Boston Traffic Signals: A Bestiary

So, we're all hopefully familiar with red, yellow, and green. Even blinking red and blinking yellow should be more or less comprehensible. But this is Boston. I've seen others. I've seen blinking green, and I think it's useless the way we use it. I've seen (red & yellow). I've seen blinking (red & yellow). They also seem to be slightly less useful than nothing.

Today I saw (solid red & blinking yellow). I'm pretty sure that this means "Here in Boston, we don't want just anybody surviving."