What must be issued if the route to be used is diverting with Form D line 7?

When dealing with a diversion indicated by Form D line 7, it is essential to ensure that all operators are aware of any speed restrictions or other relevant operational details associated with the diversion. Form D line 1 or a Bulletin Order item provides the necessary framework to communicate specific instructions related to speed limits on the diverted route. This documentation serves to ensure the safety and efficiency of train operations during a diversion, as it helps maintain control over speeds while the train navigates through the altered path.

In this scenario, while a notification to all operators and other options may seem pertinent, they do not specifically address the critical need for clear speed-related instructions that accompany a route diversion. Therefore, issuing Form D line 1 or a Bulletin order item indicating speed is the most appropriate and correct action to take in this context. It directly supports safe operations, ensuring that all parties understand and adhere to any speed changes resulting from the diversion.