What do three illuminated green lightbulbs at a terminal indicate to the conductor?

The indication of three illuminated green lightbulbs at a terminal is a clear signal to the conductor that the train's doors should be closed and that it is time to notify the train operator to proceed. This signaling system is essential for maintaining safe and efficient train operations, ensuring that all passengers have entered or exited the train before it departs.

When the lightbulbs are illuminated in this manner, it suggests that the train is ready to move and that the conductor is responsible for checking that all safety protocols related to closing the doors have been followed. The conductor must ensure that there are no remaining passengers on board once the doors are closed, as safety is paramount before proceeding to the next segment of the journey.

The other options focus on different aspects of train operation. Preparing for the next train arrival typically involves different signals and notifications that are designed to manage the timing and scheduling of upcoming services. Checking for remaining passengers would usually occur before doors are closed, not after, as indicated by the lights. Adjusting speed for the next segment is also a separate procedure governed by other signals that ensure the train operates within safe speed limits and adheres to the track conditions ahead.