Someone mentioned seeing this quite a while ago, so when we went through there this week I kept an eye out for it. Sorry for the 'Oh crap there it is grab the cell phone quick!' quality of the picture, but
that? That right there? Is a green dump truck.
There's even a Decepticon logo on the side of the cab, though you can't see it at all in the picture.
If anyone is ever in the area and wants to try getting a better picture, it's on I-5 in Oregon, between Salem and Albany, just past Enchanted Forest if you're heading south.