In 1956, Congress authorized the National System of Interstate and Defense Highways (I didn't know they were also called Defense Highways). Using tax revenues from gasoline, tires and other sources, it was to provide a nationwide system of 41,000 miles of interconnected "super highways" or "Super Slabs" as the Route 66 folk like to call them.
Each state was to receive 90% in federal aid with the government in D.C. determining which ones to build. North Carolina was slated for 769 miles: I-85 running 233 miles from Virginia to South Carolina; I-40 219 miles from Greensboro to Canton; I-95 , 182 miles from Weldon to Lumberton; I-77, 96 miles from Virginia to Charlotte; and I-26, 40 miles from Asheville to South Carolina.
I-40 has since been extended from Canton to the Tennessee border going west and to Wilmington on the east. Its 22-mile stretch near Asheville through Pigeon River Gorge was particularly difficult to build.
For the most part, the interstates replaced the federal highways. However, lengthy sections of US Highways 1, 29, 64, 70, 74 and 421 have been rebult as limited-access, interstate-style roads.
Those Super Slabs. --RoadDog