(a) Motor trucks shall be equipped with rubber tires.

(b) Not more than one trailer shall be attached to one motor truck. However, two vehicles may be towed in driveaway-towaway operations, including double saddlemount, if the operations conform with the safety regulations of the Federal Motor Carrier Safety Administration relative to coupling devices and towing methods as set forth in 49 C.F.R. §§ 393.70 and 393.71 of those regulations as they may from time to time be amended. As used herein, driveaway-towaway operation means any operation in which any motor vehicle or motor vehicles, new or used, constitute the commodity being transported, when one set or more of wheels of any such motor vehicle or motor vehicles are off the roadway during the course of transportation, whether or not any such motor vehicle furnishes the motive power.

(c) Notwithstanding subsection (b) of this section, on the National System of Interstate and Defense Highways and those classes of qualifying Federal-aid Primary System highways as designated by the Secretary of the U.S. Department of Transportation, commercial motor vehicle combinations consisting of a truck tractor and two trailing units may be operated with the approval of the Vermont Secretary of Transportation. (Amended 1963, No. 62, § 1, eff. April 30, 1963; 1983, No. 74, § 1, eff. April 28, 1983; 1983, No. 102 (Adj. Sess.), § 3.)