What does a block system consist of?

A block system is primarily defined by its structure, which consists of a block or series of consecutive blocks within specific limits. These blocks are designated sections of track that are used to manage train movements safely and efficiently. Each block can be occupied by only one train at a time, preventing collisions and ensuring a safe distance is maintained between trains.

The system's design allows for trains to be monitored and controlled effectively. By establishing these defined segments, railroads can implement signal systems that inform train crews when it is safe to proceed, when they must stop, or when they may need to slow down, ensuring orderly and safe train operations.

In contrast, the other options do not accurately represent what a block system fundamentally comprises. For instance, a method to coordinate train schedules refers more to scheduling management than to the physical structure and safety measures of a block system. Similarly, while block systems can be applied to all types of trains, including freight, they are not exclusive to freight trains. Lastly, a network of signals across various railroads describes a broader signaling system that can be in place but does not specify the block structure that is central to the block system concept.