What authorization is needed for an engine to operate on the main track within yard limits?

When operating an engine on the main track within yard limits, the authorization needed is the yard limits themselves. Yard limits designate a specific area where train movements are allowed to operate under certain conditions, which differ from normal track regulations. Within these limits, crews are empowered to move trains with the understanding that specific rules apply to ensure safety and operational efficiency.

Under yard limits, trains can operate without requiring additional main track authorization as long as they adhere to the established safety protocols related to yard operations. This is particularly important in yard areas where train movements may be more frequent and variable. Therefore, the concept of yard limits serves as the governing authority for the movements of trains in that designated area.