Final answer:
Rule 712.31 refers to a regulation for the safe operational distance that must be maintained between trains (OTE), which can vary based on the rules of the specific rail authority or company.
Step-by-step explanation:
The question appears to be related to statutes or regulations governing the operation of trains, specifically mentioning Rule 712.31. However, without additional context, it's not feasible to provide a definitive distance that 'OTE' (presumed to mean 'other trains or equipment') must maintain when following another train. This type of rule is typically established by individual railroad companies or national railway authorities to ensure safe operation distances between trains. The safe following distance may vary depending on factors like speed, track conditions, and the braking capabilities of trains.
Since the exact rule or regulation is not universally applicable and might differ between jurisdictions or rail networks, it would be important for the student to refer to the specific rulebook or operational guidelines issued by the authority or company that operates in their region or for the network in questions, such as those published by the Federal Railroad Administration (FRA) in the United States, or similar bodies internationally.