections of track that are controlled by signaling systems to manage the flow of train traffic. This signaling ensures that only one train can occupy a block at any given time, preventing collisions and enhancing the safety of operations.

The signals associated with blocks indicate whether the block is clear or occupied, allowing train operators to proceed with caution where safe, and to stop if necessary. This system is fundamental for maintaining safe distances between trains and for effective train management on busy railway lines.

In contrast, other options refer to specific situations that do not capture the essential functioning of a block within railway operations. Blocks are not required to connect to one another, can be utilized by various types of trains—not just light engines—and are not limited to nighttime operations, demonstrating that the use and functionality of blocks extend beyond these narrower assertions.