What is the term for a segment of track within defined limits where trains may operate only as authorized?

The correct term for a segment of track within defined limits where trains may operate only as authorized is "Working Limits." This term is critical in railroad operations as it establishes a controlled area on the track, often used for maintenance, construction, or safety reasons, where the normal rules of train operation are modified to ensure safety. Authorized personnel can enter these limits, and it often requires strict adherence to specific protocols to prevent unauthorized access and ensure the safety of workers and trains in the area.

Other terms provided do not accurately describe this specific concept. A "Yard" refers to an area where trains are stored or assembled but does not necessarily restrict train operation as specified. "Yard Track" is simply a type of track within a yard designated for storing or moving rolling stock and does not imply restricted operation as in working limits. An "Alerter" is a safety device used in locomotives to alert the operator and ensure continuous attention while driving, but it does not pertain to track segments or operation authority.