It seems to vary by city in the US. I've been places where it seems to do nothing. I've been places where it starts a signal change. I've been places where it

It seems to vary by city in the US. I've been places where it seems to do nothing. I've been places where it starts a signal change. I've been places where it enables accessibility features, as described in the article. And I've been places where it does absolutely nothing to alter the light's timing, but it does control whether the pedestrian light will turn white or not. The last of these is my least favorite, because it seems to engender the most confusion.