N.C. Gen. Stat. § 136-89.187

The Authority Board is prohibited from converting any segment of the nontolled State Highway System to a toll facility, except for a segment of N.C. 540 under construction as of July 1, 2006, located in Wake County and extending from the N.C. 54 exit on N.C. 540 to the N.C. 55 exit on N.C. 540. No segment may be converted to a toll route pursuant to this section unless first approved by the Metropolitan Planning Organization (MPO) or Rural Planning Organization (RPO) of the area in which that segment is located.