Titles of roads and why??

From:  "Steve"

Why do we drive on parkways and park on driveways? Further, why are they still called overpasses when you drive over them? Shouldn't they then be called underpasses?

Paul gave us his best attempt at answering the question: 

I cannot speak as to why we drive on parkways and park in driveways, but there is a difference between an overpass and an underpass. It all has to do with which road remains level and which one does not.
An overpass arches up and over a level road. An underpass dips and passes under a level road.