UPDATE! March 2017 This map has been updated again to allow easy editing. Corrections and additions were made. Colors were changed to match standard Google Map colors.
UPDATE! Jan 2017 I have made the main map default to terrain so you can see how the early routes followed the land. You can click on Map and change to regular view or over to satellite view to see what the ground looks like. Maps are now managed through Google Maps API which gives a lot more flexibility. Click on link above for full page version.
Color codes for the roads;
Red = oldest alignments. 20's - 30's
Brown = 30's - 40's
Green = 40's - 50's
These dates are approximate because Route 66 was continually being moved, re-routed, improved and changed. But it will help you understand in which order the alignments were made.
This map shows most of the alignments that Route 66 followed. The last alignments were Interstates and are not drawn on the map. The lines were originally drawn using DeLorme Topo maps and then converted over to .KML format. Other software I have found very useful is RidewithGPS, GPSBabel, and GPSVisualizer.