When is a track warrant considered in effect?

A track warrant is considered in effect when the crew acknowledges the "OK" time, as this acknowledgment confirms that the crew has received and understood the warrant's terms and conditions. This process is essential for ensuring clarity and safety in operations, as it establishes that the crew is aware of the track's status and any restrictions outlined in the warrant.

The acknowledgment serves as a critical communication link between the dispatcher and the crew. Without this acknowledgment, the track warrant cannot be deemed operational, which helps prevent misunderstandings that could compromise safety. This meticulous protocol is part of the broader framework of railroad operating procedures designed to maintain safety and efficiency on the tracks.

The other choices do not encapsulate this essential step. For instance, while the dispatcher may transmit the track warrant, it only becomes effective when the crew acknowledges it. Similarly, writing down the warrant does not automatically activate it, nor does receipt alone suffice—both require the crew's confirmation to ensure safe movement on the tracks.