Very cryptic. I think we could interpret this as an extended metaphor based around the theme of personification. I would rule out any zoomorphism because of the "two wheels" line. The "wheels" shake this whole thing up and make it more difficult. However, as I said, it could be a metaphor. If they're not literal wheels, then what are they? Possibly just a means of getting around. Transport.
When discussing the "I am non-existent" line, I would look much deeper into it than the subject being physically, not there. Perhaps it is a person or animal's sense of un-importance. Or perhaps an object that nobody takes notice of.
"I gratify another commodity" is also interesting. Gratifying is pleasing something, indulging it in something. And a commodity is a useful or valuable thing, of which we have two of.
At a guess, this riddle is personifying the Bus Stop.
In relation to the "two eyes", I really don't know how a bus-stop has two eyes. Perhaps the bus stop is fitted with security cameras, something like that. The "two wheels" line, to me, connotes the Bus/Buses. There could possibly be two buses that circle TranZit so we don't have to wait ages for one to turn up. The Bus stop is talking about its two lives, one where we are in it, and another where we are elsewhere. In one, it is non-existent. Nothing happens. It just stands there and nobody takes any notice of it. However, when we are at the Bus Stop fighting off Zombies, it helps us out as best it can. It "gratifies another commodity". It acts as a place for the bus top possibly re-fuel or for us to fix it up and add parts to it. I link the bus to being the commodity, because it fits in with my idea of there possibly being two buses.
That's just my rambling brain spewing things out. The more I read through what I just typed the more I find holes in it. I don't think there are two buses in TranZit. I'm pretty sure there's only one. But hey! There's probably something useful in all my nonsensical babble