As I sit at home and look out at Route 30 - the Lincoln Highway - I sympathize with Eisenhower's misery in using it to cross the nation in 1919. And I realize that a national highway system for defense was in the nation's mind for sometime...but what specific threats were Eisenhower taking into account when he started work on the system again? It doesn't seem to be designed with Russia in mind.
A national network of superhighways had been proposed during the Roosevelt and Truman Administrations, so I have real qualms about primarily crediting Ike's 1919 convoy, his observations in Germany, or attributing the program to defense. As Earl Swift notes in The Big Roads, p. 157: "When Dwight Eisenhower took office in January 1953, the Interstate Highway System had officially existed for more than eight years....He entered the Oval Office professing an interest in building 'a network of modern roads'.... He didn't know that the executive and legislative branches had already worked out the details of the network he sought." All that remained was figuring out how to pay for it, and the Eisenhower Administration played virtually no rôle in that congressional saga.
Throughout the years of congressional debate, military strategists repeatedly testified that they didn't need any particular routes or geometric specifications, always saying that highways built to promote commerce would also serve their needs. I am not aware of any serious civil defense or military rationale that was part of congressional debate. The words "and Defense" were added to the name of the "National System of Interstate Highways" in conference committee, almost as an afterthought, and played no role in congressional voting. See Congressional Record 102, Part 8, pp. 10991-10997. The definitive source on this history is Rose, Mark H. Interstate: Express Highway Politics, 1939-1989.
Remember that Interstates were not the first American superhighways. There were short forerunners built in the 1920s, limited-access parkways near New York and Washington built as Depression public works programs, the prewar urban superhighways of Detroit and Chicago and Southern California, the Pennsylvania Turnpike, and the postwar turnpike craze it set off from the Eastern Seaboard to the industrial Midwest. The breakthrough in 1956 was getting a funding agreement through Congress, a battle in which the Eisenhower White House—still dithering about all-toll financing—was largely irrelevant.