[via io9.com]
It would have followed Pennsylvania Avenue right past a residence at no. 1600. (It's public housing, though :-/)
There's a small amount of info (and two small scans) at http://longstreet.typepad.com/thesciencebookstore/2011/01/superbad-ideas-superhighway-through-the-center-of-washington-dc.html
I got a chuckle out of that self described historian with no sense of history. Just because it's a bad idea now doesn't mean it wouldn't have been a bad idea then.
Oh, it would always have been a bad idea.
Anyway, revenge for Atlanta?