What defines an absolute block in railway operations?

An absolute block is defined as a section of track where no train can enter while it is occupied. This ensures safe operation by preventing two trains from simultaneously occupying the same section of track, which could lead to collisions. The block system facilitates the safe movement of trains and is integral to railway operations, allowing for the management of train traffic in a controlled manner.

In contrast, other options do not accurately describe the concept of an absolute block. For instance, a section reserved for emergency vehicles only does not align with the fundamental purpose of a block, which is to manage train movements. Similarly, defining a block strictly for passenger or freight operations does not capture the essence of an absolute block, which applies to the prevention of train occupancy regardless of the type of service. The key aspect of an absolute block is its role in ensuring safety and operational integrity on shared railway tracks.