Answer:
A dragon's tooth in a mortal's hand, I kill, I maim, I divide the land.
When it comes to me, you go on red and stop on green. What am I?
My first half means container. Not a lot of people understand my language.
Four fingers and a thumb, yet flesh and blood I have none. What am I?
Goes over all the hills and hollows, Bites hard, but never swallows.
Almost everyone needs it, asks for it, gives it. But almost nobody takes it.