The original 1956 plan for the Interstate system, however, gave the state only 769 miles of freeways[2]. A map of the state's original allotment, taken from the 1966 edition of NCR&TB, illustrates this below. Most noteworthy is that I-77 was planned to end in Charlotte, and I-40 was planned to end in Greensboro.

Around 1966, Federal approval was granted to extend I-77 into South Carolina and I-40 to Raleigh. Most of the original 1956 Interstates, including the I-77 extension into South Carolina, were completed by the mid-1970s. The most arduous stretch of road to build was I-40 through the Smokies, completed in 1967 through territory nobody had attempted to build a paved road through before. North Carolina didn't have any signed 3-digit Interstates until the early 1980s, but parts of what would become I-240, I-277 and I-440 were built by 1970. 

Starting in the late 1980s, a second boom of Interstates occurred. Between 1987 and 1991 I-40 was finished to Raleigh and then to Wilmington, I-277 was finished, I-440 was signed and I-485 construction began. More recently, part of I-540 has opened north of Raleigh. Newcomers I-73 and I-74 were first signed in 1997, and have gradually been posted over more and more miles of freeway since then. 

In the future the state will complete four urban beltways, as well as extend I-26 northward into Tennessee. 

For more information, check out the NCRoads.com State Map or the individual Interstate pages.