Answer:
When it comes to me you go on red and stop on green.
I am a portal to another world which you cannot enter. Only you can see me but I can't see you.
What has one eye but cannot see?
I don't live within a house, nor do I live without. Most will use me when they come in, and again when they go out. What am I?
I run through hills. I veer around mountains. I leap over rivers. And crawl through the forests. Step out your door to find me.
Whoever made me don't want me. Whoever bought me don't need me. Whoever use me don't know me.