What control method ensures that an elevator system does not change direction until the highest call is answered?

The selective collective control system is designed to efficiently manage elevator traffic by prioritizing calls in a way that ensures an elevator will first respond to all calls in one direction before switching its direction. In this method, when a passenger calls for an elevator, the system collects calls and responds to them based on the direction of travel; it will not change direction until all calls in that particular direction have been fulfilled. This approach minimizes waiting times and improves efficiency, as it helps prevent unnecessary stops or directional changes, especially in buildings with multiple floors and high traffic.

In contrast, single automatic control typically suggests a more straightforward response to requests without consideration for optimizing directionality, which might lead to inefficiencies in high-traffic scenarios. Two-way switch control usually allows for manual operation, which does not inherently prioritize calls based on direction. Sequential control might indicate a predetermined order of operation but lacks the flexibility of responding to real-time requests in a prioritized manner as selective collective control does.

Therefore, selective collective control is the most suitable method for ensuring that an elevator only changes direction after addressing the highest call in a specific direction, thereby enhancing overall system efficiency.