What action must the train engineer take when acknowledging a transition in mode on the system?

When acknowledging a transition in mode on the system, the action that the train engineer must take is to touch the appropriate signal on the screen. This step is essential because it directly confirms the engineer's awareness and acknowledgment of the change in operation mode. By interacting with the system interface, the engineer provides an active response, which is necessary for ensuring that the system is operating correctly and safely in the new mode.

The choice to touch the appropriate signal on the screen is designed to enhance operational efficiency and accuracy. This interactive approach allows for real-time updates and immediate feedback, which is crucial in a rail environment where quick reactions may be necessary to maintain safety and performance standards.