What must be ensured before a train is admitted to a block according to Rule 316?

Before a train is allowed to enter a block, it is essential that the block is clear of any trains. This requirement is crucial for maintaining safe and efficient train operations. If a block is not clear, it poses a significant risk, including potential collisions or derailments, which could endanger both passengers and crew members.

This rule is designed to ensure that there are no obstructions within the block that could interfere with the safe passage of the incoming train. For train movements to occur safely, it must be guaranteed that the path ahead is unobstructed, thus providing the necessary clearance and allowing for appropriate operation speeds and stopping distances as needed.

The other options might relate to various operational protocols or conditions but do not specifically address the primary safety concern outlined in Rule 316 of ensuring that the block is clear before admitting a train.