Someone who is an aide in a high school history classroom told me she heard this from a teacher in class. It sounds plausible but I wonder if it's true.
I’ve never seen any evidence of such a rationale in the documents of the time.
US railroads were private companies, and that was accepted as the way things would remain.
Meanwhile, truck traffic had become very important since the 1930s for the door-to-door convenience it offered, and had played a huge role in the industrial economy during the war. The nation’s first intercity superhighway, the Pennsylvania Turnpike, had opened in 1940 to immediate success, and many states were anxious to build similar facilities, and began work on toll roads and other improvements as soon as they could.
Eisenhower’s role in all this is quite minor. 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."
From my understanding, Eisenhower became a huge proponent for the interstate highway system after seeing how quickly armor, troops, and supplies could be moved on european highways during WW2 (most notably Germany's). It's a lot easier to move divisions on paved roads, instead of having to slog through muddy roads.