What type of track is designated in the Special Instructions and where movements are controlled by a block signal system?

The correct answer reflects the definition and functionality of a main track within the context of railroad operations. A main track is specifically designated for the movement of trains and is enforced by standard signal systems that control and manage train movements according to established rules. The block signal system plays a critical role in maintaining safe distances between trains, preventing collisions, and ensuring efficient traffic flow along the railway.

In contrast, non-controlled tracks typically do not have the same level of supervision and may not utilize a block signal system, which makes them less regulated for train movements. Yard tracks are primarily used for storing, assembling, and switching trains rather than for through traffic, meaning they are not typically under the same signaling protocols as main tracks. Working limits refer to specific areas of track designated for maintenance or repairs and are also not governed by standard block signal operating procedures that apply to main tracks. Understanding these distinctions is essential for locomotive engineers in ensuring safe and efficient train operations.