What the Interstate System Was Built to Do
The word “Defense” in the system’s formal name—the National System of Interstate and Defense Highways—helps explain why the runway story sounds plausible. The 1956 highway program had a real military purpose: a connected network could move troops, equipment, and supplies across the country more reliably than a patchwork of local roads. It could also support evacuation and keep transportation moving if major routes were disrupted.
That purpose was about moving forces over roads, not turning ordinary highways into emergency airfields. Federal law did not require one straight mile for every five miles of interstate.
A Road and a Runway Solve Different Problems
A highway can look long and straight from above, but length alone does not make it suitable for landing an aircraft. A usable strip needs a clear, predictable approach and enough unobstructed pavement for the aircraft to touch down, slow, and exit. Interstate routes commonly have overpasses, signs, barriers, traffic, and changes in elevation; their lanes are also divided and interrupted by interchanges.
Those features make sense for controlling vehicle traffic and crossing terrain. They are serious obstacles for an aircraft approaching at speed. A stretch of road might happen to be usable in unusual circumstances, but that possibility is not the same as a design requirement for the national network.
The Military Logic Was in the Connections
The strategic value of the interstates lies in their reach: a vehicle convoy can travel between regions on a continuous, high-capacity system, rather than relying on disconnected roads. The network’s military role therefore fits the same engineering choices that serve civilian drivers—reliable links, controlled access, and routes capable of carrying heavy traffic. The “Defense” name refers to that transportation backbone, not a hidden reserve of improvised runways.
