What signals govern the use of blocks?

The correct choice indicates that block and cab signals, or interlocking signals govern the use of blocks. This is because both block signals and cab signals are essential components of a railway signaling system that ensure the safe and efficient movement of trains through defined segments of track known as blocks.

Block signals are visual indications placed alongside the track that inform engineers about the status of the block ahead—whether it is clear for passage or occupied by another train. Cab signals provide information directly to the locomotive engineer inside the cab, allowing for quick decision-making without relying solely on visual signals outside.

Interlocking signals are used in conjunction with signal control mechanisms to prevent conflicting train movements on adjacent tracks and to ensure that switches are correctly aligned for safe train passage. Thus, incorporating both block and cab signals, along with interlocking signals, creates a comprehensive safety framework that governs train movements within block sections, minimizing the risks of accidents and improving operational efficiency.

The other options are limited in scope, focusing on just one type of signal. Understanding the comprehensive role of multiple signal types is crucial for a train dispatcher's ability to maintain order and safety on the railway system.