Within yard limits, what must trains or engines obtain to use the main track?

In the context of operating within yard limits, trains or engines are required to obtain a track warrant that explicitly lists any affecting track bulletins. This process ensures that all movements within the yard are conducted safely and in compliance with any specific restrictions or conditions set forth in the bulletins. Track warrants serve as official permission from the railroad authority and provide critical information regarding the state of the track, signals, and any potential hazards.

The need for a track warrant is essential in maintaining safety protocols, especially in areas where multiple trains may operate in close proximity. The information included in the track warrant helps to mitigate risks associated with track conditions, signaling, and switch positions, ensuring that the crew is aware of and adheres to any necessary precautions during their movements.

In contrast, the other options do not meet the requirements for using the main track within yard limits. While verbal permissions and clearances might be part of operational procedures, they do not offer the formalized and comprehensive information that a track warrant provides. Additionally, relying solely on signal indications may not encompass all necessary factors impacting safe movements in a yard setting. Thus, obtaining a track warrant that includes affecting track bulletins is the correct procedure for ensuring safe and regulated train movements within yard limits.