Why might a train need to come to a complete stop?

A train may need to come to a complete stop due to a stop signal because stop signals are safety mechanisms that indicate to the train engineer that there may be an obstruction ahead, another train on the same track, or a switch that needs to be changed for safe passage. The primary function of a stop signal is to prevent collisions and ensure the safety of both the crew and the cargo by requiring the train to halt until it is safe to proceed.

While other actions, such as crew changes, routine inspections, and picking up extra cargo, may also require the train to stop, the fundamental purpose of a stop signal is to preserve safety on the tracks. Understanding and responding to signals is an essential part of a train engineer's duties to ensure proper train operations.