What role does the conductor have when three green lightbulbs illuminate?

The conductor plays a vital role in the safety and efficiency of train operations. When three green lightbulbs illuminate, this indicates the signal to proceed. In this context, the conductor's responsibility is to ensure that the train is ready for departure. This includes checking that all doors are properly closed and secured to ensure passenger safety before signaling the operator.

By managing the closing of doors and communicating readiness to the operator, the conductor ensures that no passengers are at risk of injury and that the departure can happen smoothly and on time. This specific action is critical as it directly relates to maintaining safety standards and operational procedures.

While other roles, such as checking passenger count or ensuring the train is on schedule, are important in the overall operation, they do not correspond directly to the immediate actions required once the three green lights illuminate. The focus here is on the safety procedure related to train departure, highlighting the conductor's role in facilitating a safe and efficient launch of the train service.