What must a train do before transitioning into Release mode?

Before transitioning into Release mode, the train must come to a complete stop. This requirement is critical for ensuring the safety and control of the train during the transition. Release mode typically involves disengaging the train's brakes and allowing it to move freely, which could be hazardous if the train were still in motion or not fully halted. Stopping the train before this mode allows for a controlled and safe shift, reducing the risk of accidents or miscalculations in speed.

The other options do not adequately account for safety protocols. Gradually increasing speed while transitioning could lead to an uncontrolled situation. Receiving permission from the dispatcher is a necessary operational procedure in various contexts, but it does not specifically pertain to the required actions for transitioning to Release mode. Notifying passengers may be a good practice for overall communication but does not address the fundamental safety requirement of stopping the train first.