In 261 territory, what must be ensured before allowing a non-shunting train into a block?

In 261 territory, allowing a non-shunting train into a block requires ensuring that blocks must protect against opposing movements. This is crucial for maintaining safety and preventing accidents on the railway. In 261 territory, signals are used to control train movements, and blocks are established to ensure that a train can occupy a specific section of track safely.

The requirement for block protection against opposing movements means that before a train can enter a block, you need to guarantee that there aren’t any trains approaching from the opposite direction that could result in a collision. This protection is typically achieved through the signaling system, which will prevent signals from displaying proceed aspects for opposing movements when a block is occupied or if a train is preparing to enter that block.

This safety measure is pivotal in maintaining safe operations in areas with potential for conflicting train movements. The other options do not address the critical need for ensuring that opposing movements are adequately controlled before allowing a train into a block, which is a fundamental principle of safe dispatching in railway operations.