Under what condition can a train change direction within automatic interlocking limits?

The correct answer focuses on the operational rules governing the movement of trains within automatic interlocking limits. A train can change direction within these limits if it continuously occupies at least one car length of the interlocking limits. This condition is crucial because it ensures that the train's presence is registered and that the interlocking system can maintain safe movements by recognizing that the train is actively occupying the track.

Maintaining the continuous occupation of at least one car length helps prevent miscommunication or confusion regarding track occupancy which could lead to potential conflicts with other trains or signals. This rule allows for a controlled and safe environment for direction changes, as it keeps the train within the known bounds of the interlocking system.

The other options, while they might seem reasonable in a different context, do not meet the specific operational requirement established for automatic interlocking systems. For instance, stopping first is not necessary as the train can shift direction while in motion—as long as the critical condition of continuous track occupation is met. Dispatcher approval, while important in many instances, is not a prerequisite for direction changes within the defined interlocking limits, and crew agreement is not a standard operational requirement under these circumstances.