That's the thing. I've looked into it, not super extensively honestly, but never found any project specification that included clauses or numbers about military use. Further, the infrastructure isn't overbuilt for the purpose, which is road transport of cargo. Trucks threaten to overburden the Interstate highways, which is why we have weight limits, and weigh stations to enforce them. Also, all.of the military vehicles I've seen on the highway are still just vehicles, modified from civilian models; even the tanks are not so.massive that they can't transport them on a typical flatbed trailer. The last thing that makes me doubt the military-use justification is that it's a double-edged sword: Our military can use them.to rapidly deploy forces, but invaders could also use them just as effectively, and to rapidly advance into the heart of our cities.

Eisenhower is called the father of the Interstate Highway, and he saw the need for economic reasons. The cost of construction was the primary fight, and "Defense" got added to the title of the bill authorizing it so they could justify spending some defense funds, but that looks awfully perfunctory, being added later.

You're missing the "privatized railways" and "trains need more grading" components.

Businesses need to ship cargo. However the private railroads road block attempts at public freight rail (which is massively more efficient) so the demand from businesses is to run truck traffic over highways which is where like 99.9% of road wear comes from.

Private railways also have no incentive to expand service (it costs a lot to properly grade for freight and they have regional monopolies. )