Which procedure must be followed immediately after a train separation?

Following a train separation, it is crucial to secure the detached portions using the Secondary Securement Procedure. This step is fundamental to ensure that any cars that have separated do not move unexpectedly, which could result in hazardous situations on the track. The Secondary Securement Procedure involves applying brakes and using chocks or blocks to prevent movement, effectively mitigating risks that could lead to accidents or further incidents.

While inspecting the entire train, ensuring proper documentation, and checking passenger safety are all important aspects of train operations, they are not immediate actions that directly address the immediate concern of securing a detached portion of the train. The priority after a separation is to stabilize the condition to prevent additional dangers, making secondary securement the most critical step in this context.