What action should an operator take if the train does not accelerate after adjusting the controller to multiple?

The appropriate action when a train does not accelerate after adjustments to the controller should focus on investigating potential issues with the power supply, specifically checking for a dead third rail. In rail systems where the third rail provides electrical power, it is crucial to verify that the supply is functioning properly. If the third rail is dead, the train would not receive the necessary power to accelerate, hence the operator should prioritize this check as it is directly related to the train's inability to perform as expected.

Investigating the controller mechanism could be a reasonable follow-up action but may not address the immediate concern of power availability. Notifying the control center becomes necessary after confirming the lack of power or if other systemic issues are detected. Turning off the power immediately is a drastic measure that may not be warranted at this moment, especially if the root cause may be an isolated issue with the power supply rather than a safety concern necessitating an immediate shutdown. Checking for a dead third rail should be the first step in diagnosing the situation effectively.