Section 19A. Any provisions of sections thirty and thirty A of chapter eighty-five to the contrary, notwithstanding a motor vehicle having two axles, which vehicle with its load weighs not more than forty-six thousand pounds, and a motor vehicle, trailer, semitrailer, semitrailer unit or tandem unit having three or more axles, which unit or vehicle with its load weighs not more than eighty thousand pounds, may travel on a public way without a permit as required by sections thirty and thirty A of chapter eighty-five; provided, however, that no such motor vehicle, trailer, semitrailer, semitrailer unit or tandem unit, the weight on any axle of which, measured at the ground, exceeds twenty-two thousand four hundred pounds, or, in the case of axles spaced less than six feet apart, eighteen thousand pounds, shall so travel without such a permit; and provided, further, that such motor vehicle, trailer, semitrailer, semitrailer unit or tandem unit may not travel on a public way without such a permit if the overall gross weight on a group of two or more consecutive axles thereof exceeds the gross weight produced by application of the following formula:

W = 500 (LN/N–1 + 12N + 36)

Every operator of a motor vehicle operated on a way shall, upon request or direction of any officer authorized to enforce the provisions of this chapter, operate such motor vehicle with any trailer which may be attached thereto to and upon the nearest scales available to the commonwealth within a distance of not more than five miles and permit the weighing thereof together with its load. Whoever refuses to comply with the request or direction of such officer shall be punished by a fine of not less than three hundred nor more than five hundred dollars and the registrar may suspend such operator's license for not more than ninety days. Whenever such vehicle has been so weighed and is found to weigh in excess of the limits provided by this chapter, no person shall further operate it upon a way unless the gross weight shall have been reduced to comply with said limits by removal of the excess weight.

Notwithstanding any general or special law to the contrary, the maximum gross vehicle weight limit, bridge formula limit and axle weight limit for any vehicle or combination of vehicles equipped with an idle reduction system may be increased by a quantity necessary to compensate for the additional weight of the idle reduction system as provided for in 23 U.S.C. section 127. The additional weight increase allowed under this paragraph shall not be greater than 400 pounds. Upon request by an appropriate law enforcement officer, the vehicle operator shall provide proof that the idle reduction technology is fully functional at all times and that the gross weight increase is not used for any purpose other than for the use of an idle reduction system. For purposes of this section, an idle reduction system shall be any system that provides heating, cooling or electrical service to a commercial vehicle cab to reduce vehicle idling.

No motor vehicle, trailer, semitrailer, semitrailer unit or tandem unit shall be operated, nor shall the owner or bailee thereof require or authorize such operation, when the gross weight of such motor vehicle, trailer, semitrailer, semitrailer unit or tandem unit exceeds the weight provided by this chapter or that specified in any permit issued by the commissioner of highways under sections thirty and thirty A of chapter eighty-five, whichever is greater, but in no event in excess of the gross weight for which such vehicle is registered, except in the case of a vehicle owned or leased by a carrier that is not domiciled in this commonwealth and which has a permit under section thirty A of chapter eighty-five to operate in excess of its registered gross weight; nor shall any person load or cause to be loaded such vehicle in excess of such weights. If the gross weight of any such motor vehicle, trailer, semitrailer, semitrailer unit or tandem unit does not exceed one hundred and five per cent of the maximum gross weight provided by such permit, such motor vehicle, trailer, semitrailer, semitrailer unit or tandem unit shall not be deemed to be operating in violation of the provisions of sections thirty and thirty A of chapter eighty-five; but if the gross vehicle weight of such motor vehicle, trailer, semitrailer, semitrailer unit or tandem unit does exceed the said one hundred and five per cent of the maximum gross weight provided by said permit, any penalty provided by this chapter shall be determined on the difference between the actual gross weight of such motor vehicle, trailer, semitrailer, semitrailer unit or tandem unit and the weight authorized by this section or the weight authorized by the said permit for such motor vehicle, trailer, semitrailer, semitrailer unit or tandem unit, whichever weight is greater, at the time of such violation.

Upon the finding by an officer authorized to enforce the provisions of this chapter that a motor vehicle, trailer, semitrailer or semitrailer unit exceeds the said one hundred and five per cent of the maximum gross weight provided in said permit, or otherwise violates the conditions of any permit issued under sections thirty and thirty A of chapter eighty-five or section nineteen of this chapter, said officer may exercise reasonable discretion to prevent the continued transport of a load that is the principle cause of the violation. Neither the finding of such violation, nor the exercise of such reasonable discretion, however, shall be construed as nullifying or revoking any such permit, or as having any effect, beyond the actual citation of the violation, on the assessment of any penalties provided under section twenty.

In the weighing of any motor vehicle or trailer or semitrailer or semitrailer unit or tandem unit under this chapter, portable scales may be used; provided, however, that such scales have been approved by the director of standards under section twenty-nine of chapter ninety-eight; and, provided further, that such scales shall be inspected at least once in each year by the director of standards or his inspectors. No officer authorized to enforce the provisions of this chapter shall detain for weighing on portable scales more than two motor vehicles, with or without trailers or semitrailers attached thereto, at any one place at any one time.

In any prosecution for a violation of this section or of section nineteen or section thirty of chapter eighty-five, a signed certificate on oath of any person appointed under section eighty-seven A of chapter forty-one of the weight of any motor vehicle or trailer or semitrailer shall be admissible in evidence without further proof, and shall constitute prima facie evidence of the weight of the motor vehicle or trailer or semitrailer or semitrailer unit or tandem unit described in such certificate. The said certificate shall be in such form as the registrar shall prescribe and shall be signed and sworn to by a person appointed under said section eighty-seven A and present at the weighing of such motor vehicle or trailer or semitrailer or semitrailer unit or tandem unit, and the court shall take judicial notice of the signature of such person and that he is so appointed.

In any claim for bodily injuries or for damage to property arising out of such direction to a scale location or such weighing, any officer or employee of the commonwealth authorized to enforce the provisions of this chapter may file a written request with the attorney general that the attorney general defend him against an action for damages for bodily injuries, including death, or for damage to property arising out of such officer's enforcement of this section, and the provisions of section three B of chapter twelve shall apply to such action as if it had arisen out of the operation of a motor vehicle.

Notwithstanding the foregoing provisions of this section, nor any contrary provisions of section thirty of chapter eighty-five, a construction type motor vehicle or a motor vehicle designed and used for the hauling of refuse having two axles, which vehicle with its load weighs not more than twenty-three tons, or a motor vehicle carrying bulk feed, or a construction type semitrailer unit or tandem unit or motor vehicle having three axles, or a semitrailer unit or a tandem unit or motor vehicle having three axles while carrying liquid petroleum products, or a motor vehicle having three axles and designed and used for the hauling of refuse, which vehicle with its load weighs not more than thirty tons, may travel on a way while engaged in hauling construction materials or liquid petroleum products or bulk feed or refuse without a permit as required by said section thirty of said chapter eighty-five; provided, however, that the gross weight of such vehicle as operated does not exceed the gross vehicle weight rating as established by the original manufacturer of the chassis; provided further, that such a vehicle operating under a general registration and general registration number plate issued to a farmer pursuant to section 5 may carry up to its gross vehicle weight rating; and, provided further, that the vehicle is duly registered in this commonwealth for such weight. The operator of such a vehicle shall at all times comply with the speed limitations as provided by section seventeen.