From what I remember when I was a regular NYC subway rider and what I see on current videos, there usually are signals mid-platform at some/all stations which are amber (or red). I am curious as to why these signals are in use. The operator knows that the end of the platform approaches, and the signal beyond the end of the platform usually is green or amber. What is the purpose of these signals
Station timers are mainly to make sure the train operator approaches and enters the station at an appropriate speed.
In the case of Canal St on the A,C,E for example- there are switches at the end of the platform and of there is a train crossing over it is to protect that train. Even if the signals at the end of the platform are clear, the mid platform signals are still active.
Another example is if the station is on a downward grade, it is to make sure the train stops properly.
There are other reasons which others will post (the ones above are the only ones I can think of at the moment).