I think you are talking about what is termed "Approach Lighting" for signals. Wouldn't it be easier to just light up your signals when the block becomes occupied. I get that you are only turning on the signal for the direction of travel. That one function shouldn't be too hard for an Arduino.
Block signals are a funny thing. Because they occur where one block starts and another block ends, you can think of them as both an entry signal and an exit signal. I tend to think of them in terms of entry signals because it's the next block and those that are further ahead that the signal represents. The important thing about approach lighting is that the signal be lit before the train arrives.
Good work!
