How is movement on a main track authorized in Automatic Block Signal (ABS) territory?

Movement on a main track in Automatic Block Signal (ABS) territory is authorized by ABS signals indicating track conditions. In this signaling system, signals are strategically placed along the track to communicate the status of the block ahead to train crews. These signals may indicate whether a block is clear, occupied, or if speed restrictions are in place. This method enhances safety and efficiency by providing real-time information about the track and its conditions, ensuring that trains can operate safely without collisions.

The other options lack the mechanism required for effective and safe operation in this type of territory. GPS tracking systems are useful for location tracking but do not directly indicate track conditions. Verbal instructions, while valid in certain situations, do not provide the standardized and reliable means of authorization necessary for main track movements. Freight routing documents, likewise, are logistical tools rather than direct authorizations for movement on the track. Thus, the primary mechanism for authorizing movement in ABS territory relies on the signals that are integral to the signaling system.