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 drawn using DeLorme Topo maps and then converted over to .KML format. So some of the lines may not be exactly on the road due to the differences in the two data sets of the maps. They should be "close enough" to figure out what road was intended.
The DeLorme map system has some of the best drawing functions I have found. That makes it very powerful for documenting roads, locations, and points of interest. The drawing is done in "layers" so you can draw over one layer without disturbing it and also turn layers on and off at will. Their Topo North America is about the least expensive Topo map available. Perfect for exploring some of the oldest non-paved sections in Arizona and California. The system I use allows me to draw/edit, convert and then upload very quickly so editing is not difficult at all. Other software I have found very useful is GPSBabel, GPSVisualizer and the Google Earth embed gadget.
By publishing this in Google Maps you get all the powerful features they have without having to write a bunch of code. I really like the ability to zoom in close or back off to see more. The satellite view and terrain view are great for understanding how the early alignments followed the terrain they crossed.
The one thing I am still working on is a limitation of .kml and Google Maps. My DeLorme maps on my laptop include line styles. There are dashed and dotted lines showing non-paved and non-drivable sections. Right now I have not found a good way to translate this because Google does not support line styles. I am trying to find a way to display this information in Google Maps without a complete manual edit of all the lines.