Interesting history...

Here is an interesting history of automobiling trails and how the Interstate system came into being. It's a little bit wonk-ish, but would be very good if you needed to set a road trip in the early part of the 20th century.

And because I have politics on the brain, next time you get a conservative who thumps his chest and says that he's earned everything he's gotten in life with his own hands, ask him what he did to earn the Federal Interstate Highway system.