I can't edit my previous post, but that should read SOUTHbound traffic headed into Pittsburgh.
This article quotes a man who remembered an odor of decomposition a few months ago:
http://triblive.com/news/adminpage/5243734-74/remains-allegheny-county#axzz2nM92f3mW
And it states the UID might be a male based on clothing, which is described as a t-shirt, shorts and tennis shoes.
Those are some very vintage items and they immediately bring to mind the Red White & Blue Thrift Store, which is 0.6 miles from the site where the UID was found. They carry items like this that appeal to the hipster/retro crowd.
The store uses a distinct price tag, with the price and date the item was put on the shelf written in permanent marker. If the items have these stickers, the dates on them would indicate when they were purchased and ended up in the woods with the UID.