Post Apocalyptic Rpg Resource - U.S. Routes as a Subway Map

Imagine your PC's are exploring an alternative prime material plane were there are no highways at all. Here the ultimate in megadungeons has been put into practice with an incredible underground highway system of incredible complexity. The underground fiends  of the Fiend Folio, Monster Manual, etc could all fit down here & still have room for more. 

From the original artist "my series of transit map-style diagrams - this time, of the U.S. Highway system. That's U.S. Routes (like Route 66), not to be confused with the newer Interstate Highway system (I-5, I20, etc.). Without a doubt, this is the most complex map of this type I have attempted."  Take an exalt Cameron Booth

 You can view the image Here