A bulletin order specifies that certain trains must be keyed 1-4-4-1. What does this signify?

The indication that the trains must be keyed 1-4-4-1 specifically relates to the operational configuration of the door controls. This keying pattern signifies that the train must be set up for two conductor operation, which is essential for safely managing passenger door operations, ensuring that both conductors are able to monitor and control access and egress at stations effectively.

Two conductor operation is particularly important in maintaining safety standards, especially in environments with high passenger volume or when operating in dual modes. Each conductor's ability to control the doors provides redundancy, which can be critical in various situations, such as emergencies or when coordinating with station personnel.

The other choices do not accurately reflect what the keying configuration entails. Speed limits, route changes, and maintenance logs are unrelated to the specific door operation protocols established by the keying pattern. Thus, the correct reasoning aligns with the necessity for coordinated control of train doors to promote safe operations.