Where does time apply on single track?

Time on single track applies at the first switch where an opposing train clears because this is the point at which the movement of trains on the single track can safely resume after one train has cleared the way for another. In other words, it is the first location that indicates the end of the necessity for a hold or wait for the opposing train.

This context is important because trains must be coordinated to prevent collisions on single-track sections. Once one train has cleared the first switch, it allows for the next train to proceed safely, and therefore, time is established at that point for operational clarity and efficiency.

While other locations might be relevant to train movements, they do not signify the point at which time applies for the safe passage of trains in the context of single-track operations. Each of the other options lacks the specific function of marking the point where communication of clear passage is formally recognized and time is applied for movement.