Final answer:
The three amber lights above a platform indicate that the train is approaching, which alerts passengers to be ready for boarding.
Step-by-step explanation:
When the three amber lights located above the platform for a particular track at a gap station are lighted, it means that the train is approaching. These lights serve as a visual cue to passengers that a train is imminent, and they should prepare to board.
The movement of the crowd at a station often indicates the regularity of a train's schedule, and experienced commuters may sense changes without needing to check the schedule board. However, the amber lights provide a definitive signal of a train's arrival for all travelers.