The interstates were originally justified as for Defense because Eisenhower had long noted that it was very time-consuming to move military supplies across the country. The I’states vastly improved that situation as well as made it easier to go visit Grandma.
Yeah, I understand the “justification” on the Interstate Highway system. It’s up there with all the other uses of the Interstate Commerce Clause for expansions of Federal power.
But I still like the result!