(a) As used in this article, the term:

(1) "Bimodal semitrailer" means a detachable load-carrying unit designed to be attached to a coupling on the rear of a truck tractor by which it is partly supported during movement over the highway and designed either with retractable flanged wheels or to attach to a detachable flanged wheel assembly for movement on the rails.

(2) "Combination of vehicles" means a semitrailer pulled by a truck tractor or a semitrailer and trailer pulled by a truck tractor operating in a truck tractor-semitrailer-trailer combination.

(3) "Extendable semitrailer" means a semitrailer that has been manufactured for the purpose of extending the frame to increase the overall length for the purpose of transporting single-piece loads.

(4) "Semitrailer" means a detachable load-carrying unit designed to be attached to a coupling on the rear of a truck tractor by which it is partly supported.

(5) "STAA system" means the National Network and the Access Routes to the National Network as allowed under the federal Surface Transportation Assistance Act (STAA), as amended.

(6) "Trailer" means a detachable load-carrying unit designed to be attached to a coupling at the rear of a semitrailer and capable of support in operation without the truck tractor.

(7) "Truck tractor" means the noncargo-carrying power unit that operates in combination with a semitrailer or trailer, except that a truck tractor and semitrailer engaged in the transportation of automobiles may transport motor vehicles on part of the power unit.

(b) Unless exempted in Code Section 32-6-25 or so authorized by a permit issued pursuant to Code Section 32-6-28, the following length limits shall apply:

(1) Trailer and semitrailer lengths:

(A) Truck tractor-semitrailer-trailer combinations shall have trailers and semitrailers that do not exceed 28 feet in length;

(B) Truck tractor-semitrailer combinations shall have semitrailers that do not exceed 53 feet in length, unless signs are posted that indicate semitrailer length restrictions;

(C) On interstate and STAA system routes, single-piece loads may be transported on an extendable semitrailer that exceeds 53 feet, provided that no pieces will be loaded end to end and the semitrailer does not exceed 75 feet in length; on roads other than the interstate and STAA system routes, the foregoing provisions of this subparagraph shall also apply, except that the overall length shall not exceed 100 feet. Empty extendable semitrailers or extendable semitrailers transporting a single-piece load of 53 feet or less shall be required to maintain a semitrailer length of 53 feet or less. When the semitrailer is extended as described in this subparagraph, the rear extremity of each extendable semitrailer or load shall be marked with a four-inch multidirectional amber strobe light and with 12 inch bright red or orange warning flags on the rearmost of the load or semitrailer;

(D) Maxi-cube combinations shall have a cargo box that does not exceed 34 feet, provided that the pair of cargo boxes together does not exceed 60 feet and the overall length, including the power unit, does not exceed 65 feet; and

(E) Trailer and semitrailer length requirements in this paragraph shall not apply to automobile and boat transporters; however, no unit of the vehicle shall exceed 56 feet in length; and

(2) Overall truck tractor-semitrailer or truck tractor-semitrailer-trailer lengths:

(A) Maxi-cube combinations shall have an overall length that does not exceed 65 feet;

(B) Saddlemount and saddlemount with fullmount combinations shall have an overall length that does not exceed 75 feet; and

(C) All other combinations of truck tractor-semitrailer or truck tractor-semitrailer-trailer operated on roads other than interstate or the STAA system of roads shall have an overall length that does not exceed 100 feet, unless signs are posted that indicate length restrictions. This maximum length shall include the federal allowance for automobile and boat transporter loads to overhang up to three feet over the front of the vehicle and overhang up to four feet over the rear of the vehicle.