Which of the following must occur if communication fails during the dispatch process?

When communication failures occur during the dispatch process, it's essential to prioritize safety and reliability. The correct response indicates that no train can proceed until communication is restored. This is critical because effective communication is vital for coordinating train movements, ensuring that all trains are aware of their surroundings, and avoiding potential collisions or accidents.

If communication is lost, dispatchers may not be able to relay necessary information regarding track conditions, signal statuses, or other operational updates that could affect the safety of train operations. Preventing any train from proceeding without restored communication helps to mitigate risks and maintain operational integrity, aligning with safety protocols in railroad operations.

The other options imply varying degrees of operational continuity without communication, which contradicts safety best practices. For example, allowing trains to continue if visually clear may lead to misjudgments about track conditions or the presence of other trains. Informing passengers to remain calm might be part of a contingency plan but does not address the primary concern about train safety and movement. Lastly, imposing a predetermined wait time for updates without communication does not adequately resolve the failure and could lead to dangerous situations. Thus, ensuring that no trains proceed without communication is the safest and most responsible course of action.