I see almost every freeway I go on, I see street art. (Sorry ahem, I meant graffiti, and I don't know why they're doing that).

My personal aspect of street art is amazing. I mean, you're seeing at least a couple hundred graffiti artists drawing graffiti everywhere. The most graffiti I've seen in one place would be in San Francisco CA. So, the question I'm asking is, Why are people writing and drawing stuff on freeway walls? Why do they do that? Is that how they show their inital feelings inside?