The Narragansett Bay Wheelmen have a few maps in the club library. From the Mt Hope Bridge to Newport, try this map, the bridge isn't as bad as the very first section of ropad you face when you come off of the bridge where there are four lanes and no shoulder, ditto for the section of 138. Could go the route in reverse to avoid some of it is but it is longer.
http://www.nbwclub.org/maps/nbw064-newportcircuit.pdf
Here is another NBW ride from Providence to Boston, it is south to north and it is obviously old. Might give you an idea.
http://www.nbwclub.org/maps/nbw132-p...nce-boston.pdf