The upper portion is a indicator to the engineer that the wayside system is working. It has a microphone that is activated by the wayside horn. If no indication is observed, the engineer must then use the trains horn upon approach.

There are often 4-6 “speakers” per crossing that are focused on the intersection. They are set to produce the required decibel level in the crossing. To produce that same decibel level from the train horn means it most be much louder at the locomotive to meet that same standard in the crossing, this is how/why it less disturbing to the community around such crossing.