Not long ago, I was thinking about Route 66 (the TV series). It seemed like those guys drove that Corvette all across the country. If they did, they didn't do it all on Route 66. It runs from Chicago to Los Angeles, just 7 states, carefully bypassing Nevada, for some reason unknown to me. And route 50 is supposed to go from coast to coast (The Lincoln Highway), but it stops in Sacramento. California probably used the roadbed to build I-80 to the coast.
I guess its really hard to build a road across the country without stepping on individual states' toes.