When can blocks be removed during train movements?

The process of removing blocks during train movements is crucial for ensuring safety and maintaining proper train operations. The correct answer centers on the concept that blocks cannot be removed until the movement against the current of traffic has been completed. This ensures that all potential conflicts are resolved and that it is safe to proceed with removing a block.

When trains are operating in opposing directions, particularly in scenarios where there might be limited visibility or potential for human error, it's essential to wait until the movement is fully completed before altering any block statuses. Removing a block too early could lead to unsafe situations, such as a collision or a train inadvertently entering an occupied section of track.

The other choices primarily focus on different aspects that do not align with the safety protocols outlined for block removal. It's crucial that blocks only be released once all necessary criteria indicating completion of movements are met, emphasizing overall operational safety.