20‑115.1. Limitations on tandem trailers and semitrailers on certain North Carolina highways.
(a) Motor vehicle combinations consisting of a truck tractor and two trailing units may be operated in North Carolina only on highways of the interstate system (except those exempted by the United States Secretary of Transportation pursuant to 49 USC 2311(i)) and on those sections of the federal‑aid primary system designated by the United States Secretary of Transportation. No trailer or semitrailer operated in this combination shall exceed 28 feet in length; Provided, however, a 1982 or older year model trailer or semitrailer of up to 28 1/2 feet in length may operate in a combination permitted by this section for trailers or semitrailers which are 28 feet in length.
(b) Motor vehicle combinations consisting of a semitrailer of not more than 53 feet in length and a truck tractor may be operated on the interstate highways (except those exempted by the United States Secretary of Transportation pursuant to 49 U.S.C. 2311(i)) and federal‑aid primary system highways designated by the United States Secretary of Transportation provided that:
(1) Any semitrailer in excess of 48 feet in length shall not be permitted unless:
a. The distance between the kingpin of the trailer and the rearmost axle, or a point midway between the two rear axles, if the two rear axles are a tandem axle, does not exceed 41 feet; or
b. The semitrailer is used exclusively or primarily to transport vehicles in connection with motorsports competition events, and the distance between the kingpin of the trailer and the rearmost axle, or a point midway between the two rear axles, if the two rear axles are a tandem axle, does not exceed 46 feet; and
(2) Any semitrailer in excess of 48 feet is equipped with a rear underride guard of substantial construction consisting of a continuous lateral beam extending to within four inches of the lateral extremities of the semitrailer and located not more than 30 inches from the surface as measured with the vehicle empty and on a level surface.
(d) Notwithstanding the provisions of subsections (a) and (b) of this section which limit the length of trailers which may be used in motor vehicle combinations in this State on highways of the interstate system (except those exempted by the United States Secretary of Transportation pursuant to 49 USC 2311(i)) and on those sections of the federal‑aid primary system designated by the United States Secretary of Transportation, there is no limitation of the length of the truck tractor which may be used in motor vehicle combinations on these highways and therefore, in compliance with Section 411(b) of the Surface Transportation Act of 1982, there is no overall length limitation for motor vehicle combinations regulated by this section.
Whew! that was a mouthfull. I guess I need to read section 411, because after reading the last sentence, I'm confused.