Train operators' announcements should be transmitted via local radio to the approaching station, allowing the operator to prepare customers on the platform to board. The exterior train speakers are insufficient for this purpose.
Here are some examples of actual announcements I've heard for which the system could be of use. And the proposed system could be implemented as part of other requested audio improvements.
"customers please step back from the platform"
" please walk forward 6 car short train"
"train right behind us"
"train approaching is out of service"
"this train will be express ..."