the green one depeltes just like the red one does. there'd be no way to tell the difference between them, other than by the color.
no reason to change what they are right now. if you really need to know when it's almost your time to go, wait for the flashing hand to warn pedestrians the light is about to change
plus, if we were to give people a countdown, people would just start timing shit for cutting people off and trying to hit the light just as it changes without slowing down, that kind of thing
I LIKE MY LIGHTS THE WAY THERE ARE OKKKK?!?