Does anyone have anything official from the Dixie Highway Association that details which routes were considered part of it, and which were mainlines or spurs? http://www.us-highways.com/tzimm/dhmap23.htm is too early to have all the connections in Florida, and doesn't clearly show which were the main routes.
Lacking response, I'll post what I've found:
November 1923 http://books.google.com/books?id=itA8NkoBsZkC&pg=PA9
Eastern Branch ("only official routing" - meaning what?): SSM to Miami
*Bay City to Detroit via Port Huron
*Cincinnati to Lexington via Cynthiana
Western Branch: SSM to Marco
*Grand Haven to Niles via South Haven
Chicago to Dayton
and other branches on the map but not listed:
*Knoxville to Chattanooga
*Chattanooga to Cartersville via Dalton
*Atlanta to Waynesboro
*Macon to Jacksonville
*Marco to Miami