N.H. Rev. Stat. § 266:18 — NH Code / Title XXI / Chapter 266 / Section 18
266:18 Weight on Interstate and Defense Highway System.
Status: in_force

The driving on the interstate and defense highway system of this state of any vehicle or combination of vehicles exceeding the limitations of this section is hereby prohibited. I. Maximum tire and axle gross weights allowable: (a) The manufacturer's load rating for the tires. (b) When being driven with a gross weight in excess of 73,280 pounds: (1) 20,000 pounds per axle on axles more than 8 feet apart; (2) 17,000 pounds per axle on axles not more than 8 feet apart; (c) When being driven with a gross weight not in excess of 73,280 pounds: (1) 22,400 pounds per axle on 3-axle single unit vehicles and on all other vehicles with axles 10 feet or more apart, including combination vehicles; (2) 18,000 pounds per axle on axles of vehicles less than 10 feet apart, except 3-axle single unit vehicles. (d) Two axles less than 40 inches apart shall be considered as a single axle unit. II. Maximum allowable vehicle gross weights: (a) For 2-axle vehicles, 33,400 pounds. (b) For single unit 3-axle vehicles, 47,500 pounds, or a gross weight not in excess of that produced by application of the weight formula as defined in subparagraph (h), whichever is greater, as shown in table III. (c) For single unit 4-axle vehicles, provided that such vehicles shall have drive on 2 rear axles, and the tridem may contain not more than one retractable axle and, if not factory installed and load equalizing, must provide a system of load equalization by hydraulic, pneumatic, or mechanical means, and be equipped with brakes: (1) 47,500 pounds, or a gross weight not in excess of that produced by application of the weight formula as defined in subparagraph (h), whichever is the greater; or (2) If a heavy duty recovery vehicle, 75,000 pounds, or a gross weight not in excess of that produced by application of the weight formula as defined in subparagraph (h), whichever is the greater. (d) For a single unit 5-axle heavy duty recovery vehicle, 80,000 pounds, or a gross weight not in excess of that produced by application of the weight formula as defined in subparagraph (h), whichever is the greater. Such vehicles shall have drive on 2 rear axles, and the tridem may contain not more than one retractable axle and, if not factory installed and load equalizing, must provide a system of load equalization by hydraulic, pneumatic, or mechanical means, and be equipped with brakes. (e) For a combination of truck-tractor and semi-trailer equipped with 3 axles, the gross weight shall not exceed that set forth in table I as follows: Table I. Distance Between Extreme Axles in Feet Maximum Gross Weight in Pounds 2554,500 2655,500 2756,000 2857,000 2957,500 3058,500 3159,000 3260,000 Further provided that the maximum tire and axle gross weights as provided in paragraph I shall apply and the maximum load in pounds carried on any group of 2 or more consecutive axles shall not exceed that produced by application of the weight formula as defined in subparagraph (h). (f) For a combination of truck-tractor and semi-trailer equipped with 4 axles, the gross weight shall not exceed that set forth in table II as follows: Table II. Distance Between Extreme Axles in Feet Maximum Gross Weight in Pounds 2860,500 2961,500 3062,000 3162,500 3263,500 3364,000 3464,500 3565,500 3666,000 3766,500 3867,500 3968,000 Further provided that the maximum tire and axle gross weights as provided in paragraph I shall apply, and the maximum load in pounds carried on any group of 2 or more consecutive axles shall not exceed that produced by application of the weight formula as defined in subparagraph (h). (g) For a combination of truck-tractor and single semi-trailer with 5 or more axles with gross weight not in excess of 73,280 pounds, the weight on any single axle shall not exceed 22,400 pounds and the weight on any tandem axle shall not exceed 36,000 pounds. (h) For a combination of truck-tractor and single semi-trailer equipped with 5 or more axles with a gross weight in excess of 73,280 pounds or a combination of truck-tractor and more than one trailing unit, the total gross weight shall not exceed 80,000 pounds including all law enforcement tolerances, and the overall gross weight on a group of 2 or more consecutive axles shall not exceed that produced by application of the following formula, known as the weight formula: W = 500 { LN —— N − 1 + 12N + 36 } (In which W equals overall gross weight on any group of 2 or more consecutive axles to the nearest 500 pounds; L equals the distance measured to the nearest foot between the extreme of any group of 2 or more consecutive axles; and N equals the number of axles in the group under consideration.) Except that 2 consecutive sets of tandem axles may carry a gross load of 34,000 pounds each, provided the overall distance between the first and last axles of such consecutive sets of tandem axles is 36 feet or more and provided that such gross weight shall not exceed 80,000 pounds, including all law enforcement tolerances. The formula W = 500 { LN —— N − 1 + 12N + 36 } when expressed in tabular form results in maximum allowable load in pounds carried on any group of 2 or more consecutive axles as follows in table III. Table III. Distance* 2 axles 3 axles 4 axles 5 axles 6 axles 7 axles 4 34,000 5 34,000 6 34,000 7 34,000 8 and less 34,000 34,000 more than 8 38,000 42,000 9 39,000 42,500 10 40,000 43,500 11 44,000 12 45,000 50,000 13 45,500 50,500 14 46,500 51,500 15 47,000 52,000 16 48,000 52,500 58,000 17 48,500 53,500 58,500 18 49,500 54,000 59,000 19 50,000 54,500 60,000 20 51,000 55,500 60,500 66,000 21 51,500 56,000 61,000 66,500 22 52,500 56,500 61,500 67,000 23 53,000 57,500 62,500 68,000 24 54,000 58,000 63,000 68,500 74,000 25 54,500 58,500 63,500 69,000 74,500 26 55,500 59,500 64,000 69,500 75,000 27 56,000 60,000 65,000 70,000 75,500 28 57,000 60,500 65,500 71,000 76,500 29 57,500 61,500 66,000 71,500 77,000 30 58,500 62,000 66,500 72,000 77,500 31 59,000 62,500 67,500 72,500 78,000 32 60,000 63,500 68,000 73,000 78,500 33 64,000 68,500 74,000 79,000 34 64,500 69,000 74,500 80,000 35 65,500 70,000 75,000 **36 66,000 70,500 75,500 **37 66,500 71,000 76,000 **38 67,500 71,500 77,000 39 68,000 72,500 77,500 40 68,500 73,000 78,000 41 69,500 73,500 78,500 42 70,000 74,000 79,000 43 70,500 75,000 80,000 44 71,500 75,500 45 72,000 76,000 46 72,500 76,500 47 73,500 77,500 48 74,000 78,000 49 74,500 78,500 50 75,500 79,000 51 76,000 80,000 52 76,500 53 77,500 54 78,000 55 78,500 56 79,500 57 80,000 * Distance in feet between the extremes of any group of 2 or more consecutive axles. **Distance in feet between the extremes of 4 axles. (2 sets of 2 axles) 68,000 gross weight exception. The permissible loads are computed to the nearest 500 pounds. (i) The following loaded vehicles shall not be driven over H15-44 bridges: (1) A combination vehicle equipped with 5 axles in the configuration of 3-axle truck-tractor and 2-axle semi-trailer with wheel base less than 38 feet or 2-axle truck-tractor with 1-axle semi-trailer and 2-axle full trailer with wheel base less than 45 feet. (2) A loaded single unit vehicle with full trailer equipped with axles with wheel base less than 45 feet. (3) Vehicles with 7, 8, or 9 axles. (j) Coupled vehicles consisting of a truck together with a trailer attached to the truck by a pintle hook or similar coupling device with adequate breakaway protection as provided in RSA 266:63 may be driven, provided the total combined gross weight of the vehicles does not exceed 80,000 pounds and provided that each unit of the coupled vehicles shall be limited to the maximum permissible axle weights and gross weights of the individual units, and further provided that the weight of 2 or more consecutive axles of the coupled vehicle shall not be in excess of that produced by application of the weight formula as defined in subparagraph (h) and shall be limited to a total combined gross weight not in excess of 80,000 pounds, a single axle limit of 20,000 pounds and a tandem axle limit of 34,000 pounds. III. Notwithstanding paragraphs I and II, for as long as exemptions exist in 23 U.S.C. section 127 that allow maximum gross weights of up to 99,000 pounds on interstate routes 89, 93, and 95 of the interstate and defense highway system, the provisions of RSA 266:18-a regarding weight on the non-interstate and general highway system shall also apply to vehicles or combination vehicles while being operated on any sections of interstate routes 89, 93, or 95 not posted by the commissioner of transportation for lower weights. Such vehicles shall not exceed the weight limits in paragraphs I and II unless they have been certified pursuant to RSA 266:18-d for the higher weights and paid the required fee the same as vehicles operating on the non-interstate highways as provided in RSA 266:18-d.