Which condition allows multiple trains or engines to occupy the same or overlapping limits in Rule 171 and 271 territories?

The correct choice highlights that trains move on a "Proceed" Authority while under specific restrictions within overlapping limits. In Rule 171 and 271 territories, the concept of overlapping limits refers to sections of track where multiple trains or engines can occupy the same area, but only under controlled conditions.

When trains are authorized with a "Proceed" Authority, it indicates they have the clearance to advance into these overlapping limits; however, the added restrictions ensure that safety and operations remain prioritized. Restrictions may include speed limitations, conditions for stopping, or requirements for communication among crews, which collectively help to manage the safe operation of trains in close proximity to one another.

This option ensures that trains can operate together under specific guidelines that mitigate risks, making it the correct answer in this context. Other selections either lack the specific safety considerations that "Proceed" Authority encompasses or offer general statements that do not reflect the necessary operational constraints.