What must trains or engines do when they observe an approaching train?

When trains or engines observe an approaching train, the proper action is to give way as soon as possible. This is essential in maintaining safety on the tracks, as it helps prevent potential collisions and allows for smooth rail operations. Railroads operate under strict safety protocols, and yielding to the right-of-way is crucial for avoiding accidents.

While other options, such as continuing at normal speed, signaling loudly, or switching tracks, might seem relevant in different contexts, they do not prioritize safety in the same way giving way does. Continuing at normal speed could lead to dangerous situations if the trains come too close. Signaling the approach of a train, although important, is not sufficient action by itself if there is a risk of collision. Switching tracks may also not always be possible or safe depending on the situation and the configuration of the tracks. Therefore, the most appropriate and responsible action is to give way as soon as possible when encountering an approaching train.