In the fifties when the plans for the National Interstate Highway was being planned, the engineering standards were much different than the ones used in new construction today.
An example is in 1933 the Field Act was passed in California, it set the earthquake construction standards for public schools. Today we can't build a pump house in the farm lands using those standards. In the fifties the 4"x4" diesel engings couldn't haul 80,000 pound payloads. Today's semi's can haul a lot more than that.
Old standards for trucks hauling lighter loads and lower speed limits are in a large part responsible for rapid deterioration of our highways today.
I you want to hear my opinion about why California's highways and freeways and state highways and public streets are irreparable, PM me and we can talk about the time A Giant Turkey stopped all highway maintenance in CA.
Furthermore, when a State petitions for Federal monies for repair of streets and highways, the Feds do not fund "IMPROVEMENTS", a state has to put back what was there, they are not allowed to use federal funds for improvements unless, they receive an improvement "GRANT". Never heard about one of those did you.