They were supervised by a station manager that would handle the security requirements for each departing train.
The train handling became optimized to allow for less than a minute from arrival to departure at a stop which triggered the usage of loudspeakers and platform displays.
[2] The electric relay interlocking boxes were later replaced by electronic control boards where the train indication is just a text element on the video display.
In a centralized electronic interlocking the current train location and identification is used to predict the arrival at the next stop allowing for countdown clocks for passenger information.
The term passenger information display has widely replaced the term platform display as station design can include different types of information displays - like a departure board in the main hall, a shorter list in the tunnels and an announcement of the next train on each platform side - which all get their information from a central electronic railway control system.