Only post roads. And the language says “establish”, not fund and maintain.
2. The idea of constructing a road that would be used exclusively for the delivery of mail without access by any other user was unheard of -- even in the 1790s.
3. I don't have a problem with privately-owned roads, but there are major flaws in that whole concept and there's a good reason why many of the toll roads that have been sold off to private investors in the last decade have turned into financial disasters.