When governed by Automatic Block Signal rules, what must happen before re-entering a block?

Before re-entering a block governed by Automatic Block Signal rules, it is essential to verify the signal indication or obtain permission. This step is crucial because it ensures the safety of operations by confirming that the block is clear and that it is safe to proceed. The signals provide vital information about the status of the block ahead, such as whether it is occupied or if it is safe for a train to enter.

Accurately interpreting the signals helps prevent accidents that could occur from entering an occupied block or proceeding without the necessary authority. By prioritizing the verification of signal indications or permission, a train crew maintains compliance with safety protocols that govern train operations in a modern railroad environment.