Answer:
When it comes to me you go on red and stop on green.
You heard me before and then again. Afterward I die, until you call me again. What am I?
The more you have me the less you see. Shine a light on me and I shall flee.
Crooked as a rainbow and slick as a plate ten thousand horses can't pull me straight.
A dragon's tooth in a mortal's hand, I kill, I maim, I divide the land.
When I'm born I fly. When I'm alive I lay. When I'm dead I run.