ComingSoon.net has an excellent interview with "Cars" director John Lasseter. Check it out.
UPDATE: Here's another interview, this time with The Australian. It includes this excerpt about Route 66.
Observation is important, says Lasseter, who refers to the small town on America's Route 66 that is integral to the story. Bypassed by the major highway, it represents old-fashioned values.
"They say a picture is worth a thousand words. When you come to some of these towns, you can tell they were really vibrant but now the customers are all gone. You can tell from the peeling paint, the cracks in the asphalt, the dust, the sun-bleached nature of everything. All that stuff is extremely difficult to do with a computer."