What is the main requirement to utilize Form D?

The main requirement to utilize Form D is that it must remain in effect until fulfilled or canceled. This characteristic is crucial because Form D serves as an official communication tool for train movements, and its effectiveness depends on ensuring that it remains valid for the duration of its intended purpose. If it were to expire or be nullified before the actions it governs are completed or formally canceled, it could lead to confusion or unsafe conditions in train operations.

The stipulation that the Form D must stay in effect emphasizes the importance of clear communication and operational integrity in the rail system. This provision ensures that all personnel involved understand the current operational parameters and can act accordingly until the form's conditions are no longer in force.

While signing by the dispatcher, stating the train's origin, and requiring approval from the RWIC are important elements in the overall use and management of Form D, they do not capture the primary operational requirement that ensures the document's effectiveness and reliability throughout the entirety of its application.